AGCO Automotive Vehicle Questions Page

 AGCO Automotive Vehicle Questions
Transmission, Clutch and Differential
QUESTIONS
  1. After changing the differential fluid in my four-wheel drive truck, there is a distinct popping noise in the rear, when turning. I have checked and the proper oil was used?
  2. After driving a while, if I accelerate my car does not speed up. Could this be the automatic transmission?
  3. After I drive for a while, my transmission sticks in 2nd gear and will not shift up or down. I was told this means I need a new transmission.
  4. After my engine overheated my mechanic suggested I have the automatic transmission serviced. Why would he suggest this?
  5. After replacing the clutch in my vehicle, there is a shudder when it engages.
  6. After replacing the clutch master cylinder in my vehicle, the pedal just goes to the floor?
  7. After replacing the rear differential oil, the rear end in my vehicle started to leak. I added the amount of oil specified, could I have over filled it?
  8. Can a driveshaft cause my vehicle to vibrate?
  9. Can a leaking rear axle pinion seal cause the transmission to leak?
  10. Can a rear wheel-drive drive shaft be repaired?
  11. Can an extended warranty company insists on putting a used transmission in my vehicle?
  12. Can an improper ground cause a differential to fail?
  13. Can damage be done to the bearings of a differential, by being one quart low?
  14. Can I flush water out of an automatic transmission?
  15. Can I mix different brand names of oil used in my rear differential?
  16. Can I replace the solenoids in my automatic transmission, without removing the transmission from the vehicle?
  17. Can I reuse the transmission pan gasket when I service my transmission?
  18. Can low automatic transmission fluid damage a transmission?
  19. Can using the wrong size tires damage the rear differential in my truck?
  20. Checking prices on a rebuilt automatic transmission, I have received a huge variation. What is a fair price?
  21. Could a bad radiator cause my automatic transmission to overheat?
  22. Do I have to service my automatic transmission?
  23. Does metal in an automatic transmission pan mean the transmission is destroyed?
  24. Every once in a while the clutch pedal on my Jeep sinks to the floor and my transmission will not shift.
  25. Ford does not list differential fluid replacement, for my F150, in their maintenance schedule. Why should I replace the fluid?
  26. How can water get into my automatic transmission and what is the consequence?
  27. How critical is a leak in my automatic transmission?
  28. How do I know when my transmission is slipping?
  29. How does a factory re-manufactured transmission compare with a transmission rebuilt in a local shop?
  30. How does an automatic transmission torque converter work?
  31. How does park work in an automatic transmission?
  32. How does water entering a differential cause damage?
  33. How much should it cost to rebuild an automatic transmission?
  34. How often should differential oil be replaced?
  35. I am thinking of having an auxiliary cooler added to my automatic transmission. Are there any drawbacks, other than the cost?
  36. I checked my automatic transmission fluid and it showed low. After buying replacement fluid, I checked it again and now it reads full. How can that be?
  37. I had a bad U-joint in my driveshaft. After replacing the U-joints there is now a vibration in the vehicle at highway speed.
  38. I had a cooler added to my automatic transmission and the fluid temperature did not decrease?
  39. I had engine work performed on my Nissan. When I picked it up, the transmission was not shifting and the check engine light was on. A friend noticed the throttle position sensor unplugged. Do you think the transmission is damaged?
  40. I have a transmission with over 150K miles. I was told if I service it now, it may fail?
  41. I have a whining noise when my engine is running. How can I tell if it is an engine accessory or the automatic transmission?
  42. I have an automatic-transmission temperature gauge in my new vehicle. What is the normal temperature supposed to be?
  43. I have been told that overfilling my automatic transmission can cause damage, how critical is this?
  44. I have some old Dexron transmission fluid and was wondering if it will work in my truck that calls for Dexron-VI?
  45. I installed a stereo in my car and soon after the transmission failed. The transmission shop said the stereo caused the problem, is this possible?
  46. I like to downshift my transmission when coming to a stop, to save wear on my brakes. Does this harm the transmission?
  47. I recently bought a new vehicle and wonder if changing the automatic transmission fluid right away is a good idea?
  48. I recently bought a new vehicle and wonder if changing the automatic transmission fluid right away is a good idea?
  49. I recently had my transmission replaced and the shop recommended a rear main seal, even though it was not leaking. Is this just a sales gimmick?
  50. I was told a transmission flush would clean the transmission filter. Is this true?
  51. I was told my manual transmission requires a special fluid. Is this likely?
  52. I was told overfilling my automatic transmission could blow out the seals, is this true?
  53. If I replace the pinion seal on my differential, should I also replace the pinion nut?
  54. Is it possible to install the wrong filter in an automatic transmission?
  55. Is there a product that can restore an automatic transmission?
  56. Is there a simple test to see if a clutch is slipping?
  57. Is there anything I can do to help prevent rear differential problems?
  58. It is very difficult to shift my manual transmission into gear with the engine running. Does this mean the transmission is going bad?
  59. My automatic transmission failed and the shop insist on also replacing the battery cables. They said bad cables caused the failure, is this possible?
  60. My automatic transmission makes a whining noise and the fluid smells like burnt pop corn. Is this bad news?
  61. My automatic transmission started to slip badly and make a whining noise. After turning it off, it drove okay for a while and then started again.
  62. My automatic transmission was over a quart low on fluid but there are no leaks. Where else could the fluid go?
  63. My Dodge Caravan is setting DTC P0740, does that mean I need a rebuilt transmission?
  64. My engine sounds like it is running faster when I accelerate, is my automatic transmission going out?
  65. My Ford vehicle has a slight shudder, about 45MPH, that last only about a second or two. It feels almost like running over a rough patch in the road, but is there even on smooth roads.
  66. My front-wheel drive car vibrates when I accelerate and stops when I release the accelerator. Any ideas?
  67. My older Ford vehicle calls for Mercon automatic transmission fluid. Will it hurt to use MerconV?
  68. My rear differential axle seals had to be replaced twice. What do you think is the cause?
  69. My rear differential failed and I was told it was because it had water in the oil. How could water get into a differential?
  70. My transmission slips or goes to neutral when I turn a fast corner
  71. My truck has a whine on acceleration, any ideas?
  72. My vehicle does not roll easily and feels like something is holding it back. If I let off the brakes, it barely moves. Both outer C.V. joints are clicking on turns, could this be the cause?
  73. My vehicle manufacturer says that the automatic transmission fluid doesn’t need changing. Change or leave it alone?
  74. On a hot day, when my vehicle has been idling for a while, the engine sounds like it is running very fast. The tachometer indicates normal, could my transmission be slipping?
  75. Recently I had to have my differential repaired. What things lead to differential failure?
  76. Servicing the transmission on my Ford, I found a small plastic part with an O-ring on it, lying in the pan. I have not been able to find any place for it to go.
  77. Since jacking up the height of my Jeep I keep breaking the driveshafts. What should I do?
  78. The automatic transmission fluid in my new car seem very dark, should I be concerned?
  79. The axle shafts in my rear differential wore out. What could have caused this?
  80. The clutch in my vehicle started slipping and had to be replaced at 40K miles. Is this normal?
  81. The clutch pilot bushing will not come out of the end of the crankshaft in my truck. I have tried a puller with no luck. Any ideas?
  82. The pinion seal of my vehicle keeps leaking and has been replaced twice?
  83. The rear differential of my truck is puking gear oil from the vent, any ideas?
  84. The rear pinion seal in my vehicle is leaking. I was told it is necessary to disassemble the rear end to replace the seal. Can the seal be replaced without that additional cost?
  85. The rear wheels on my General Motors truck seem to lock up from time to time?
  86. The shifter on my Chevy Silverado is hard to move.
  87. The transmission on my Ford Explorer does not have a dipstick. Can the fluid still be checked?
  88. There is a bearing type noise in the rear of my rear wheel drive vehicle. Accelerating and decelerating does not affect it. Could it still be a differential problem?
  89. There is a lot of slack in my rear differential, can this be adjusted?
  90. There is a whine in my vehicle that goes away when the clutch is fully depressed.
  91. There is a whine in my vehicle that starts when the clutch is depressed.
  92. There is a whining noise in my truck, when driving at speed. If I accelerate it gets worse and almost quits when I decelerate?
  93. What are the symptoms of a bad automatic transmission torque converter?
  94. What are the symptoms of a plugged transmission filter?
  95. What color is automatic transmission fluid?
  96. What could cause a pinion nut to loosen itself?
  97. What does it mean when a transmission goes into lock up?
  98. What does water in an automatic transmission look like?
  99. What is a limited slip differential?
  100. What is meant by a lower ratio rear end?
  101. What is the best way to remove a universal joint without damaging the driveshaft?
  102. What is the danger of driving with an automatic transmission leak?
  103. What is the difference in a transmission flush and a service?
  104. What is the harm of driving with a bad U-joint?
  105. What is the normal life of rear axle bearings?
  106. What makes a C. V. joint fail?
  107. What should I do if my automatic transmission fluid is dark?
  108. When driving my engine seems to be racing. I had the automatic transmission checked and there was no problem. Any ideas?
  109. When my transmission was serviced, a piece of a snap ring and some metal was found in the pan. It still works fine, should I be concerned?
  110. Where does the slop in my Ford rear end come from?
  111. Why do you think some manufacturers do not recommend automatic transmission service?
  112. Why is my shifter stuck in park?
  113. Why is transmission fluid red?
  114. Why would a new transmission pan gasket leak?
  115. Why would an automatic transmission move while in neutral?
  116. Why would my vehicle roll after being put in park?
  117. Why would RPM increase but the vehicle not move when in drive?
  118. Why would the flexplate, on my engine, suddenly break?
  119. Why would transmission temperature go up when towing?
  120. Will over tightening my transmission pan cause it to leak?
  121. Will servicing my automatic transmission keep it from failing?
ANSWERS
  1. After changing the differential fluid in my four-wheel drive truck, there is a distinct popping noise in the rear, when turning. I have checked and the proper oil was used?

    Very likely the vehicle has a limited-slip differential. These sometimes require a special additive, to be added to the oil, for the limited-slip clutches. turning the vehicle, the clutches must slip. Without limited slip additive, the clutches will often make a noise as you describe.
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  2. After driving a while, if I accelerate my car does not speed up. Could this be the automatic transmission?

    If the engine speed increases (RPM goes up) and the miles per hour do not, the transmission could be the cause. If the RPM does not increase when you accelerate, an engine running problem is far more likely. The two are quite often confused as a poorly running engine can make the transmission behave strangely. This is where a full service shop, with experts in drive-ability and transmissions can be invaluable.

    For more on diagnosing transmission problems, see our article Transmission Problems?.
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  3. After I drive for a while, my transmission sticks in 2nd gear and will not shift up or down. I was told this means I need a new transmission.

    There could be several causes for this problem, some serious and some not. Often an electrical problem, outside the transmission, can cause the transmission control module (TCM) to become confused. When this occurs, many vehicles will lock in second gear as a limp-home or limp mode. Sometimes turning the ignition off and re-starting the vehicle, will clear the problem, until it occurs again.

    Getting the vehicle to a trusted professional is very important. They can test inputs to the transmission, control pressure and determine if the problem is electrical or a transmission issue. Sometime something as simple a bad alternator or a loose ground wire can cause such an issue. Internal slippage in the transmission can also result in limp mode. Because of the huge variation in price, choosing a knowledgeable and trusted shop is imperative.
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  4. After my engine overheated my mechanic suggested I have the automatic transmission serviced. Why would he suggest this?

    Heat is one of the leading causes of transmission problems. The transmission fluid is normally cooled by the engine radiator and engine heat is transferred to the transmission. I agree, properly servicing the transmission after overheating the engine, is a very wise precaution against problems.

    For much more on proper transmission service, please see our article Transmissions and proper service.
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  5. After replacing the clutch in my vehicle, there is a shudder when it engages.

    Clutch shudder can have several causes. One of the most common is a clutch disk damaged in installation. If the weight of the transmission is not properly supported, the clutch disk can be bent. This will cause the disk to wobble and produces a shudder on engagement. A few other possible causes include a worn out or missing pilot bushing, a damaged clutch pressure plate, broken engine supports or a rough flywheel surface.
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  6. After replacing the clutch master cylinder in my vehicle, the pedal just goes to the floor?

    Likely there is still air trapped in the system. Since air is compressible, the fluid does not hydraulically transfer the pedal pressure to the slave cylinder. Bleeding clutches can be very difficult. We use several methods, depending on the application. Sometimes, reverse bleeding works. This is applying fluid, under pressure to the slave cylinder. This forces air upward and out of the master cylinder reservoir, using a special pump tool made for this purpose.

    In cases where the master cylinder mounts at an upward angle on the vehicle, it is sometimes necessary to remove and bleed it separately. The upward tilt can trap air at the end of the cylinder. It is also often helpful to tap gently on the cylinder and allow time for trapped air bubbles to rise to the reservoir.
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  7. After replacing the rear differential oil, the rear end in my vehicle started to leak. I added the amount of oil specified, could I have over filled it?

    Oil will leak until the level of the oil is below the level of the leaking seal. Chances are the differential was low due to the leaking seals. Servicing it brought the fluid to the proper level, above the level of the leaking seal.

    See our Detailed Topic Rear Axle Bearing Failure for more information.
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  8. Can a driveshaft cause my vehicle to vibrate?

    On front-wheel drive vehicles, the drive-shafts rotate at the speed of the wheels. If the shaft is bent or damaged it can cause the vehicle to vibrate. On rear-wheel drive vehicles, the drive shaft normally turns two and a half to four times the speed of the wheels. Because of the high speed and relatively large mass of rear-wheel drive shafts, vibration is vastly increased. Very small dents, missing balance weights and worn universal-joints all cause vibration. As a general rule, if the vibration is affected by acceleration and deceleration, check the drive shaft.

    For more information on universal-joints and driveshafts please see our Detailed Topic U-joints and Driveshafts.
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  9. Can a leaking rear axle pinion seal cause the transmission to leak?

    I can see nothing in a rear differential that would cause the transmission to leak. It is possible that a bad universal-joint or damaged drive shaft could cause both the pinion seal and the transmission output seal to leak.

    For more information on universal-joints and driveshafts please see our Detailed Topic U-joints and Driveshafts.
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  10. Can a rear wheel-drive drive shaft be repaired?

    Drive shafts are often repaired. They can be straightened or the tube replaced if bent too badly. They can also be balanced and the U-joints replaced among other things.

    For more information on universal-joints and driveshafts please see our Detailed Topic U-joints and Driveshafts.
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  11. Can an extended warranty company insists on putting a used transmission in my vehicle?

    An extended warranty is a contract between the company and the client. The terms of the contract, although they may be hard to read or understand, are the terms of the agreement. If the policy states used, rebuilt or aftermarket part will be used, that becomes the agreement the client has entered. This is unfortunate as in my experience, most folks do not consider this when buying the extended-warranty.

    For more information on extended warranty problems, please see our Detailed Topic, Extended Warranties, Avoid The Hook.


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  12. Can an improper ground cause a differential to fail?

    Improper grounds may cause transient current flow. Transient current flow can quickly destroy the differential, transmission, as well as several other components. Please see our Detailed topic Transient Current Flow for much more information.
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  13. Can damage be done to the bearings of a differential, by being one quart low?

    Bearing damage, from low lubricant level, would start with the axle bearings. Low oil level prevents them from being lubricated. When they fail, they can also contaminate the other bearings in the differential.

    See our Detailed Topic Rear Axle Bearing Failure for more information.
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  14. Can I flush water out of an automatic transmission?

    Water tends to dissolve the adhesives that bond clutches, in the transmission, together. The effect is almost immediate and devastating. Removing the water cannot undo the damage that has occurred. If the unit has not been driven, tear-down and replacement of the clutches, can prevent a great deal of further damage.
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  15. Can I mix different brand names of oil used in my rear differential?

    It is best not to mix any lubricant brands. Many brands may have similar initial viscosity and meet the same standards. This does not mean the additive packages are compatible. Modern lubricants are a combination of several additives that supply the needed characteristics. For example an anti-foam agent in one brand may not be compatible with a viscosity improver in another. This is particularly crucial in differentials, because of the extreme pressure that is borne by the lubricant.
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  16. Can I replace the solenoids in my automatic transmission, without removing the transmission from the vehicle?

    Solenoids can often be replaced without removing the transmission. It is also important to note that a leading cause of solenoid failure is metal and debris, generated by other problems within the transmission. Checking to learn the root cause of the failure may prevent further damage and expensive rework.
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  17. Can I reuse the transmission pan gasket when I service my transmission?

    Many transmission pan gaskets are designed to be reused and are of much higher quality than many of the replacement gaskets. These gaskets will normally be thick rubber type material and have metal reinforcement built in. Many times there will also be a label on the transmission pan. Non-reusable gaskets will normally be cork or thin fiber type material and have no reinforcement built in. If a reusable gasket must be replaced an exact replacement should be used.
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  18. Can low automatic transmission fluid damage a transmission?

    Yes, transmission fluid is the lubricant as well as the hydraulic fluid. Low fluid can result in a lack of lubrication and failure of the transmission.
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  19. Can using the wrong size tires damage the rear differential in my truck?

    Everything tends to be relative and a small amount of variation (one or two sizes) will normally not cause much damage. It will usually result in an incorrect speedometer reading and may effect transmission and ABS operation. Different size tires from side to side can cause problems. The shorter tire will have to rotate faster than the taller tire. This causes the differential spider gears to spin and can cause undue wear. The greater the difference, the greater the problem. With limited slip differentials the problem will be far worse.

    For more on how tire size affects speedometer error, please see our online calculator.
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  20. Checking prices on a rebuilt automatic transmission, I have received a huge variation. What is a fair price?

    There are a huge number of variances that may affect price. More confusing, there is no standard definition of what constitutes a rebuild nor the extent or quality of parts replaced. For instance what one shop calls a rebuild may simply be replacement of seals and clutches. Another shop may test every component and replace not only those parts that are bad, but all high failure components as well. This may include solenoids, sensors and so on. This may add several hundred dollars to the price, but prevent future problems and give far better results.

    Component quality is another huge variance. For instance a torque converter for a particular model may be available for $89.00 or $400.00 with a corresponding variance in quality. A better plan is to spend time researching the reputation of the shops you are considering. The price charged by a technically competent and honest shop will always be fair and reflect the highest value.

    For much more on proper transmission rebuilding, please see our article Transmissions: Repair, Rebuild or Replace.
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  21. Could a bad radiator cause my automatic transmission to overheat?

    The engine radiator also normally contains the transmission fluid cooler. A bad radiator can easily cause the transmission temperature to rise drastically and cause damage. Engine overheat is also transferred into the automatic transmission, which further overheats the transmission.
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  22. Do I have to service my automatic transmission?

    All vehicle maintenance, including automatic transmission service is optional, except as required by warranty agreements. The reason to service the automatic transmission is to lessen greatly the chances of an expensive transmission failure. Performing a proper transmission service cost a fraction of the cost of rebuilding the transmission or replacing the vehicle.

    For more information on the results of not performing maintenance, see our Detailed Topic Run Till Fail.
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  23. Does metal in an automatic transmission pan mean the transmission is destroyed?

    A very small amount of fine metal, may be acceptable, if there are no noticeable symptoms. This is where tiny flecks may be seen floating in the pan. When there is more metal, where the pan has a thin layer or pieces large enough to be felt with the fingers, normally mean transmission damage is occurring. It is also wise to remove the old transmission filter and break it open for a look inside. Many times, a significant amount of metal may be found inside the filter, even when the pan is relatively clean.

    An example of too much metal in an automatic transmission pan
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  24. Every once in a while the clutch pedal on my Jeep sinks to the floor and my transmission will not shift.

    This vehicle uses hydraulic cylinders to activate the clutch. Check to see if the fluid level in the clutch master cylinder is full. If the fluid is low, there is a leak either at the slave cylinder or sometimes out of the back of the master cylinder. If the reservoir is full, more likely the master cylinder is bypassing internally. This means when the pedal is pressed, the fluid leaks back to the master cylinder reservoir.

    Either condition will cause a drop in pressure in the system. Lack of pressure means the clutch does not release. With the clutch still engaged, the transmission will not shift.
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  25. Ford does not list differential fluid replacement, for my F150, in their maintenance schedule. Why should I replace the fluid?

    Vehicle makers are very interested in appearing to lower the cost of maintaining their vehicles. They are also responsible for the vehicle through the warranty period. Improper differential service or using the wrong or contaminated lubricant can cause warranty issues. It also allows inspection of the differential, which could point out early signs of problems and increase warranty cost.

    All lubricants degrade over time due to extreme pressure, heat, debris and use. Viscosity decreases and wear increases. Wear produces debris, which circulates with the oil and further increases damage. The differential oil is unfiltered so the effect is even more pronounced.

    Replacing differential oil removes much of the debris and replenishes the oil and additives needed to fight wear and keep seals pliable. Not replacing differential oil does NOT mean there will be a differential problem. Like all maintenance, properly replacing oil greatly decreases the odds of problems, by removing several of the primary causes.

    For more, see our Category on Differentials.
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  26. How can water get into my automatic transmission and what is the consequence?

    There are a few ways water may enter a transmission, and the result is almost always catastrophic failure. As with any petroleum lubricated component, the transmission is vented. This relieves pressure generated by gears churning through lubricant. It can also allow water to enter. Driving through high (6 inches or more) water may allow it to enter the transmission.

    A second common method is by radiator failure. Almost all automatic transmissions have a cooler, built into the radiator. The cooling element can rupture or crack. When the radiator pressure exceeds the transmission pressure, coolant may enter the transmission.
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  27. How critical is a leak in my automatic transmission?

    The severity of the leak largely determines how critical the problem is. Automatic transmission fluid is not only a hydraulic fluid. It also cools, cleans and perhaps most important, lubricates the transmission. When the fluid level drops, slippage may occur, which is extremely damaging. Lack of lubrication is also damaging. Most leaks only get worse in time. I feel it is wise to repair any significant automatic leak, immediately.
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  28. How do I know when my transmission is slipping?

    The easiest way to detect slip, is to watch the tachometer speed relative to vehicle speed. If the tachometer rises and vehicle speed does not increase, while the transmission is in gear, slipping is very likely.

    For more information on the gauges on the dash, please see or Detailed Topic, What Do The Gauges on The Dash Mean.


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  29. How does a factory re-manufactured transmission compare with a transmission rebuilt in a local shop?

    The answer really depends on the two businesses involved. A very good factory re-manufactured transmission is better than a mediocre shop rebuild. On the other hand, a high-quality shop can custom build the transmission, many times making it far better than the original. As a general rule, factory re-manufacturing is geared towards production and providing a product comparable to the original. Sometimes this is adequate. With transmissions that have known problems with durability, a quality shop-rebuild can provide a unit that is superior to the original.

    For much more on proper transmission rebuilding, see our article Transmissions: Repair, Rebuild or Replace.
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  30. How does an automatic transmission torque converter work?

    Inside the converter are sets of blades or fins. Some are attached to the drive shell and others to an output shaft. Fluid circulates through the converter and the fins churn through the fluid. At low speed, such as at an idle, the fins easily move through the fluid and no power is transmitted. As engine speed increases, the fluid transmits force from the drive fins to the driven fins and the vehicle moves.

    Most modern torque converters also have a set of clutches that lock at a certain speed, even further preventing slippage.

    torque converter effect is similar to one fan driving another
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  31. How does park work in an automatic transmission?

    Inside the transmission there is a park gear attached to the output shaft. A park pawl has a tooth that engages the park gear, locking the two together and preventing the output shaft from turning. Spring pressure holds the pawl out of the gear when not in use. When park is selected another spring loaded mechanism pushes the pawl into the park gear and prevents the transmission from turning.

    Park gear and parking pawl operation.
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  32. How does water entering a differential cause damage?

    Two primary sources of damage are corrosion to bearings and gears and destruction of the lubricating properties of the oil. Either can quickly destroy a differential. Corrosion, pits bearing and gear surfaces. The extreme loading of the hypoid gears cannot be supported by emulsified lubricant. The ring and pinion quickly scratch and gall their mating surfaces. When this occurs noise will begin and total failure is normally close behind.

    Ring gear worn from lack of lubrication.
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  33. How much should it cost to rebuild an automatic transmission?

    Unfortunately there is no specific answer as there are dozens of transmissions and each could have dozens of parts that fail. Complicating the matter much further is the definition of rebuild, which varies an incredible amount from one shop to another. For instance, one shop may replace the seals and clutches and call that a rebuild. Another may replace all parts that are worn as well as all parts that normally give problems, such as solenoids, sensors, valve body, etc. The quality of replacement parts will also vastly influence the price. A better bet may be to check into the reputations of several shops in the area and go with the shop known for honest, quality work. As with most things, you never get more than you pay for.

    For more information, please see our Detailed Topic Transmissions, repair, replace or rebuild.


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  34. How often should differential oil be replaced?

    Like any lubricant, differential fluid breaks down over time. As a general rule, it should be replaced around 50K to 100K miles or more often if towing or recommended by the manufacturer. Water entering through the vent or seals is another reason to replace immediately. This is a problem when driving in high water. Once water enters, it will emulsify the lubricant and cause rusting on bearing and gear surfaces.
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  35. I am thinking of having an auxiliary cooler added to my automatic transmission. Are there any drawbacks, other than the cost?

    Most auxiliary cooler installation problems relate to improper installation. Properly installed, the cooler should be mounted with its own bracket and suspended away from the radiator. Attaching a cooler to the radiator core with tie straps can cause damage and is not very effective.

    Tapping into the fluid flow causes other issues. Most factory systems employ metal cooler lines and crimped high pressure hoses. Cutting these lines presents an opportunity for a leak. Simply cutting the lines and attaching hoses with a clamp is very dangerous. Hoses attached in this manner can slide off causing the transmission to lose fluid. This is a fire hazard as well as quite damaging to the transmission.

    Improperly routed hoses can also kink and block the fluid flow. Transmission fluid is the lubricant for the transmission and blocking the flow can quickly result in major damage.
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  36. I checked my automatic transmission fluid and it showed low. After buying replacement fluid, I checked it again and now it reads full. How can that be?

    Transmission fluid will expand with temperature and should always be checked after the transmission is fully warmed up (up to 15 miles.) Other possibilities include not being on level ground, the engine not running or taking an improper reading.

    For more information, see our Detailed Topics article, Properly checking transmission fluid.
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  37. I had a bad U-joint in my driveshaft. After replacing the U-joints there is now a vibration in the vehicle at highway speed.

    Many driveshafts are balanced as an assembly when manufactured. This means if individual components are replaced the driveshaft may no longer be balanced.

    Balance on a driveshaft is extremely critical. The driveshaft is on the input side of the differential. If the differential ratio is three to one, the driveshaft turns three times faster than the wheels. With the relatively high mass and high speed of the shaft, imbalance will cause a distinct vibration.

    Driveshafts are also very fragile, normally constructed of a light gauge metal, often aluminum. Even the smallest dent or bent can very easily disturb balance. Driveshaft repair is a specialty and many larger cities have driveshaft repair shops. A qualified driveshaft shop can normally repair and if needed balance the shaft for you.
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  38. I had a cooler added to my automatic transmission and the fluid temperature did not decrease?

    Normal operating temperature should be around 175 degrees Fahrenheit. An additional cooler will not normally decrease this but should keep it from being exceeded as easily. They add cooling capacity to help with heavy use such as towing. Coolers are also not meant to cure problems with overheating. If the transmission was already running much above 175 degrees before installation and when not towing, there may be a problem in the transmission.
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  39. I had engine work performed on my Nissan. When I picked it up, the transmission was not shifting and the check engine light was on. A friend noticed the throttle position sensor unplugged. Do you think the transmission is damaged?

    I would not expect any damage, if the sensor was unplugged only for a short period of time. Lack of throttle signal will normally cause elevated pressure in the transmission. Over time this can cause excess wear and even break components. If the transmission has not been serviced recently, that may not be a bad precaution. This would give the opportunity to inspect the inside of the unit.

    For future reference, I would be concerned why the shop allowed the vehicle to leave with a check engine light and shifting improperly. This seems to indicate that they may not test drive the vehicles, which can be very problematic. A word with the shop manager may be in order. For help with addressing problems with a shop, please read our Detailed Topic, When Things Go Wrong.
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  40. I have a transmission with over 150K miles. I was told if I service it now, it may fail?

    A proper service can never damage a transmission, regardless of the mileage. The transmission could fail at this mileage, due to lack of service or wear, even if not serviced. Some shops are reluctant to service such a unit for this reason. As long as you understand the unit might fail regardless, a proper service could well extend the life of the transmission.
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  41. I have a whining noise when my engine is running. How can I tell if it is an engine accessory or the automatic transmission?

    A few quick test can help. First see if the noise is affected by shifting from park and into each gear. If the noise changes, or quits the transmission would be more suspect. A stethoscope can also be handy in isolating the area causing the noise.

    If the noise is not affected by shifting gears, temporarily removing the serpentine or drive belts from the engine and starting it can also point you toward an engine problem. If the noise goes away with the belts removed, it is likely a belt driven accessory. Of course the engine can only be run a few seconds without the belt(s).

    Finally, you can temporarily separate the torque converter from the flex plate and run the engine. Any whine that persist would have to be engine related.

    For more on noises related to transmission problems, see our article Transmission Problems?.
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  42. I have an automatic-transmission temperature gauge in my new vehicle. What is the normal temperature supposed to be?

    Transmission temperature can vary, depending on where the flow of fluid is measured. A temperature around 175 degrees Fahrenheit is usually considered normal. Heavy operation, such as towing will increase the temperature. As temperature rises, fluid life decreases. Every 20 degree, above 175 degrees Fahrenheit, can cut fluid life in half. Continued elevated temperature in normal driving can also be a sign of internal transmission problems. Continued elevated temperature often points to internal slippage and eminent transmission failure.

    For much more on proper transmission service, please see our article Transmissions and proper service.
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  43. I have been told that overfilling my automatic transmission can cause damage, how critical is this?

    Too much fluid is not a good idea as it can come out, through the dipstick and possibly vent tube. Since automatic transmission fluid is flammable it can present a fire hazard. Too much fluid will NOT damage the transmission otherwise. Overfilling an automatic transmission can make a mess and possibly start a fire, but not damage the transmission.

    For more information on properly checking automatic transmission fluid level see our Detailed Topics article, Properly checking transmission fluid.
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  44. I have some old Dexron transmission fluid and was wondering if it will work in my truck that calls for Dexron-VI?

    Dexron is a brand name used by General Motors for their transmission fluids. Dexron, Dexron-II and Dexron-III are conventional fluids. Dexron-VI is a synthetic based fluid. Dexron-VI could be used in place of Dexron, but not the other way around. Dexron does not meet the specifications of Dexron-VI and should not be substituted for it.
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  45. I installed a stereo in my car and soon after the transmission failed. The transmission shop said the stereo caused the problem, is this possible?

    If a ground was left off, disturbed or if excessive current flow was generated it is quite possible. Attaching the ground of a high current device to the engine can cause more draw than the battery ground can handle. The additional current will find a path to ground. This is often through the transmission.

    Please see our Detailed Topic Transient Current Flow for much more information.
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  46. I like to downshift my transmission when coming to a stop, to save wear on my brakes. Does this harm the transmission?

    Continuous downshifting can cause wear to the coast clutches, valve body and shifter linkage of the transmission. I would not advise using the transmission in this manner. To save wear to the brakes, anticipate stops and coast as long as possible. Hard application wears the brakes much faster.
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  47. I recently bought a new vehicle and wonder if changing the automatic transmission fluid right away is a good idea?

    Virtually all modern automatic transmissions use synthetic fluid and with advances in assembly methods, changing the fluid and filter right away is unnecessary. To be safe, I like to replace the fluid and if possible the filter at around 50,000 miles though many claim they can go as much as 100,000 miles before replacement. Especially on units with non-replaceable filters I think the 50,000 mile interval is a far less expensive strategy.
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  48. I recently bought a new vehicle and wonder if changing the automatic transmission fluid right away is a good idea?

    Virtually all modern automatic transmissions use synthetic fluid and with advances in assembly methods, changing the fluid and filter right away is unnecessary. To be safe, I like to replace the fluid and if possible the filter at around 50,000 miles though many claim they can go as much as 100,000 miles before replacement. Especially on units with non-replaceable filters I think the 50,000 mile interval is a far less expensive strategy.
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  49. I recently had my transmission replaced and the shop recommended a rear main seal, even though it was not leaking. Is this just a sales gimmick?

    The rear main seal is located between the engine and transmission. One or the other would normally need to be removed in order to replace the seal. Because of the amount of time required, this is normally an expensive repair. Replacing the seal, when the transmission is already out is very quick and inexpensive. If the vehicle has over 100,000 miles I think this would be a wise precaution.
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  50. I was told a transmission flush would clean the transmission filter. Is this true?

    Transmission filters are constructed much like a sock. The inlet is the opening or neck of the sock, into which fluid enters. The fluid then flows out through the pores of the filter into the filter case and then into the transmission. Any debris is trapped inside the filter and cannot be removed without disassembling the filter. A transmission flush will not clean a dirty filter. Rather, I feel the filter should be replaced as part of a proper transmission service.

    This is a transmission filter, that is cut open. The transmission had been flushed a few days before. Notice the amount of metal and debris still in the filter.
    Inside view of an automatic transmission filter and pan.

    For much more on proper transmission service, see our article Transmissions and proper service.
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  51. I was told my manual transmission requires a special fluid. Is this likely?

    Many vehicles do require special fluids in the transmission. Some also use 75W90 gear oil, 10W30 engine oil, automatic transmission fluid and several other fluids. It is always best to consult the manual that comes with the vehicle or some other reliable service information. A great deal of damage can occur from using the wrong fluid.
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  52. I was told overfilling my automatic transmission could blow out the seals, is this true?

    Overfilling a transmission may cause fluid to run out of the fill tube or vent, it cannot cause seals to blow out. Transmission fluid is flammable so overfilling is not a good idea however.

    For more information, see our Detailed Topics article, Properly checking transmission fluid.
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  53. If I replace the pinion seal on my differential, should I also replace the pinion nut?

    Pinion nuts are extremely high load components and failure can be catastrophic. Given their low cost, any time they are removed we recommend replacing the pinion nut.

    For much more on pinion set up, see our article Differential leaks.
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  54. Is it possible to install the wrong filter in an automatic transmission?

    It is not only possible, on some models it happens fairly frequently. GM rear wheel drive vehicles with the 4L60E transmission have three filters, depending on pan depth. We quite frequently see transmissions that have been serviced and the improper filter installed. This can cause problems ranging from delayed engagement, going to neutral in turns to damaging the transmission.
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  55. Is there a product that can restore an automatic transmission?

    Automatic transmissions are an accumulation of gears, solenoids, clutches and hydraulic circuits. Failure is often the result of broken parts, worn seals and the damage caused by the debris generated. No product added to a transmission will correct any of these problems.

    Immediate repair of a damaged part is the best bet as it can limit the collateral damage considerably. For instance a slight slip, from a worn band may be repaired by service and adjustment. Allowing it to slip, or adding an additive, can allow the band eat into the drum. This will create debris and possible total failure.

    For more information, see our Detailed Topics article, Properly checking transmission fluid.
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  56. Is there a simple test to see if a clutch is slipping?

    There is a simple test that is not definitive but will give a good indication of failure. This should be used with caution as you can damage a good clutch by overdoing it. Slowly pull the front wheels of the vehicle up to a high curb, so that they are blocked from rolling. Next apply the parking brake so the vehicle will not roll. Put the vehicle in third gear and bring the engine up to about 1,000 RPM. Slowly release the clutch and the engine should die immediately. If the engine runs at all, with the clutch out, the clutch is slipping. Slipping can cause a lot of damage very quickly, so this should only be done for a split second, no longer.
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  57. Is there anything I can do to help prevent rear differential problems?

    Driving habits can go a long way to extending the life of a differential. Shifting from drive to reverse or vice versa, while rolling can cause damage. Trying to rock a vehicle when stuck is another major problem. Calling a two truck is far less expensive than destroying a differential. Driving through any water that reaches the center of the wheels can also do damage.

    Replacing the differential fluid and keeping it full will extend the life of the unit. When towing or using the vehicle off road 30,000 miles or sooner if recommended by the manufacturer. Under normal use 50,000 to 100,000 miles is more common. Also inspecting the vent hose to make sure it is intact and attached, will help keep water out of the differential.

    For more, see our Category on Differentials.
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  58. It is very difficult to shift my manual transmission into gear with the engine running. Does this mean the transmission is going bad?

    If the transmission shifts normally without the engine running, the problem is more likely failure of the clutch to fully release. In order to shift gears the input shaft must be turning at the same speed as the gear selected. If the clutch does not release this is difficult and make shifting hard.

    A worn, damaged or rusted clutch can not release when depressed. There can also be a failure in the mechanism that releases the clutch. This is particularly common with hydraulic clutch release mechanism. The master and/or slave cylinders can leak and fail to disengage the clutch when the pedal is depressed. This usually causes a very soft pedal, with little resistance to be pushed.

    Another possibility is the input shaft binding in the pilot bushing, in the end of the crankshaft. This causes the input shaft to continue turning, even though the clutch is released.
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  59. My automatic transmission failed and the shop insist on also replacing the battery cables. They said bad cables caused the failure, is this possible?

    Transient grounds from bad battery cables can quite easily destroy a transmission. If the engine ground cable is not capable of returning the current used by the starter to the battery, it will find another path. This is sometimes through the transmission, out through the axles and back through the body ground. New or properly repaired cables are very good insurance if there is evidence of such a problem.

    For even more information on batteries and cables, see our Detailed Topics article, Replacing battery terminals.
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  60. My automatic transmission makes a whining noise and the fluid smells like burnt pop corn. Is this bad news?

    Actual burnt fluid almost always indicates a major problem. Whining noises can come from a plugged filter, caused by the burned material. Having the vehicle towed to a trusted professional may prevent further damage.

    See our Detailed Topic Dark Automatic Transmission Fluid for more information.
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  61. My automatic transmission started to slip badly and make a whining noise. After turning it off, it drove okay for a while and then started again.

    Slippage in a automatic transmission is a quick path to failure. Slipping clutches produce debris, which often clogs the filter. A clogged filter often produces a whine as it restricts the flow of fluid. When the engine is turned off the pump stops, fluid tends to flow back through the filter and temporarily clears part of the restriction. When running, the flow of fluid and debris will again cause the filter to plug.

    Another indication of serious problems would be fluid that is very dark, contains metal particles and/or has a burned smell. Continued driving is very unwise and will normally result in a much more expensive repair.
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  62. My automatic transmission was over a quart low on fluid but there are no leaks. Where else could the fluid go?

    First check the radiator to see if the coolant is oily. A leaking transmission cooler can allow leakage into the radiator. Also if the radiator has been replaced, transmission fluid is often lost. If the shop did not check the transmission, it may have not been refilled. Lastly, if a transmission service has been performed, the proper amount of fluid might not have been replaced.

    For much more on proper transmission service, see our article Transmissions and proper service.
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  63. My Dodge Caravan is setting DTC P0740, does that mean I need a rebuilt transmission?

    P0740 means the engine computer has detected slippage between the input and output of the transmission, when torque converter lock-up is being commanded. The first step is to see if the transmission is receiving the command to go to lock-up. If command is present, the next step is to perform a pressure test and see if internal pressure is proper. If there is no command, the problem can be electrical and outside of the transmission. If the pressure is not rising, the problem could be a solenoid not engaging. If pressure and command are present, the problem is more likely internal to the transmission.
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  64. My engine sounds like it is running faster when I accelerate, is my automatic transmission going out?

    If the RPM indicated on the tachometer rises significantly and the vehicle does not speed up, transmission slippage is a likely cause. There are also a great many things, from an engine running problem to a stuck fan clutch that can cause similar symptoms. Check the transmission fluid color. If it is black or smells burnt, have the transmission checked. If not the problem could easily be something less serious.

    Also see our Detailed Topic Transmission Problems? for more information on things mistaken for transmission problems.
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  65. My Ford vehicle has a slight shudder, about 45MPH, that last only about a second or two. It feels almost like running over a rough patch in the road, but is there even on smooth roads.

    One common cause is torque converter lockup shudder. At around 45MPH the torque converter clutch locks to prevent further slippage and enhance fuel mileage. If the clutch lockup is not smooth, there will be a noticeable shudder. A quick test is to touch the brake pedal and see if it immediately stops. Applying brakes signals the system to come out of lockup.

    Left untreated, the converter can be damaged and require replacement. At AGCO, we have had very good luck servicing the transmission, with Ford synthetic fluid. We also re-torque the valve body bolts and replace the filter. In many instances this corrects the problem, if it has not gone too far.
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  66. My front-wheel drive car vibrates when I accelerate and stops when I release the accelerator. Any ideas?

    Two common causes of vibration on acceleration are broken engine/transmission supports and worn inner C.V. joints. Engine mounts can often be detected by watching the engine, while someone holds the brakes tightly and with the car in gear. Very carefully apply slight throttle and see if the engine move significantly. Obviously great caution must be used, and damage can occur if not careful. It also takes a bit of experience to determine how much movement is normal.

    Inner C.V. joints are even more difficult to test. Often they must be disassembled and professionally inspected to find the damage.
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  67. My older Ford vehicle calls for Mercon automatic transmission fluid. Will it hurt to use MerconV?

    Mercon is a brand name used by Ford Motor Company to describe their automatic transmission fluid. The original Mercon was roughly equivalent and interchangeable with Dexron. MerconV is a synthetic fluid, formulated for the requirements of later model transmissions. MerconV exceeds the specifications of Mercon and can be used to replace it.
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  68. My rear differential axle seals had to be replaced twice. What do you think is the cause?

    Improper installation is possible. Seals must be handled quite gently and installed properly. The sealing surface must also be lubricated on installation. Failure to lubricate the seal will normally cause failure in short order. Other causes of recurring problems are a damaged axle, on which the seal rides and a plugged axle housing vent. Differentials are lubricated with petroleum which builds pressure as the gears rotate. This pressure is relieved by the housing vent. Plugging the vent will result in oil being forced past seals, by the pressure buildup.

    See our Detailed Topic Rear Axle Bearing Failure for more information on axle seals.
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  69. My rear differential failed and I was told it was because it had water in the oil. How could water get into a differential?

    Rear differentials are sealed, but are not water tight. The seals are mainly designed to keep oil in, not water out. Driving through high water (above the centerline of the wheels) can cause water to leak past the seals. If the rear vent hose is broken missing or damaged the problem will be far worse. Driving in the rain can cause water to enter through a damaged vent hose.

    For more on drain hose problems, see our Category on Differentials.
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  70. My transmission slips or goes to neutral when I turn a fast corner

    This is often caused by low fluid level, the wrong or improperly installed filter. Fluid tends to slosh when cornering. If the fluid fails to cover the filter, pressure will be temporarily lost and slippage will occur. Low fluid level is a common cause. Also note that low fluid level usually means a leak.

    Many transmission types come with different depth pans, when used in different models. For instance the 4L60E Chevrolet truck transmission could have at least three filter depth. Since all will physically fit, a filter that is too short could inadvertently be installed. This would give much the save effect as low fluid, even though the level indicates correct.

    For more information, see our Detailed Topics article, Properly checking transmission fluid.
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  71. My truck has a whine on acceleration, any ideas?

    First test should be to see if the whine also occurs when sitting still and accelerating in neutral. If so, the whine could be an engine accessory or transmission related. If temporarily removing the engine accessory belt(s) eliminates the noise, an engine accessory is the likely cause.

    If the noise cannot be duplicated while sitting still, it is more likely a drive-line related. This is particularly so if the noise tends to change drastically on acceleration and deceleration. Bad pinion bearings, misaligned ring and pinion gears and worn gear teeth all tend to make a characteristic whine on acceleration and sometimes on deceleration.
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  72. My vehicle does not roll easily and feels like something is holding it back. If I let off the brakes, it barely moves. Both outer C.V. joints are clicking on turns, could this be the cause?

    Clicking C.V. joints do indicate a problem, but not likely the symptoms you describe. More likely would be brake drag from one or more wheels.

    Please also see Basic Hydraulic Brake Diagnosis and Repair for far more detail.


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  73. My vehicle manufacturer says that the automatic transmission fluid doesn’t need changing. Change or leave it alone?

    Manufacturers may feel the odds of problems from improper service are greater than the odds of problems from no service at all. The wrong fluid, not enough fluid, the wrong filter or one not properly installed may quickly ruin a transmission. Over filling a transmission can present a fire hazard. I think their recommendation is based on this and a supposed vehicle life of no more than 100K miles.

    With proper transmission service, vehicles stand much less chance of lubrication related problems. Lack of service may cause failure from restricted filters, debris and depleted fluid. A proper service can never hurt the vehicle and may extend transmission life, especially if the vehicle is driven beyond 100K miles.

    For much more on proper transmission service, see our article Transmissions and proper service.
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  74. On a hot day, when my vehicle has been idling for a while, the engine sounds like it is running very fast. The tachometer indicates normal, could my transmission be slipping?

    If the tachometer shows normal RPM for the speed driven, the transmission is likely not slipping. If the noise only occurs on hot days and after sitting at an idle, I would suspect the cooling fan(s). Electric cooling fans are commanded to high as temperature increases. Mechanical fans normally have a clutch that increases fan speed as temperature rises. Running at high speed the fans create a noise, much like the engine running faster. This is normal operation, as long as the noise goes away after driving at speed and when the engine cools down.
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  75. Recently I had to have my differential repaired. What things lead to differential failure?

    Like any component, the differential is subject to wear and some fail before others. Breakdown of the special lubricant or use of the wrong type lubricant are leading causes. Water entering through the vent or seals is another. This is a problem when driving in high water. Once water enters, it will emulsify the lubricant and cause rusting on bearing and gear surfaces.

    Other damage can be caused by seized U-joints causing vibration. Catastrophic failure, like gear breakage is often caused by abuse. Shifting from reverse to drive with the vehicle in motion is one such cause. Another is towing or hauling more weight than the vehicle is designed to carry.
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  76. Servicing the transmission on my Ford, I found a small plastic part with an O-ring on it, lying in the pan. I have not been able to find any place for it to go.

    Many people have been confused when finding this part in their transmission. It is a plug, used in shipping the transmission. When the dipstick is pushed in, it falls into the pan. Ford elected to leave it there, they cause no harm other than to confuse folks who find them.
    Ford transmission dipstick shipping plug
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  77. Since jacking up the height of my Jeep I keep breaking the driveshafts. What should I do?

    Raising the vehicle changes the angle at which the U-joints must operate. U-joints are not designed for extreme angles, are overloaded and quickly fail. Returning the vehicle to stock height would be the least expensive option. If that is out, aftermarket companies produce driveshafts with C.V. joints that can handle a much greater angle, with less problems.

    For a lot more information on modifying vehicle suspensions, see our Detailed topic, Lowering and Raising Vehicle Suspensions.
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  78. The automatic transmission fluid in my new car seem very dark, should I be concerned?

    Fluid color is an indication of a possible problem, but not necessarily. Many modern automatic transmission fluids are darker, even when new, than fluids of the past. If the fluid does not have a burned smell and there are no other symptoms, chances are it is not a problem. Best would be to have it inspected by a trusted professional.

    See our Detailed Topic Dark Automatic Transmission Fluid for more information.
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  79. The axle shafts in my rear differential wore out. What could have caused this?

    Rear axle bearings often roll directly on the axle shaft. If they are not properly lubricated, they can quickly destroy the axles. Lubrication of the rear axle bearings is a function of oil level and condition in the rear differential. Any leakage can cause the fluid level to drop. When the level drops, the axles may no longer receive lubrication. Rear differential fluid level should be checked whenever there is a leak and the oil should be replaced at recommended intervals.

    See our Detailed Topic Rear Axle Bearing Failure for more information.
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  80. The clutch in my vehicle started slipping and had to be replaced at 40K miles. Is this normal?

    Clutch life is almost entirely under the control of the driver. Many clutches last the life of the vehicle or they can be worn out in 10K or less miles from mis-use. Riding the clutch or keeping a foot on the clutch pedal when driving can cause very rapid wear. Allowing the clutch to partially engage to hold the vehicle stationary on an incline is another way to wear it very quickly.

    For best life, the clutch pedal should be fully engaged (foot off the pedal) or fully dis-engaged (pedal to the floor.) Partially engaging and dis-engaging causes slippage and wear. Jack-rabbit starts and popping the clutch also causes wear.
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  81. The clutch pilot bushing will not come out of the end of the crankshaft in my truck. I have tried a puller with no luck. Any ideas?

    An old trick that works well, is to pack the area behind and the hole of the bushing with a heavy grease. Next find a metal rod that will just slip into the pilot bearing hole. Use a hammer to drive the rod into the bushing. Hydraulic force will cause the bushing to be pushed out as the rod is driven in.

    Removing pilot bushing with grease and a rod
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  82. The pinion seal of my vehicle keeps leaking and has been replaced twice?

    Assuming the seal was properly installed, there are things that can result in repeated failure. A plugged axle vent can allow pressure to build and ruin a good seal. A bad pinion bearing can allow slack that the seal cannot control. A groove in the seal surface of the pinion flange can also result in repeated leaks. Finally a rear U-joint that is tight can cause a vibration that will quickly destroy the pinion seal.
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  83. The rear differential of my truck is puking gear oil from the vent, any ideas?

    The most common cause is aeration of the oil. This is normally caused by contamination and results in millions of tiny bubbles causing the oil to greatly expand. I have also seen cases of a partially restricted vent causing this problem. The pressure is increased to a point where oil slung by the ring gear is blown out, rather than falling back to the lower end of the housing.
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  84. The rear pinion seal in my vehicle is leaking. I was told it is necessary to disassemble the rear end to replace the seal. Can the seal be replaced without that additional cost?

    The answer depends on the design of the rear differential. Many differentials employs a crush sleeve to establish bearing pre-load and gear alignment. If this is the case, replacement of the crush sleeve is necessary and would require disassembly of the differential.

    For much more on proper seal replacement, see our article Differential leaks.
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  85. The rear wheels on my General Motors truck seem to lock up from time to time?

    Around 1973, General Motors adopted the Eaton gov-lock traction assist differential. This was in an effort to eliminate clutch chatter associated with the clutch and spring type locking differentials. Instead, centrifugal force causes a counter-weight to move and lock the rear differential under wheel slip conditions. This works okay for the average driver and with intermittent use. Normally releasing the throttle for a few seconds will allow the unit to come out of lock-up.

    In more severe cases the spring controlling the counter weight can break causing undesired locking. Repair is relatively minor as long as it is addressed early. Continued or heavy duty use can damage the unit severely, escalating cost drastically.
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  86. The shifter on my Chevy Silverado is hard to move.

    The shifter cable on these vehicles can fail over time and the cable will no longer move freely. When this happens movement of the shift lever will become difficult. Eventually the cable and break and the transmission will no longer shift. The added strain can also damage components in the steering column. Replacement of the cable is the best repair.
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  87. The transmission on my Ford Explorer does not have a dipstick. Can the fluid still be checked?

    It can, but is a bit more difficult. The vehicle must be at operating temperature, running in park, level and raised in the air for access. In the bottom of the transmission pan, there is a large hex shaped head, with a small hex shaped plug in the center. Remove the small hex plug and if fluid drips out the transmission is full. If not it is low and a special tool is needed to fill.

    Be careful not to remove the large plug as this is the drain plug and it will empty the pan.
    Pan design for Ford 5R55W, N and S transmissions

    For more information, see our Detailed Topics article, Properly checking transmission fluid.
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  88. There is a bearing type noise in the rear of my rear wheel drive vehicle. Accelerating and decelerating does not affect it. Could it still be a differential problem?

    Yes, it could. Bad pinion bearings and gear problems will often change when you accelerate or decelerate. Carrier bearings and/or axle bearings normally do not. Other commonly mis-diagnosed sources of noise, in the rear of the vehicle, include chopped tires and driveshaft carrier bearings.

    A tire worn in a chopped pattern is often the result of rear end misalignment. They make a noise very similar to a bad bearing. I always recommend temporarily rotating the tires as a diagnostic procedure. If the noise changes pitch or intensity, the tire may well be the cause.
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  89. There is a lot of slack in my rear differential, can this be adjusted?

    Slack that develops in a rear differential is a sign of wear or part failure. Adjustment between the gears is controlled by shims or threaded adjustments which do not move once put in place. More likely is wear to bearings and/or the internal gears.

    Proper repair involves disassembly, inspection and replacement of worn parts. Bearing, seals and smaller internal gears can often be replaced without having to replace the more expensive ring and pinion gears. Continued driving will almost always result in more extensive damage and a higher cost of repair.
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  90. There is a whine in my vehicle that goes away when the clutch is fully depressed.

    When the clutch is depressed the transmission is unloaded, or detached from engine power. Likely the noise is coming from bearings inside the transmission, such as the input bearing and main-shaft bearings.
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  91. There is a whine in my vehicle that starts when the clutch is depressed.

    When the clutch is depressed the throw-out bearing starts to turn. This is one possible source of noise. Another would be the pilot bushing, where the input shaft of the transmission enters the crankshaft. This noise may also get louder with the vehicle sitting still and the transmission in gear. Again sitting still, it may be less noisy with the transmission in neutral. The throw-out bearing should not be affected by transmission position selection.
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  92. There is a whining noise in my truck, when driving at speed. If I accelerate it gets worse and almost quits when I decelerate?

    This is a classic symptom of differential noise on a rear wheel drive vehicle. The cause is often bad pinion bearing and/or the ring and pinion gears out of alignment. The problem is very serious and will get much more expensive if not addressed quickly.

    Repair involves disassembly and inspection of the gears and bearings. If the gears are not damaged, you may be able to replace bearings and re-set the gear alignment. This is very specialized work and best left to a professional.
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  93. What are the symptoms of a bad automatic transmission torque converter?

    As with most components the symptoms will depend on the nature of the failure. Noise coming from the front of the transmission that increases with engine speed is common. Engine RPM may also increase, relative to MPH when driving. Another symptom may be elevated transmission temperature and on newer vehicles a check engine light.

    A slight to moderate shudder in the vehicle, when going into lock up, may be converter related, but does not necessarily mean failure. Many people describe the feeling as similar to running over a rough patch in the road. Touching the brake pedal while it occurs will normally cause it to stop. Torque converter shudder can often be repaired by a proper transmission service.
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  94. What are the symptoms of a plugged transmission filter?

    A plugged transmission filter is actually a symptom in and of itself. Transmissions do not generate large amounts of debris needed to plug a filter unless there is a failure. Normally the clutch and/or band material are badly worn producing the debris. Once the filter is restricted, pressure that applies the clutches and bands is decreased. This increases wear even further and normally shows up as slippage. Slippage is indicated when accelerating, by an increase in engine speed without an increase in vehicle speed. Other symptoms may include the transmission failing to engage after a short drive and whining/whistling noise from the transmission.
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  95. What color is automatic transmission fluid?

    Automatic transmission fluid is dyed red for identification. The shade will vary from a light red to a deep red, depending on type. It also tends to darken with age and can turn very dark or black when there is a problem.

    See our Detailed Topic Dark Automatic Transmission Fluid for more information.
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  96. What could cause a pinion nut to loosen itself?

    The tension on the pinion nut is maintained by the components behind it. This usually includes the two pinion bearings, sometimes a spacer and a crush sleeve. If a bearing[s] fails, additional space is created and tension is reduced. Simply tightening the nut will normally only speed the deterioration. Instead the differential should be professionally checked to determine and eliminate the root cause. Quick action can prevent an even bigger repair.

    For much more on pinion set up, see our article Differential leaks.
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  97. What does it mean when a transmission goes into lock up?

    Lock up is a term meaning the internal clutch in the torque converter has applied. Once applied the output speed of the torque converter matches the input and there is greatly reduced slippage. The driver will normally notice a slight drop in engine RPM with no reduction in vehicle speed.
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  98. What does water in an automatic transmission look like?

    Water turns milky colored when mixed with automatic transmission fluid. Normally by the time this can be seen, there is a substantial amount of water is in the fluid. Water tends to dissolve the adhesives that bond clutches together. Even with much smaller amounts of water, severe damage quickly occurs.

    Water in automatic transmission fluid.
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  99. What is a limited slip differential?

    When a vehicle goes around a curve, the outside wheel travels a larger radius than the inside wheel. This means the outside wheel must turn faster and the differential allows this. Limited slip is a system that uses clutches or a locking mechanism to conduct power to both drive wheels. The mechanism is designed to allow wheels to turn at different speeds in turns and have them both pull when driving straight. This adds the advantage of both wheels pulling when one wheel loses traction.
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  100. What is meant by a lower ratio rear end?

    Ratio relates to the gears in the differential. A gear ratio is expresses as a number, which basically means the number of turns required on the input to get one turn on the output. For instance 3.43 means the driveshaft turns 3.43 times for every time the rear wheels turn once. The higher the number, the lower the ratio of the gear. This means the engine will turn faster, in relation to the speed of the vehicle. A 3.73 ratio gear is said to be a lower ratio than a 3.43 gear.

    Perhaps over simplified, lower ratios produce more torque and pulling power. Higher gear ratios slow the engine, in relation to vehicle speed and can give better fuel economy and perhaps a higher top speed.
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  101. What is the best way to remove a universal joint without damaging the driveshaft?

    There are various tools designed to remove u-joints without damage. Most will concentrate force between the cap and yoke, rather than pressing the yokes together. Any distortion of the yokes or bending of the shaft can ruin the driveshaft and cause considerable vibration.

    For more information on universal-joints and driveshafts please see our Detailed Topic U-joints and Driveshafts.
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  102. What is the danger of driving with an automatic transmission leak?

    The extent of danger depends on the leak. For instance, a cooler line that is loose or a bad cooler line hose can suddenly blow all of the fluid out of the transmission. This combines a huge fire hazard with the likelihood of almost immediate transmission failure. Any leak is likely to get worse in time. Losing transmission fluid deprives the automatic transmission of lubricant and hydraulic fluid. Automatic transmission fluid is also very flammable and deteriorates bushings and rubber suspension components quickly. It is very unwise to leave transmission leaks unattended.
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  103. What is the difference in a transmission flush and a service?

    The transmission flush has become very popular with shops. It is highly profitable, does not require much skill and there are no filters to stock. In effect, clean fluid is circulated through the transmission. I feel this does little good and can cause harm. Worse, a generic fluid may be used, rather than the specific fluid recommended by the manufacturer.

    Another problem is, the filter is not addressed. If it were dirty or restricted before the flush it will be at least as dirty after. Flushing may also dislodge debris in the pan and further restrict the filter.

    With proper service, the vehicle is test driven and any symptoms noted. Next the pan is removed, if so equipped and the filter replaced. This step gives a trained technician the opportunity to check for problems. It also allows for a band adjustment, re-torque of valve body bolts or other things that can prevent problem. Finally the transmission is filled with the vehicle manufacturer recommended fluid.

    For much more on proper transmission service, see our article Transmissions and proper service.
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  104. What is the harm of driving with a bad U-joint?

    The harm would depend on the nature of the U-joint failure. Like most parts, U-joints can fail in a number of ways. Deterioration of the rollers results in slack. This produces a clunk when moving between gears. The harm is the sudden shock to the driveline when the slack is taken up.

    Seized rollers may show no slack at all, but make the shaft difficult to rotate. This often shows up as a vibration. The shaking can damage the output area of the transmission and the input area of the rear differential. Seized U-joints can also damage the driveshaft by causing wear in the yokes.
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  105. What is the normal life of rear axle bearings?

    Rear axle bearings can last the life of the vehicle, well over 250,000 miles when properly lubricated. Lubrication of the rear axle bearings is a function of oil level and condition in the rear differential. Even small leaks should be addressed immediately. Fluid level should be checked whenever there is a sign of a leak. Differential oil should also be replaced at recommended intervals.

    See our Detailed Topic Rear Axle Bearing Failure for more information.
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  106. What makes a C. V. joint fail?

    Constant velocity [C.V.] joints fail in numerous ways and for numerous reasons. The most common is a worn outer joint that produces the characteristic click-click-click when turning sharply. Lack of lubrication and debris entering the joint, caused by a torn boot is the leading cause.

    Inner joints also wear and often produce a vibration on acceleration. This can also result from a torn inner boot or wear and tear. Joints also break or pull apart. This is normally caused by mechanical misalignment between the trans-axle and the drive wheels. Causes range from broken motor mounts to a frame or unibody.
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  107. What should I do if my automatic transmission fluid is dark?

    Automatic transmission fluid tends to darken with age and heat. It can also be an indication of an internal transmission problem, but not necessarily. If the fluid is NOT black or smells burnt a proper transmission service may be all that is needed. If it does smell burnt, more serious problems are fairly likely.

    Please see our Detailed Topic Dark Automatic Transmission Fluid for more information.
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  108. When driving my engine seems to be racing. I had the automatic transmission checked and there was no problem. Any ideas?

    Engine sound is a very unreliable gauge of engine speed. Quite often folks come in thinking they have a slipping transmission, only to find there fan clutch is seized. The noise from the fan makes the engine sound like it is running much faster than it is. A better guide is the tachometer and speedometer. If the engine RPM increases significantly, without an increase in MPH, transmission slippage is fairly likely.

    For more on diagnosing transmission problems, see our article Transmission Problems?.
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  109. When my transmission was serviced, a piece of a snap ring and some metal was found in the pan. It still works fine, should I be concerned?

    A broken snap ring may allow the part it is supposed to retain to move. This can cause parts to rub together and create more metal. Worse still, if another part of the ring becomes lodged between rotating gear teeth, the results could be catastrophic. Odds are, repair at this time would be relatively minimal. Waiting for a failure, may cost a lot more as well as the inconvenience of a breakdown.
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  110. Where does the slop in my Ford rear end come from?

    Slop or excessive slack can occur in any rear differential. Excessive clearance between components is usually a result of wear. As bearings and/or gear wear slack develops. The normal symptom is a loud clunk when shifting in and out of gear.

    In my experience, many Ford rear differentials seem to have excessive movement in the spider gears. This can be from worn spider gears and shaft or a worn differential carrier case.
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  111. Why do you think some manufacturers do not recommend automatic transmission service?

    Primarily, because it does not benefit the manufacturer. I think there are several reasons they may feel it is not in their best interest.

    • By omitting recommended services, the maintenance cost is made to appear lower. In reality, this cost is not projected beyond 100K miles, where problems are likely to occur
    • Manufacturers are in the business of selling new vehicles. A major repair, such as a transmission failure, will drive many people to a new vehicle
    • A dealership that improperly performs a service could cause a warranty issue which will cost money to correct. It is unlikely a transmission will fail within the warranty period, even without a service
    • If a problem, without symptoms is found during a service, warranty cost will increase. For instance metal in the pan can signal a transmission that will fail, possibly long after the warranty expires. Not finding the problem until after the warranty expires cost nothing


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  112. Why is my shifter stuck in park?

    The most common cause is a malfunction of the brake/shift interlock system. This system is to prevent the vehicle being shifted out of park without the brakes applied. When the system malfunctions, the shifter may lock in park. There are usually procedures to bypass the system. Check the owner manual for the vehicle for instructions.

    For more information, please see our Detailed Topic, How To Release A Shifter Stuck In Park.


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  113. Why is transmission fluid red?

    The red color is a dye added to the fluid for identification purposes only. Without the dye transmission fluid would be clear to slightly amber in color.
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  114. Why would a new transmission pan gasket leak?

    A leading cause of leakage is over-tightening. Tightening the bolts too much can distort the pan and squeeze the gasket until it tears. Once the pan is distorted it may continue to leak, even with a new gasket. Using sealer on transmission pan gaskets is unnecessary and can also cause leaks. The pan and transmission rail surfaces should be clean and dry when the gasket is installed.
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  115. Why would an automatic transmission move while in neutral?

    A slight creeping on level ground, with no other symptoms may be no cause for concern. Some transmission are fitted tightly and will exhibit a slight creep in neutral. If the problem is more pronounced, such as rolling or gaining speed in neutral, a cross-leak, damaged valve body or clutches are a few possible causes.
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  116. Why would my vehicle roll after being put in park?

    If the movement was slight and then the vehicle went into park, it may be normal. The park pawl that locks the output shaft has to engage the park gear. If the tooth of the pawl does not line up with a slot in the park gear, the shaft may rotate until it does. The pawl is spring loaded and will engage the first available tooth in the park gear. If the park function does not lock, the park mechanism likely has damage or the shift linkage may not be engaging park.

    Park gear and parking pawl operation.
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  117. Why would RPM increase but the vehicle not move when in drive?

    If RPM freely increases, as though the vehicle were still in park, chances are good there is a transmission problem. Transmission fluid may be low, a broken driveshaft or internal transmission failure, among other things can cause such a problem. The engine may also rev up, but feel as though it is in a strain. This could indicate something preventing the wheels from turning. Possible causes could be, the brakes locked up or a wheel seized, due to a bearing failure or differential problem.
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  118. Why would the flexplate, on my engine, suddenly break?

    The actual breakage may seem sudden, but the causes normally have been going on for some time. A flexplate will often crack because of misalignment between the engine and transmission. Loose mounting bolts, missing alignment dowels and foreign items caught between the two are common causes.

    For a detailed explanation of the problem, please see What Causes a Flexplate to Crack.


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  119. Why would transmission temperature go up when towing?

    Temperature is directly related to load and increasing the vehicle load will increase the temperature. Within limits, this is to be expected. More than fifteen degrees Fahrenheit is normally cause for concern. As load limits are approached this will become far more critical as slippage will drastically increase temperature. Increased transmission temperature is a symptom which indicates a problem.
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  120. Will over tightening my transmission pan cause it to leak?

    Over tightening is a leading cause of transmission pan leakage. The bolts have a specific torque specification that varies greatly from one vehicle to another. Exceeding the proper torque squeezes the gasket out of place, permanently destroying it. Over tightening transmission pan bolts can also distort the pan causing it to continue to leak, even when the gasket is replaced. The mount surface should be checked with a straight edge. Any distortion should be straightened or the pan replaced before reuse.
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  121. Will servicing my automatic transmission keep it from failing?

    Properly servicing an automatic transmission can greatly reduce the chances of many types of failure. For instance lubrication related failures, those caused by debris and those caused by restricted filters. It cannot prevent electrical failures nor mechanical part breakage.
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