Sunday, December 21, 2014 Detailed Auto Topics
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Windshield wipers get very little thought, until it rains. Lack of operation, poor wiping or wont stop working, are all problems that sometimes occur. If they do, this article can help you to understand why.

Except a few extra features, most windshield wipers operate similarly. Turn the switch and they move back and forth, removing water from the viewing area. A variable-speed motor drives the system.

How a windshild wiper transmission works

Wipers need several pieces of linkage to convert motor rotation into the back and forth motion needed by the wipers. The wiper-transmission collectively refers to these mechanisms.

At the base of the windshield, pedestals rotate. The wiper arm attaches to the upper pedestal-shaft. The shaft may be splined or tapered and often has a nut that secures the arm. The lower end of the pedestal attaches to a lever. This lever connects to a linkage, through a pivoting joint. The other end of the linkage connects to an arm, attached to the output shaft of the motor. As the motor turns, the arm pushes the linkage until it moves a half-cycle. At the midpoint of rotation, the direction of force reverses. This produces the characteristic back and forth action of the wipers.

How windshield wipers park

Turning the windshield wipers off does not cause them to stop immediately. Instead, they continue to run until the blades reach the down or park position. This ingenious engineering prevents the driver’s line of sight from being blocked.

basic windshield wiper wiring diagram

The ignition switch supplies electrical power for the wiper motor. Current passes through the wiper control switch and then to the wiper motor. A speed control module may vary the voltage that reaches the motor on some models. Other types use different windings in the motor to control speed.

Within the wiper-motor is another switch, with voltage that bypasses the off-switch. The motor times this device with the full down position. Many use a cam to open the circuit when the motor achieves wiper parking. Turn off the wiper switch and current continues to flow through the park-switch, until the wipers are fully down.

Wipers that will not stop when switched off usually have a failure in this circuit. Well-meaning do-it-yourself repairers often replace the wiper-switch needlessly, for this symptom.

Automatic rain sensing wipers

Vehicle makers equip many newer vehicles with rain sensing wipers. The wiper-switch may be left in the automatic position on these models. When rain hits the windshield, the wipers come on automatically. This may seem very high-tech, but the principle is quite simple.

How rain sensing windshield wipers work

A small electronic module near the top of the windshield is the brain of the rain-sensing system. Multiple light-emitting diodes (LED) transmit infrared beams. The dry surface of the windshield reflects this light. Other chips within the module receive the reflection. The amount of light reflected varies the voltage that flows through this device.

Water acts like a lens when it strikes the windshield. This causes more of the infrared light to travel through the glass. Less reflected light produces a lower voltage. Low voltage flow signals the wipers to turn on. Once wiped, the glass is now dry and reflection increases causing voltage to increase. More voltage signals the wipers to stop. A further refinement measures how long the windshield stays dry and varies the wipe-speed accordingly.

Wiper arms and blades

Worn wiper blades can be dangerous

No system can clean the windshield without a good wiper blade. The rubber in the blades removes the water from the windshield. Over time, the rubber will deteriorate and wear. Worn blades leave streaks and do not remove water very well.

spring loaded and newer one-piece wiper blades

For many years, wiper blades remained almost unchanged. Most windshield wiper blades used a metal support with several spring-loaded arms to keep the rubber portion in contact with the curved glass. Some current designs replace the spring-loaded blades with a solid one-piece wiper blade. The one-piece blades often contour to the glass better. These blades also may last longer than traditional blades. These newer style wiper blades are more expensive, but may be cost effective, if they give longer use.

Many newer vehicles come equipped with the one-piece wiper blades. One-piece replacement blades are available for the older vehicles. This allows older vehicles to use this newer technology. These are simple to install and trying a set will help you decide if they are worth the increased price.

Wiper arm problems

The wiper blade attaches to an arm, which attaches to the wiper transmission. This arm is usually made of steel and gives few problems. Occasionally these arms will bend or twist. This may occur if we start the windshield wipers on a frozen windshield. The windshield wiper may also contact an obstruction and the arm may bend.

Chattering and skipping wiper blades

One symptom of a bent wiper arm is a chattering windshield wiper. Rather than wiping smoothly across the glass, the blade may skip or hop. This is annoying and leaves our vision obscured. If the bend is not too bad, we may be able to straighten the arm. Twisting the flat portion of the arm, with an adjustable wrench may restore blade contact and stop the chatter. In other cases we will need to replace the wiper arm.

A wiper arm quits moving

Another common issue is a wiper arm that quits working. We turn on the windshield wipers, hear the motor run, but the arm does not move. At the base of the wiper arm, many designs have a nut, used to secure the arm to the wiper transmission. This nut may come loose, allowing the arm to remain stationary.

The wiper arm attaching nut may work loose over time

Turn the wipers off and allow them to park. Place the arm in the parked position and tighten the nut to specifications. The torque specification is listed in service data for the vehicle. Many times they use a decorative cover to hide the nut. The cover is removed to access the nut.

It is important to have the wiper arm in the parked position before attempting to tighten the nut. If the wiper transmission is in a rotated position when we attach the arm, it will be out of time with the system. This will cause the blade to travel further than it should and may damage the arm or the paint on the vehicle.

Wiper blade life

Several things contribute to shortened service life. Geographical areas that are very hot or cold are hard on wiper blades. Using the windshield wipers to remove ice and snow will significantly shorten their lives and may damage the motor and linkage. Removing snow and ice before wiping will greatly extend the life of the windshield wipers.

The condition of the windshield also affects wiper blade life. Chips and cracks in the glass will damage the blades. When installing a new windshield, it is a good idea to replace the wiper blades. Grit embedded in old blades can contribute to scratches in the replacement glass.

Do not use wipers on dry or glass, always use the washers with them

Wiping a dry windshield is very hard on the system. Pressing the washers will moisten the glass and greatly reduce the load of the system. This also helps prevent scratching the glass.

Windshield washer problems

Many washer problems are the result of using water, rather than washer fluid. Bacteria can form in the reservoir and clog the system. Washer fluid contains chemicals that prevent this from occurring. Using detergent can also cause problems. High-quality washer fluid contains an antifreeze agent and other things to help protect the system.

Other causes of wiper failure

leaves and debris can plug drains and damage the wiper system

Allowing leaves and debris to collect at the base of the windshield is another big problem. Debris can plug the drains in the cowl area and submerge the wiper motor in the rain buildup. This will usually destroy the motor and often the associated modules in the area.

Leaves that collect in the cowl may also cause damage to the wiper transmission. These components can be difficult to replace and very expensive. Covering this area, when parking under trees is necessary, can help a great deal.

 Replace worn wiper blades

 Keep the cowl area free of debris

 Avoid wiping a dry windshield

 Use only high-quality wiper fluid





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