Monday, May 21, 2018 Detailed Auto Topics
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The original vehicle brakes lasted 45,000 miles. Just 5,000 miles after the first "brake job" they are squealing again and now the steering wheel shakes when the brakes are applied.

Shudder on braking is a symptom of a problemNoise and shudder on application are the two leading brake complaints, by a wide margin. Many times they are the result of an improper brake service. Brake shudder is an annoying vibration in the steering wheel when the brakes are applied. It feels a lot like a wheel shimmy, except that it starts when the brakes are applied and quits when they are released. 

The cause of brake shudder is warped brake rotors. When a brake rotor warps, the two faces no longer travel in a straight plane. Instead they wobble from side to side or run in non-parallel planes. When the brake caliper presses the pads against the rotor the motion is transferred into the suspension. This is what the driver experiences as brake shudder; the steering wheel shaking.

The faces of a warped brake rotor wobble side to side

It is important to remember that warped brake rotors are always a symptom of another problem

If the root cause of brake shudder is not found and corrected, the symptom will return

One of the leading causes for warped brake rotors is excessive heat. This can come from a number of things. The three most common are discussed In part one and two.

1. Improper brake pad material

2. Driving style

3. Binding brake calipers

When brake rotors warp, eliminating the cause and then replacing the rotors is the only fix. Replacing the rotor without correcting the cause will not give good results. Even if the cause is corrected, machining the rotor may also give only temporary results. Brake rotor warp occurs because of excess heat. The original brake rotor warped even though it was at full thickness. Machining the rotor removes metal and makes the rotor less able to dissipate heat. After being turned the thinner rotor will only warp quicker than the original.

Aftermarket Brake Pads

Heat cracks, shake on braking and noise from cheap pads

Original equipment brake pads are designed specifically for the vehicle on which they are installed. Even on the same year, make and model pads can vary. For instance an EX may have a different brake pad than an LX model.

The coefficient of friction, fit and material used must be correct for the application. Aftermarket brake pads are generally a single material, used on multiple applications. In our experience this results in a great many problems.

If the pad does not help to remove heat or if it generates too much heat the rotor will be affected. Small cracks in the face of a rotor, or a blue color to the metal are signs of too much heat. The symptom is a warped rotor and brake shudder.

Poorly fitting pad cost expensive rework

Sometimes aftermarket pads do not fit properly. They may be too loose in the caliper mount. When this happens there will be brake noise. Noise is the result of vibration. If the pads do not fit tightly or if they are not properly lubricated, there will be noise.

There are also several clips, springs and/or pad shims that are used to reduce noise. Many times aftermarket brake pads do not have provisions for the pad shims. If the shims are disposed of, they will have to be replaced when the job is redone to correct the noise. This adds even more cost and time to the job of correcting the problem.

Occasionally even original equipment brake pads can have a problem. When this occurs the manufacturer will normally issue an updated pad set. Quality shops will keep up with technical service bulletins (TSB) and always check for an updated pad.

Driving Style

Driving style can involve several things. Brakes work by friction and friction produces heat. They are designed to self cool under normal conditions. This takes several minutes and even after cooling they are still very hot.

 Driving through standing water will quench the hot rotors and cause them to warp. It is best to avoid standing water, but if it cannot be avoided allow time for the brakes to cool before driving through.

 Hard braking generates considerably more heat than easy braking. Stopping short and not allowing the vehicle to coast to a stop will wear brakes very quickly and warps rotors.

 Riding the brakes also has much the same effect. Even very light pressure on the pedal will cause the brakes to drag and produce tremendous heat.

 Brake rotors operate at high temperature and require time to cool. Anticipating stops and coasting will greatly reduce brake wear, noise and warping of brake rotors.

In part-two, next week brake caliper problems and other concerns will be covered. Thanks for reading.





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