Shaking during braking is caused by something that is rotating. By far the best suspect is a warped brake rotor. They can be machined to true them up as long as they will still be above the published legal minimum thickness when that machining is completed. If they will be too thin, they will have to be replaced. The good news is rotors today are not horribly expensive. The bad news is a lot of replacements come from China, and they will warp again in about three months. Not to worry though.
When we make parts out of cast iron, we set them aside for three months to "age" before they get their final machining. There is nothing wrong with the quality of Chinese rotors, but when they make them, they cast them, machine them, pack them, and ship them, then they age on your car. Minor warping is common, and one light machining will solve that. Most shops will do that light machining under their in-house warranty. The biggest problems come from crabby customers who insist on getting new rotors under warranty. The same thing will happen to those in three months so they will have the same problem.
Clunking when releasing the brakes when the vehicle is stopped is not something that is caused by worn control arm bushings. Worn bushings can cause a clunk when the brakes are applied while the car is in motion. It is very possible the control arms or bushings did need to be replaced, but I suspect the real cause of the clunk was disturbed while the car was jacked up and the suspension was hanging down. Other service procedures can also shift parts around enough to mask the cause of a noise for a while. The best approach is to have the steering and suspension systems inspected again at a tire and alignment shop, but be sure to describe the symptoms and observations as well as you did here. Too often we jump on the first obvious thing we find, and neglect to keep looking for other problems. In this case, a mechanic might assume all the problems will be solved by just machining the rotors. Warped rotors do not cause noise.
Rotors can warp in two ways. The easiest to understand is "thickness variation", but it is the least common. As the rotor spins, when the thicker section moves through the brake caliper, it pushes the piston back into the caliper's housing. That pushes brake fluid back up which pushes on the brake pedal. You would feel that type of warpage as the brake pedal pulses up and down when you push on it.
"Lateral run out" is more common. The friction surface is no longer perfectly parallel to the mounting surface. You will not feel that in the brake pedal unless it is really bad. You will not even feel it when it is relatively minor, which is quite common. When that type of warpage gets bad enough, it forces the caliper to slide left and right on its mount, once per wheel revolution. At higher speeds, the mass of that caliper getting thrown side to side will tug on the steering linkage and will be felt in the steering wheel. That also will not cause noise, however, if there are worn parts in the steering or suspension systems, those can cause noise from being shaken.
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Wednesday, February 28th, 2018 AT 5:54 PM
