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In Reply to: Here you go: Details. posted by Big-M on May 28, 2001 at 03:46:43:
Sorry to seem picky, but the spelling of braking as "breaking" is a pet peeve of mine, since I am so involved with performance brakes. (See my E39 brake upgrade web pages: FRONT REAR)
about the knocking.. it happens when there is a heavy-sort-of braking... doesnt happen when im reversing though... And it is very clear that the sound comes from the rear part not the front part... My imagination tells me it could be the fact that the pads (When pressing against the disc) while braking, move abit forward/backward due to their dis-fixation as I come to a complete stop with the vehicle. again, this is just my imagination...
It happens continuously ..but when i do "light-braking" i dont hear it at all...
Let me make sure I understand. Under light braking, there is no sound at all. Under heavy braking, there is a clunk.
If you apply the brakes at 80 mph and keep a steady pressure on them, are there repeated clunks all the way down to 0 mph, or is there only a single clunk? In other words, is the clunking rhythmic or is it only one single clunk per application of the brakes? This is important.
If there is a single clunk, then it is possible that the rear pads are shifting when you apply the brakes and the sound you are hearing is the sound of the pad moving from the rear of the caliper to the front. Or, it could be a problem with the parking brake shoes. Here's a shot of the parts involved in the parking brakes:
If the clunking is rhythmic and occurs once per revolution of the wheel, this may indicate a problem with the rear rotor. It could be warped. Or it could be a rear wheel bearing problem.
Does the sound appear to be coming from just one side of the car? Or is it coming from both sides? Or is it impossible to tell? You might be able to isolate the problem by driving with both windows open. Or, if it occurs at low speeds too, you could have someone stand in a parking lot and drive by them, then apply the brakes hard. Do this while passing them on the left, then on the right and see if they can tell which side of the car is generating the sound.
The more you can narrow down the problem, the better the chance that we can find it. There are only so many parts in a brake system and we can find the problem by process of elimination.
Do you have access to a dial indicator to measure the runout of the rear rotors?
Where do you live? If you are anywhere near NJ, I would be glad to help you troubleshoot this problem in person.
Dave Z.
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