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Brake Clunk A Real Mystery

posted by  jdbs3 on  Fri Oct 22 07:46 CST 2010
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last visit: Mon Jul 14 15:19 CST 2014
[RELATED]

240 DL Sedan, 150K miles

The cars makes all types of creaking noises, so I’m not sure how long this *problem* has existed.

Basically, I here a single clunk every time I apply the brakes regardless of speed. The clunk does not continue as long as I don’t take my foot off the brake. And the car does not pull to one side or another while braking.

If I pumped the brakes, I would get the clunk every time I hit the brake peddle. Yet it does not happen if the brake peddle is hit when the car is at rest.

I also just noticed that it did not seem to happen when I backed up in a parking lot. Curious I went to a safe area of the parking lot and experimented. If I went forward and put the car in neutral, then the clunk occurred, as expected, every time I hit the brake peddle.

However, if I go backward, put the car in neutral and coasted, then it sometimes happened on the first tap of the brake peddle, but did not happen on subsequent taps on the brake peddle.

I tried this a few times just to assure the above was correct.

It’s unclear where the noise is coming from. It sounds like the rear, but then again possible the front.

The front brakes, rotors, calipers are all new, the rear brake pads are old, but good.

Any thoughts on what might be causing this clunk?







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    Brake Clunk A Real Mystery

    posted by  TONY H on  Sun Oct 24 04:49 CST 2010
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    last visit: Fri Oct 17 16:39 CST 2014
    [RELATED]

    I would check your Torque Rod Bushings.
    Sounds like the rear axle is rotating a bit because the Bushings are bad. The rubber in the bushings can be worn out so it only Clunks in one direction.
    --
    '75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html








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    Brake Clunk A Real Mystery

    posted by  Will740turbo on  Fri Oct 22 18:39 CST 2010
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    last visit: Wed Oct 22 16:09 CST 2014
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    I'd make sure that your capiler bolts are torque down completely. You might also add some caliper pin grease to the BACK of your brake pads. It might be enough to stop or reduce the clunk.

    Clunks can come from anywhere in your suspension and various parts of your car... Check the basics first, like loose lugnuts.
    You can go out, jack up your car and whale on the tires back and forth. If you want, you can use a prop rod to keep the brakes held down and simulate the brakes being on. That might help you localize the noise and start working on it.

    Happy Bricking and Good Luck
    --
    1990 740 Turbo, on its way to stock specs, maybe beyond








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    Brake Clunk A Real Mystery

    posted by  Chris Mullet on  Fri Oct 22 09:28 CST 2010
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    last visit: Fri Oct 24 09:08 CST 2014
    [RELATED]

    It may be the front strut rod bushings. When they get bad enough you can grab a hold of one of the front wheels and vigorously pull it fore and aft and feel the play.








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      Brake Clunk A Real Mystery

      posted by  jdbs3 on  Fri Nov 5 07:43 CST 2010
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      last visit: Mon Jul 14 15:19 CST 2014
      [RELATED]

      Took the car to my mechanic this am. The sound was easily reproducible; he thought it was coming from the front end.

      On the initial pass, there were no loose bolts, and all front end bushings looked ok. When his partner got in the car on the lift and hit the brakes while he spun the tire, we could see the new brake pads moving slightly in the rebuilt calipers. That might be the problem, but it wasn't.

      On closer inspection, though the caliper bolts were tight, we could see the right caliper moving around the bolt when he would rock the wheel back and forth with some pressure on the brakes.

      He tool the caliper bolt out; it looked ok, though the last few threads were clean. He felt the bolt was not bottoming out (I think I go that correct). The threads on the inside of the caliper looked ok, so he took a tap and cleaned out the caliper threads. He did the same for the other caliper bolts on both sides.

      Reinstalled the bolts and success, the noise is gone.

      He noted that the slight play in the brake pads in the caliper was ok; that there was just more space around the edges of the brake pads where they slip into the calipers probably due to the manufacturer cleaning rust off the original calipers. He did suggest some fixes for this, but it did not seem worth the effort from the conversation.

      As an aside, I also noted to him that there was lots of clunks from the rear going over bumpy roads; lots of those in NE. Turns out the torque rod bushings need to be replaced on both sides.

      I'd do this myself, but getting too cold and just not enough hours in the day right now.

      Thanks for the help from all.








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    Brake Clunk A Real Mystery

    uid 5322's pic
    posted by  alschnertz on  Fri Oct 22 08:19 CST 2010
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    last visit: Fri Oct 24 10:32 CST 2014
    [RELATED]

    My first guess would be that the brake pads are slightly smaller than the area in the caliper into which they fit. Then they slightly shift when you apply the brake. We're only talking a few thousandths, but that's all it takes to make the noise.

    My 745 has done this for years within ten thousand miles or so of putting new pads in front. They've always been aftermarket pads (PBR & AXISS). Maybe factory pads would not do it.

    I'd first suspect the brake pads before going into anything deeper like driveshaft, transmission or rear end components. Not saying it can't be them, just not where I'd start.

    You really should post this in the 200 series forum too. You will get more responses.






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