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Discussion Starter · #1 ·
Recently, when stopped I get a very small thump against my foot on the brake pedal every 3-4 seconds. It is very slight, but it is enough that I notice it every time I am stopped. Anyone every had this issue or know what it could be? :dunno:
 

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Somehow the pulsating pedal while standing still points to a vaccum leak for me!

I guess this occured after you had the car in the shop.The vaccum hoses for the brake booster are attached to each bank throttle and go into the brake booster...
Might be something is messed up there...

Just a thought...
 

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Discussion Starter · #5 · (Edited)
It's not nearly as severe as ABS coming on. Maybe another bad symptom following my service..
 

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I wouldn't expect a vacuum issue to lead to such a regular/periodic thump. The vacuum storage in the booster is large enough that a minor vacuum issue upstream should get averaged out. A major vacuum issue would lead to poor running.

From the description in the OP is sounds like something is activating on a regular period and in the case of the M5 the only thing in line between the master cylinder and calipers is the ABS/DSC unit. The hardware used in the E39 has a long history of going haywire and causing all kinds of problems. Most of the the ones that I've seen take down communication on the CANbus, but it's also common to see them activate one (or more) brake circuits and produce symptoms similar to a sticky caliper. Taking that one step further I could see how a fault could result in some feedback through the pedal.

Easiest way to tell would be to disconnect the ABS/DSC module (under the hood, left side), start the car, and see if the pulsing goes away. If it is an issue with the module there are several options out there for rebuild (or replacement). This process will turn on the ABS, DSC, and BRAKE fault lights, but re-connecting the module should turn them off. Make sure that the ignition is OFF when messing with the electrical connection to the module, or better yet, battery negative terminal disconnected.
 

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Easiest way to tell would be to disconnect the ABS/DSC module (under the hood, left side), start the car, and see if the pulsing goes away. If it is an issue with the module there are several options out there for rebuild (or replacement). This process will turn on the ABS, DSC, and BRAKE fault lights, but re-connecting the module should turn them off. Make sure that the ignition is OFF when messing with the electrical connection to the module, or better yet, battery negative terminal disconnected.

Wouldn't just pulling the fuse work?
Regards,
Jerry
 

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Wouldn't just pulling the fuse work?
Regards,
Jerry
It's a couple of fuses / relays and those power other items as well. Better just to pull the plug on the module (easier too).
 

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Discussion Starter · #9 ·
Thanks for the advice AMP. This may or may not be related, but lately I have a squeal coming from my rear passenger side parking brake. These two symptoms arose at the same time. Could just be that it has gotten cold out and the car sat for a few days, the squeal went away after a bit of driving and putting the brake on and rolling a little. My parking brake handle has loosened some too, the bowden cables are new and probably have stretched out.
 

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I had the same symptoms when a wheel sensor was going out.
 
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Discussion Starter · #11 · (Edited)
I had the same symptoms when a wheel sensor was going out.
I found this mentioned in another car thread when searching on Google. Definitely worth looking into also. Are you saying the squeal from my rear parking brake would also be related to the wheel sensor? or just the thump?

May be worth replacing since the sensors are $25 on eBay. Easy DIY.
 
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