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Old 11-30-2016, 11:19 PM
#TRUMP2020
 
Join Date: Jun 2012
Location: Virginia
Posts: 789
w210 turbodiesel, hard brake pedal after engine off

Hello, I have a 1998 E300 turbodiesel with a bizarre braking problem.

With the engine running, the brake pedal feels normal, doesn't require much effort to push, braking performance is fine. It feels totally normal.

After I shut the engine off, the brake pedal turns into a rock. You cannot push it down, not even a little bit. Upon starting the engine again, the brake pedal goes back to its normal feeling regular state.

In a healthy car, engine off, if you pump the brake pedal a few times, it slowly becomes stiffer and stiffer until you can no longer depress the pedal. My car feels this way every time you shut the engine off - it goes directly to the rock hard state without pumping the pedal.

Sounds like some kind of weird vacuum issue, but the fact that everything feels normal and fine with engine running has me stumped.

Any ideas on what to check are much appreciated.

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  #2  
Old 11-30-2016, 11:20 PM
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Join Date: May 2016
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You likely have either a failing brake booster (the rubber diaphragm can develop tears or cracks) or you have a failed check valve in the brake booster vacuum line. Either one will allow the vacuum to bleed off when the engine stops.
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Old 11-30-2016, 11:58 PM
#TRUMP2020
 
Join Date: Jun 2012
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Quote:
Originally Posted by Diseasel300 View Post
You likely have either a failing brake booster (the rubber diaphragm can develop tears or cracks) or you have a failed check valve in the brake booster vacuum line. Either one will allow the vacuum to bleed off when the engine stops.
That makes sense, thanks. I believe the check valve is integral with the booster vacuum line. This is cheaper and easier to replace than the booster, so I'll do this one first. Now to try and find a part number...

Edit: found it, 210 430 37 29

Last edited by torsionbar; 12-01-2016 at 12:22 AM.
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Old 12-30-2016, 05:36 PM
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Join Date: Jun 2012
Location: Virginia
Posts: 789
Looks like you nailed it Diseasel300 - I replaced the vacuum line from the vacuum pump to the booster and problem is solved! So probably the integrated check valve was faulty.

The part 210 430 37 29 was correct for my 1998 E300, it was a little over $60 from my local dealer.

Another symptom that seemed related, was both of the vacuum modules under the hood (the one next to the glow plug relay, and the one next to the air filter housing) were making a rapid ticking sound for several minutes after shutting the engine off. After replacing this faulty vacuum line, the ticking no longer occurs. Two issues resolved with one part!

The new part had all of the rubber grommets already attached, so it was literally a one part plug-n-play replacement, nothing additional to buy. The only tool required was a 19 mm wrench to R&R the connection at the vacuum pump. Total time was ~10 minutes, a quick fix.
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  #5  
Old 12-30-2016, 06:38 PM
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Cheap and easy replacement parts are always the best!

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