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Discussion Starter #1
I have had my '82 for a year now and have used benzworld many times to solve little mysteries with the car, but this my first post.

Last week after a 100 mile drive the car wouldn't shut off and the brakes got really hard. At first I was mystified but after reading various posts learned the two are connected and that it is likely a vacuum problem. Haven't traced the source yet but that's not why I'm writing.

What also happened at the exact same time was a huge increase in performance. No more dragging away from stop signs or leaving clouds of black smoke when I press on the pedal. The performance is so much better that I'm tempted to live with no brakes and manual shutoff.

Just kidding but seriously what I hope someone can explain to me is the connection between brakes/shutoff and the performance improvement and how I can avoid reverting back to the bad performance by fixing the shutoff and brakes.
 

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W124 400E, W126 500SE
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There is a vacuum pump on the engine, and it is connected via gear directly to the camshaft. Is it possible it was shot before and made a huge hit on performance, until it gave up now?
How long have you had the car?

Vacuum also governs turbo AFAIK (I only had diesels, no turbodiesel), so it can be related.

Beware, that when this part seizes, it has the ability to strip the gears and snap the camshaft...
 

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Discussion Starter #4
Thank you both for your thoughts. I checked my lines today and the vacuum pump is working fine, the brake booster is the problem. Still can't understand why the power boost unless the change in vacuum triggered some other component to work differently. My first thought was ALDA, but that isn't tied into the vacuum system at all, is it?
 

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1983 300 SD, 1991 420 SEL, 1979 300SD
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the ALDA is not tied to the vaccum system; the line going to it comes from the intake manifold and supplies pressure from the turbo. the only other thing that the vacuum line connects to is the transmission modulator (via the Vaccuum Control valve (vcv) on the IP) and the EGR . i'm guessing the vacuum problem is making your transmission shift differently. inspect the check valve just before the booster to make sure it's not the problem. if it is indeed the booster than it will leak large amounts of vacuum which could explain the no shut-off situation
 

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'82 Euro 500SEL, '85 Euro 500SEC AMG WB Cabriolet,'86 Euro 500SEC RUF
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May be just the check valve in the brake booster line. if it is bad you are not holding vacuum so the booster doesn't work, hence the hard brakes. I would check the Vacuum line and the check valve. If you can blow back through the check valve, then it is no good. Check valve allows vacuum in but not back into the line, that is what makes the booster work like it is suppose to.
You cannot buy just the check valve and you have to buy the whole line.
 
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