Hello,
OK, this is what is happening. When I depress the brake pedal, the car's idle becomes erratic.With the brake pedal fully depressed or released, everything is OK. There is a strong suction noise as well from the servo's brake pedal pushrod area when the idle speed is unsteady.
Need advice form you all before I begin ripping it all out

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Nachi11744

Not knowing what car this refers to I can only guess that the power brake booster has a leaking diaphram. The sucking sound at the push rod also indicates a rupture as does the idle change when applying the brakes.

If the car does not have vacuum assisted power brakes I don't have a clue.

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Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

And there's rubber o-ring gasket between the brake master cylinder and servo that's included in the MC repair kit.

Never messed with servo unit, but attacking it from firewall side looks easy.

Hello,
I am very sorry about the lack of info in the post, it is my gasoline engine W115, it does not have a vacuum pump like the US market cars.
The servo only makes the suction noise with the pedal partly depressed, not when released or fully down
Thanks for the replies, looks like it needs a new servo But the brakes work, lots of pedal travel though.
Thanks again.

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Nachi11744

can you put a vacuum on the booster and see if it holds? it might be that it only leaks when the pedal moves too

mike

I have this same (sort of) situation in a 107. The idle definitely changes when the brake is depressed. BUT, the original booster was bad, and I replaced it, but still get the change in idle although the brakes now work well. I am wondering about the check valve. Just a thought.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Hello,
It was the servo, a crack in the main booster rubber diapraghm(sp?), it seems the *normal* failure mode is like that. As the whole assembly is under vacuum when fully *off* or fully *on*, it does not leak.
I split the can open, with two guys levering the front and rear shells to move it to match the slots and indentations
AFAIK, the check valve just holds vacuum for a few applications of brakes without engine vacuum.
A tip I picked up from my old friend, a BMW shop owner. The vacuum hose should rise upward from the intake manifold and then can drop back to the servo vacuum line fitting. This prevents gasoline vapours and *other* nasty stuff like blowby etc. from mucking up the insides of the servo.
Have a good week.

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Nachi11744

when you hit the brakes, its a small and temporary vacuum leak.

on the rx7's pumping the brakes will make the idle all wacky. one application doesnt unless the idle mixture is off

food for thought

mike