Gotta question, My brake pedal was soft and I am able to depress it to the firewall, I checked the fluid reservoir, empty. I refilled it and found a leak between the mastercylinder and the vacuum booster. Should I just replace the gasket(928 355 819 00) or replace the master cylinder?

Ted Lavizzo
1987 928s4 Diamantblau Metallic A/T
WP0JB929HS860563 132796mls
PCA
Great Lakes Owners Club
928OC

 

There shouldn't be any fluid in between there to leak. Fluid in there is usually a sign of a failed booster rather than a failed master cylinder.

Pull the master cylinder off the booster and get all the fluid out. There's a check valve on the booster that should hold enough for two or three stops, after the engine has shut down. With the master cylinder reinstalled, start the engine, shut it off, and then come back in a few hours and see if tere's still enough stored vacuum to boost your pedal effort. If not, a new booster may be in your future.

 

Hi it sounds like the master cylinder has started leaking just replacing the gasket wont fix things get a new master, clean out the booster , bleed master first then do all of the wheels , i would suggest you use ATE super blue racing fluid, made for the ATE brake system on your car.

 

If there is brake fluid in the brake booster that is a sign that the secondary cup on the primary piston of the master cylinder is leaking. Suction out the fluid in the brake booster and get a new master cylinder. My suggestion would be to buy it online fron Kragen's. Best price and get the one rebuilt by Cardone. It comes with installation instructions and a bench bleeding kit.

 

Sounds more like the grommets between the reservoir and the m/cyl have died (turned into gum) and the fluid is running along the underside of the cylinder - mine was like this when I got it. They are same as fitted to many MB brakes, made by ATE IIRC, couple of $ tops. Booster filling with fluid will get a VERY hard but ineffective pedal after a while.
jp 83 Euro S AT 50k

 

To all who answered this, I do very much appreciate your insite and recommendation to resolve this issue.
Ted Lavizzo
1987 Daimantblau Metallic
PCA-Chicago
928OC
GLOC

 

The brake fluid in the booster quickly attacks the rubber inside and drastically reduces it's life. Did you not get a low brake fluid warning light and or Brake Press light ?