brake master cylinder choices?

[Tismael711]

My brakes has become really soft and i'm able to push it all the way in while trying to brake. Once i pump it...it gets harder and i have brakes. I've checked for leaks but have yet to find one. I check the reservoir and discovered it was empty so the fluid must be going somewhere. When i put new fluid in...i got a few burbs and bubbles....indicating air in the system. I suspect the brake master cylinder and have search for part numbers in an attempt to buy a new or used one. Various sites list two different master cylinders and of course the one for my car, part # 34 311 1 157 206 (production up to 5/88
seems to be unavailable. Will a master cylinder from 6/88 forward, part # 34 311 1 161 866, fit my car? Could it be the brake booster? brake lines? bad calipers? Any help or advice will be appreciated.

[jlevie]

Part 34 311 1 157 206 is the ATE master cylinder used with the ATE booster from 5/87 on. That part is available. Part 34 311 1 161 866 is the Girling master cylinder used from 6/88 with the Girling booster. You can use either the ATE or Griling parts, but the master cylinder and booster need to be from the same manufacturer.

A loss of fluid with no visible leaks means that the master cylinder is leaking fluid into the booster. Brake fluid in the booster will destroy the diaphragm pretty quickly. So the master cylinder and booster both need to be replaced. I always replace the reservoir at the same time. NAPA is a pretty good source for boosters.