On my 90 (125k), I just replaced the front brake calipers. Both before and after the brake job, on every 1 in 20 or 30 stops I have a problem with the brake pedal slowing declining towards the floor. Nothing to the point of needing to pump it or inability to stay stopped at a light, but yes a gentle need for additional pressure on the pedal. Two questions: 1) this is mostly like a MC problem and it should be replaced?

And second: on visually inspecting the MC unit, the servo has some corrosion (pic attached) underneath where it attaches to the MC. I have no brake fluid loss overtime from the reservoir. Is this corrosion normal on a car of this age? And if I replace the MC, what is peoples opinion on replacing the servo as well? Necessary? Nice if you can, but replacing the MC will stop whatever slow leak there is? Or is it possible that brake pedal fade is connected to corrosion somehow?

 

When the pedal slowly & smoothly sinks to the floor under light pressure, that's classic for a MC problem. The piston seals leak back into the reservoir so you don't get any visible leakage.

As far as the corrosion on the vacuum booster, I don't think that's related. However, eventually when that corrosion breaks through I think it'll cause a vacuum leak for the engine, not a brake-fluid leak.

 

Thanks, Jim. Going to bust to open this week and replace the MC and throw some rust converter on the corrosion.