deep_uv

I've done the obligatory searches, both here and Pelican. I think I have a brake master cylinder problem.

Symptom: Brakes work fine during use. When I stop at a light holding my foot on the brake pedal, the brake pedal slowly falls toward the floor. I release and re-apply and at first it's solid but then slowly gets mushy. I did the Vacuum booster test where you pump the pedal several times before starting and then start the car with pressure applied to the brake. It gives a little once the engine starts, so I think the vacuum booster is ok. Any thoughts before I pull the trigger on the master cylinder? Thanks in advance.

Amber Gramps

I think you are looking in the right direction. It sounds like the seals or O-rings on the piston in the master cylinder are letting the fluid leak past them and back into the resevour. If you are not loosing fluid it's the master. two bolts two lines and two wires. You may want to replace the brake light switches while in there. good luck.

EDIT: '92 or '80?

deep_uv

Thanks, Doug. It's the '80.

theiceman

you might want to lift your carpets and the wood board and have a peak down by your pedals .. if 'it's wet you will know for sure your seals are shot. . that stuff will also eat the bushings in your pedal cluster if you haven't changed them to the bronze ones.

bleucamaro

Another quickee check is to pump the brakes to get a hard pedal with the car off. Keep applying pressure, the pedal shouldn't drop.

newsboy

Have you bleed the brakes lately? I had a similar problem after doing a brake flush. Did it over, and found some air in the lines, but it solved my problem which was the same as yours.

Mike Murphy

Double check to ensure that the fluid in your reservoir isn't decreasing in volume. If it's not, then it sounds like a master cylinder problem.

Daniel Dudley

FYI, a weak master cyinder can give out unexpectedly, leaving you with no brakes.

Also, Murph is right. a slow leak or a weak MC are about the only things that cause your symptoms.