brake pedal

[mirage_brat]

i have been having issues with my brakes in my 77 monza. my brake pedal slowly sinks to floor even after i pump up the brakes.

[cjbiagi]

Are you losing any fluid? I would do a visual check at the rear wheel cylinders, front calipers and the brake lines in general. Sometimes the master cylinder will also leak out of the rear seal and run down the front of the booster. If you do not see any signs of external leakage you most likely have a bad master cylinder that is leaking internally and losing pressure. You should also check your rear brake shoe adjustment, if they are not adjusting then you have to use a lot of fluid to operate the rear brakes and that could also cause a low pedal. You can also try bleeding the brakes and see if this helps but most likely you have bad master cylinder.

[RamIt]

Sinking pedal is a classic symptom of master cylinder failure.

[mirage_brat]

it holds pressure when the engine is off but not when its running

[cosvega76]

With the engine running you're able to increase pressure to the system. It still could be a bad master, although tapered brake pad linings could also be a problem. If you keep your foot on the pedal, will it keep sinking all the way to the floor, or will it stop at some point?

Chuck