Brake pedal dropping to floor

[Aatos]

I'm using a 944 booster and the brakes work fine. The issue is that when waiting on lights etc with foot on brake, after a while the pedal softens and drops closer to the floor. The brakes don't disappear though, you just need to push more.

Has anyone had this problem? I'm suspecting some sort of leak in the booster diaphram but it would be great to get some input before I replace it.

[whodwho]

Shouldn't be related to your booster. If you are not loosing brake fluid then most likely fluid leaking past the piston seals in the master cylinder. It would sink if pressing lightly and would stay if pressing firmly?

[325issguy]

Sounds like you need to try to rebleed your brakes.

[Vince30]

Shouldn't be related to your booster. If you are not loosing brake fluid then most likely fluid leaking past the piston seals in the master cylinder. It would sink if pressing lightly and would stay if pressing firmly?

This is right on

[Gnarles]

Yeah a bad booster would create a stiff brake pedal. Probably the brake master cylinder.

[jahnaboi]

Air within the system. Bleed it properly. RR, LR, RF, LF order. Don't use a pressure bleeder as well. It doesn't generate as much pressure as the pedal does.

[whodwho]

Air in the system would always have a low/soft pedal, his seems to have a full pedal but sinks as he holds pressure on it.

[brokenbimmer533]

I had the same problem with my old car (non e30) and it turned out to be the master cylinder.
As far as not using the pressure bleeder, I bleed my brakes with a pressure bleeder when I redid the whole system last fall and it worked great.

[Aatos]

Shouldn't be related to your booster. If you are not loosing brake fluid then most likely fluid leaking past the piston seals in the master cylinder. It would sink if pressing lightly and would stay if pressing firmly?

After thinking about it for a while I think you're right. Time to order a new master cylinder :(.

[LivingLegend06]

Shouldn't be related to your booster. If you are not loosing brake fluid then most likely fluid leaking past the piston seals in the master cylinder. It would sink if pressing lightly and would stay if pressing firmly?

I had this exact problem. I replaced the master cylinder with a junkyard part and now the brakes are great.

[graphikg]

^^^^^ Thats what I did too. Yay junk.

[Lakis]

SO...Where did all his brake fluid go? Into his booster?

[gobuffs]

Back to the brake reservoir.

[whodwho]

As you press on the brake pedal it presses on the piston in the master cylinder, there are cups and seals on the piston that seal against the bore assisted a bit with the pressure. That's why when they start to fail they can still work under normal braking but slowly sink when you are lightly pressing on the brakes. When the seals start to fail they don't seal as well and brake fluid from in front of the piston/seal on the pressure side is allowed to seep back past the seals to the non pressure side.

[tonywonder]

yeah a bad brake master in my honda cracked one of my rotors. didnt realize the master was the cause until after i got new rotors and pads.