Brake pedal dropping to floor

[Aatos]

I replaced the master with a new one and bled the brakes. Alles in ordnung now! ;)

[Aatos]

Duh, the situation became acute today as the pedal goes straight to floor now and there's no vacuum assist. Time to start wrenching...

[Lakis]

Back to the brake reservoir.

I don't agree. I think it's in his brake booster.

[erik325i]

As said by a couple people already, it's a bad master. I've had an e30 that did the same thing with the clutch master cylinder. I could push the clutch and shift just fine, but if I held the clutch down at a stop light, it would slowly start to release and engage the clutch.

[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.

[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.

[gobuffs]

Back to the brake reservoir.

[Lakis]

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

[graphikg]

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

[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.

[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 :(.

[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.

[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.

[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.

[Gnarles]

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