TAC Tech > Tires, Brakes & Suspension

Brake pedal sticking to the floor with delayed release.

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glhx:
Brake pedal is sticking in the down position after replacing the proportioning valve and lines.

I just replace everything from the booster back.
Calipers, rotors, booster, master cylinder…..
All of it.
I had a soft pedal before all of that. But it wasn’t sticking to the floor until the lines and the p valve.

Now I press the pedal down and have to help it back up. It sinks to the floor and sticks there. I have to pull it back up with my foot.

The car does stop but not well. I’m not sure what’s causing this.


I will add that when the car is in idle. The pedal return. It’s only when I’m actually running and stopping that it does this.

Wallington:
Several potential reasons, Google will cover most since they are all simply ideas that you need to check to confirm. Generally it's an issue with the master cylinder leaking past the seals, air in the system also as a result of first, leaking seal at a cylinder or caliper. Look for obvious fluids leaks, also look for fluid loss, or gain in reservoir where air has entered the system somewhere and stayed elsewhere. Did you bench bleed the mc before installing? Complete fluid renewal and bled from furthest point forward? Don't drive it until sorted.

tinpusher:
It almost sounds like the seals in the master cylinder were maybe installed backwards?

Maybe the spring in the master cylinder is not correct and too weak to retract the piston?

The only other thing that might cause some kind of fluid lock would be the proportioning vale being offset.. meaning, not using the valve centering too to hold the valve in the correct position while your bleeding the system.

My guess is that you received a bad master cylinder.

tinpusher:
This is the centering tool if your P.valve didn’t come with one.

firebirdparts:
I think it has to be the booster.  The MC is actuated by a little pushrod that doesn't connect, so you couldn't pull the piston back no matter what you do.

Air in the lines would help you (by acting as a spring attached to the piston), so that may be a problem, but it's not "the" problem.

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