Brake pedal sticking to the floor with delayed release.

[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.

[tinpusher]

Did you get the correct P.valve? There is one for disc/drum and one for disc/disc. I have read somewhere in the past about the wrong P. Valve holding pressure after it’s activated….just throwing stuff out there

[glhx]

I replaced the master cylinder with a new one and bench bled it.
The master cylinder problem is solved and the pedal not returning is solved.

However…….after fixing this. The pedal was back to very soft. It had been like this for a long time now. Long enough to not drive the car for a while.

I replaced everything. Power booster, lines, proportion valve…..calipers all 4 corners.

The pedal was still soft.

I adjusted the parking brake for the rear disc to 1/16” of an inch to activate. You pull it 1/16th and it grabs. I think 1/8th could be ok but I don’t know. I saw where 1/16” was where it should be.

Either way. The parking bakes are adjusted well and I have a very good understanding on how to do that.

So……I still have this soft pedal. I bleed the brakes over and over and over again. The fronts bleed fine. Quickly and done.

The rear passenger  side bleeds fine. Takes a while…..but bleeds fine. No air whatsoever. Not even the smallest bubble.

The drivers side rear however. I bleed it and over and over again small puffs of air keep coming out.
So

I got some Teflon tape and wrapped the bleeder screw very thick so it would seal while being open and not draw air into the threads. I then got some 3/16 clear vinyl tubing and ran the tubes from the open bleeders all the way to the master cylinder.
I did this to both back calipers.

The passenger side……no bubbles.


The  drivers side however…….would not stop pulling air. Pump after pump…..probably 200-300 pumps of circulating fluid. It kept pulling big 1” long bubbles of air over a timed sequence.
As soon as the air was pumped back into the master cylinder. Another 1” of air would come out the tube from the caliper.

So what this means is that my drivers side caliper WONT LEAK FLUID. But will pull in air and not allow me to bleed the system.

With both calipers hooked up at the same time in the back to the 3/16” tubing. It’s only the drivers side that pulls air. I checked all connections and they are tight.
This is a new caliper from O’Reilly.

I have caliper cores so I know what the system looks like and exactly how it works.
I guess…….its pulling in air from one of the 2 seals?

There is a check valve on front of the piston but no fluid is coming out of it. Which I don’t think fluid is ever supposed to come out of it. I think it’s meant to get rid of air behind the piston and not let any back in. I will add that when I took the check valve off. It had some rust under that seal.  Not much but some.

So……I have warrantied out the caliper hoping the new caliper will be sealed.

What do you guys think is acceptable for for inches of travel for an e brake adjustment?
1/16”
1/8th”

And

Why or how do you think that one side is not leaking fluid but is pulling air.

Keep in mind……every part of the system is new. Hoses…..brake lines.

All of it……

It’s just this one caliper and it has cost me about 15 hours to diagnose.

I will add that putting in that clear vinyl tubing and pressing the brake pedal over and over again has helped a lot to figure the problem out and instead of using my pressure bleeder in this car. I will be using this method. As it cycled the fluid over and over until the air was gone
At least in 3 calipers.

If I can get that drivers side to stop pulling air. The system will work to 100% again.

[Wallington]

The correct fitting doesn't need Teflon tape, perhaps the more you add, the more it can't seal.