Brake pedal sticks to the floor while running

[SBellew]

Background: My wife drives my 99 2WD Tahoe just around town. The other day she told me the brake pedal was going all the way to the floor and it was really hard to stop.

I changed the brake booster and master cylinder. After changing, I bled the brakes with the vehicle off until I had a firm pedal and no air coming from each of the 4 wheels with her doing the pump 3 and hold process.

Then, she drove it to town and back with a decent pedal and good brakes. The next day, she called me at work and told me the brake pedal was stuck and would not release.

She left it sitting further down the driveway and I looked at it over the weekend. With the engine off, it has a decently firm pedal, but when it is running, the pedal goes all the way to the floor and locks. I tried pulling it up with both hands and it was stuck pretty darned well. When I turn the engine off and over the next 30 seconds, the pedal slowly returns to its normal position.

Thinking it may be a bad master cylinder, replaced that and did the whole process again and the same exact thing happened.

I am at a loss on this one guys. Any ideas or experience with this issue?

 

[drakon543]

ive never heard of this happening before. maybe there is something wrong with the booster???

 

[Repeatman]

Do the Brakes get stuck on while this is happening? Also, Important question. Do you have ABS (anti Lock Brakes) ? There might be some air stuck in the lines where the module is.

 

[SBellew]

Do the Brakes get stuck on while this is happening? Also, Important question. Do you have ABS (anti Lock Brakes) ? There might be some air stuck in the lines where the module is.

Yes, the brakes are engaged when this happens and from what I can tell I do have an ABS control module near the master cylinder. The lines go to it from the master cylinder and there is a set of wires going to the same piece so I am assuming that is what it is there.