2nd Gen Non-Engine/Transmission Brake pedal fades to floor

[DickersonD]

Hey fellas,

The truck in my sig. has a brake problem. When sitting at a red light the brake pedal slowly fades to the floor without me pushing on it any harder,intially just hard enough to hold myself on the hill. Once it gets to the floor the brake light will stay on until the truck is shut off and then started again. The truck will stop fine but I took it in anyway. It was diagnosed as the master cylinder and I need a brake job anyway. It got a new master cylinder,front pads,rear shoes and rear wheel cylinders. Well I just picked it up and it is still doing exactly the same thing,pedal just fades to the floor at a stop with the engine running. You can pump it back up and when you do that the blend door in the a/c loses vacum and closes for about 2 seconds and then reopens. Could this be a vacum problem? thanks in advance for your help.

 

[DF5152]

master cylinder is bad or you have a leak somewhere? are you loosing fluid?

 

[ttbird]

I think our year truck has a vacuum booster on the master cylinder. I can't beleive you got it back and it's still doing the same thing. That sucks. That work wasn't cheap. !!!!!!!!!

 

[DickersonD]

No it wasn't cheap. The master cylinder is a brand new one and it is not a rebuilt and is not leaking.

 

[Dual EE]

Read this thread and see if applies to your situation... .

https://www.turbodieselregister.com/forums/showthread.php?t=120360

 

[Ethdee]

A friend went through the same thing with his hot rod. Replaced the master cylinder to no avail. Replaced the booster, and it's worked perfectly since then. I never knew a bad booster could do that.

 

[DickersonD]

Thanks duelEE,

That is very closer but I feel I never lost the booster function or the pedal was never hard to push it just slowly goes to the floor. The a/c only acts up when you pump the brakes rapidly at idle.

 

[DickersonD]

I took the truck back today and had it bled again. I found out that the master cylinder was bench bled first. The mechanic is going to replace the M/C tommorow and pressure bleed the system. Hope it works.