Brake Pedal Travel

meeceboy78 · January 5, 2010

Hello,

before I start i want to let you know that I have searched, but really nothing came up that I found.

My Dad has a 1995 GMC Full size pick up. He has been having issue with the brake pedal going slowly to the floor or near bottoming out. If he is sitting still with the pressure applied to the pedal, it will slowly go down more. almost like it is loosing pressure somewhere, but there are no leaks anywhere. Does anyone know what it might be? also on a cold start it has a squealing sound, but goes away after it warms up. I thought that could be some sort of vacuum leak possibly the cause of the brake pedal going down further than normal.

Any suggestions would be greatly appreciated.

thanks

Ryan

txab · January 5, 2010

Master cylinder

meeceboy78 · January 5, 2010

Master cylinder

what about it? does it need to be replaced? bench bled? what about the booster? do you think that is ok?

thanks

KMGZ400 · January 5, 2010

it probably is shot. the master cylinder on the GMT400s are awful i replaced 2 of them on my old truck

meeceboy78 · January 5, 2010

it probably is shot. the master cylinder on the GMT400s are awful i replaced 2 of them on my old truck

alright, sounds like the master cylinder is the consensus. sorry for the dumb question, I am learning as I go. What is GMT400? is that the style of cylinder for the C/K trucks?

also would you guys recomend a particular brand? would either of you stick with the factory master cylinder?

thanks guys

c4cruiser · January 5, 2010

+2 on the master cylinder. Sounds like an internal leak. When it gets replaced, do a complete brake fluid flush. Should take about a quart to do.

Do you hear any hissing from the brake booster? Usually a bad booster (vacuum leak) results in a hard pedal, not soft.

A squealing sound at startup can be a bad bearing on any one of the rotating pieces driven by the belts. Can also be a belt that has oil or grease on it or has gotten hard because of age. If the belt is original, replace it.

meeceboy78 · January 5, 2010

+2 on the master cylinder. Sounds like an internal leak. When it gets replaced, do a complete brake fluid flush. Should take about a quart to do.

Do you hear any hissing from the brake booster? Usually a bad booster (vacuum leak) results in a hard pedal, not soft.

A squealing sound at startup can be a bad bearing on any one of the rotating pieces driven by the belts. Can also be a belt that has oil or grease on it or has gotten hard because of age. If the belt is original, replace it.

I dont hear any hissing, so thats good...

yea as far as the squealing I was thinking belt tensioner or somthng along those lines.

thanks guys for all the feedback.

2005LT · January 5, 2010

Ryan, the "GMT-###" designation is what we use to differentiate between the different model trucks. If I'm not mistaken, GMT-400 refers to the 88'-98' GM trucks and SUVs, GMT-800 is the 99'-06' models, and GMT-900 is the current 07'-10' trucks.

meeceboy78 · January 5, 2010

Ryan, the "GMT-###" designation is what we use to differentiate between the different model trucks. If I'm not mistaken, GMT-400 refers to the 88'-98' GM trucks and SUVs, GMT-800 is the 99'-06' models, and GMT-900 is the current 07'-10' trucks.

Oh, I see now. thank you for clarifying.

well, my dad just ordered an OEM master cylinder so I will keep you all updated as we go.

he should have it by tomorrow.

thanks

meeceboy78 · January 7, 2010

ok guys,

got the new master cylinder on. Bench bled it and bled the brakes (A LOT)

pedal doesnt slowly creep to the floor anymore but is very spongey. I know that means that there is probably stil air in the system somewhere but we bled it to death. could there be air trapped in the abs module?

Thanks a ton!

Ryan