Brake pedal sinks to floor with truck running or not

NATHAN MORNEAU

MEMBER
2007 GMC YUKON
6.2L
V8
4WD
AUTOMATIC
270,000 MILES

XL Denali auto AWD. Does not build pressure at all. I replaced front calipers, rotors, and pads. Rear calipers and also the master cylinder. Bled the brakes and had some pressure for a couple days but not good at all. Was told to bleed the ABS module. I did that with the truck on blocks and braking to engage the module. After that bled the brakes again. Then something very strange happened. With the wheels off and truck running put it in gear the rear brakes would do their job. The front not only did not work but when I would step on the brake my drivers side front would accelerate quite rapidly. At a total loss as to what is going on there.

1 Reply

WILLIAM CRABTREE

MECHANIC
95 POSTS

Hello,

Sounds like you have been through quite a lot in your troubleshooting! There are a few things that it could be. You must have some air still trapped in the lines. Does your brake or ABS light come on or stay on?

Here is a link to some instructions that may help you:
https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Here is a link on bleeding instructions as well:
https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

Hope this helps! Thanks for using 2CarPros!

William