Intermittent brake pedal going to the floor when braking

PHIL VANA

MEMBER
2006 PONTIAC G6
3.5L
6 CYL
2WD
AUTOMATIC
140,000 MILES

The car stopped but the brake pedal was slowly sinking to the floor while I was stopped for a few weeks. Then they were working perfectly for a couple days. Then the pedal started going straight to the floor and I am not losing any fluid. The brake pedal will be stiff if I pump it when the car is off, then when I start the car the pedal goes to the floor. So, I changed the master cylinder and the brakes are doing the same thing, sinking to the floor. I bench bled the master cylinder.

1 Reply

MOTOR MASTER

MECHANIC
279 POSTS

Hello my name is Dave.

There aren't many things that can cause a sinking brake pedal as you have described. If you are sure you aren't losing any brake fluid and you have replaced the master cylinder, which would be the most likely cause of the symptoms you have described there are a few unusual problems that I have encountered that can cause this issue. One thing to check would be if all your brake calipers are sliding freely, the best way I have found to do this is to slide the caliper open part way almost as if you were replacing the brake pads and then see if the caliper slides freely. The other thing I have run into is a internally ruptured brake hose, the best way I have found to diagnose this is to have an assistant pump the brakes a number of times and hold them hard and then look at all the hoses and see if any of them have swollen. I hope these tips help you track down your issue and if you need any further help please feel free to ask. We are always happy to help. Please keep us up to date on this issue and thank you for using 2CarPros.