Brake pedal goes to the floor Master cylinder and bled the system

GREENSTONE

MEMBER
2004 JEEP GRAND CHEROKEE
4.7L
V8
4WD
AUTOMATIC
120,000 MILES

Last year, December 2016 we replaced the master cylinder and bled the system. At this point the pedal back at the normal position. A month later, January 2017 when the freezing time come, the problem back, pedal flooring again. We replaced the master cylinder again and bleed all the system again. The pedal back in a normal function. I had a good break until the freezing time came back in December 2017. The problem was back, pedal flooring again. About ten months with a good pedal.

The two master cylinders that I bought were an after market the original is very expensive. Not the first time that I use the after market and never got problem with it before today if it is the issue.

There is no leak in the system cause the liquid has been full all the time, I never had to add liquid.

When the motor do not run, I press the pedal and it is up and hard, I keep the pressure on it, start the motor and it go to the floor.

I tested the ABS controler : When I run on slipprery road
(snow or ice) I must pump one or two time, pedal is at the haft way and I can ear the ABS in fonction with the wear sound as we know and the vibration in the pedal

A bit discourage with this issue.

Thanks so much for your advise.

Maurice

3 Replies

HARRY P

MECHANIC
2,292 POSTS

The seals in the new master cylinders are shrinking when it gets cold. This happens, it is part of getting aftermarket master cylinders sometimes. Get another master cylinder and change it. Let us know how it goes for you.

PS. The brake pedal is hard when the engine is not running because you are getting no help from the brake booster, which only works when the engine is running. You start the car, and the pedal sinks because the booster is kicking in and doing its thing.