Brake pedal sinks in to the floor and the car is not stopping

1991 JEEP WRANGLER

300,000 MILES • 4.2L • 6 CYL • 4WD • MANUAL

EDDY WEBER

MEMBER
1 POST

Brake pedal sinks in to the floor. It doesn't matter if the engine is on or off. Even after pumping the pedal, it is going all the way down and there is no brake action. Not even a little bit. There is no leak in the system, the fluid is full in the reservoir.

Should I buy a new master cylinder or should I buy it with brake booster already? There is no ABS in my car.

Best regards,
Eddy Weber

Jun 5, 2020 at 7:43 PM

DANNY L

✓Experienced Mechanic
5,648 POSTS

Hello, I'm Danny.

Sounds like you might have a problem with just the master cylinder.Possibly internal leak in the master cylinder will give your symptom.Brake booster issue would be the exact opposite with the brakes being rock hard with no pedal movement.Here are tutorials showing what is involved for master cylinder replacement and brake bleeding procedure after the replacement:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

I've attached below picture steps steps below on the master cylinder replacement and bleeding procedures.Bench bleeding is to be performed before installing the master onto the truck.Hope this helps and thanks for using 2CarPros.

Images (Click to enlarge)