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

Tiny
EDDY WEBER
  • MEMBER
  • 1991 JEEP WRANGLER
  • 4.2L
  • 6 CYL
  • 4WD
  • MANUAL
  • 300,000 MILES
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
Saturday, June 6th, 2020 AT 2:43 AM

1 Reply

Tiny
DANNY L
  • 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.
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Monday, March 15th, 2021 AT 1:31 PM

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