Brakes soft when car turns on?

1996 JEEP GRAND CHEROKEE

150,000 MILES • V6 • 4WD • AUTOMATIC

EYEVEE

MEMBER
2 POSTS

I recently had to replace all brake pads, calipers, and rotors on my vehicle. Since doing so, I’ve tried bleeding my brakes a few times and each time, when the car is off my brakes seem to have pressure but as soon as the car starts, all pressure is lost, and the pedal becomes incredibly soft/spongy. I don’t understand how to fix this issue. Thank you

Aug 1, 2023 at 4:01 PM

JACOBANDNICKOLAS

✓ASE Certified Mechanic
110,194 POSTS

Hi,

It sounds like you still have air in the system, or the master cylinder is faulty. With the engine off, pump the brakes until you get a good pedal. Then, hold pressure on it for a bit to see if it slowly goes to the floor.

Do the same thing with it running. If the pedal does go to the floor, chances are the master cylinder is bypassing the fluid and is more noticeable with the engine running.

Also, when you bleed the brakes, make sure to start with the right rear, to the left rear, to the right front, and end with the left front. If you look below, I attached the directions from my manual. This is a traditional bleeding procedure.

If the vehicle has abs, then we need a scan tool that can actuate the ABS module to bleed air from the system. That is mentioned in pic 1

Let me know.

Take care,

Joe

See pics below.

Images (Click to enlarge)

Professional Diagram for 2CarPros Members
Click here to log in and view diagram.

Aug 1, 2023 at 10:26 PM

Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.