Spongy brake pedal when engine running

JOHN WIELAND

MEMBER
2002 CHEVROLET BLAZER
4.3L
V6
2WD
AUTOMATIC
160,000 MILES

Spongy pedal goes to floor! I have replace the master cylinder two times with new ones, the booster, rear calipers, ABS module, have bleed a gallon and a half of dot 3 fluid through it. I have had it to one shop two times and to the dealership and they both did the scan tool bleed for the ABS pump. Have gravity bled ten minutes a wheel pure fluid. I have good pedal until I start the engine. Please is there any help out there?

4 Replies

HARRY P

MECHANIC
2,292 POSTS

Exactly what do you mean by spongy? Does the pedal go to the floor, or just travel further than most other cars. Because the brakes in most Chevrolet trucks are like that. However, it could just be that you need to change the brake fluid. Over the years, with the heating and cooling of the brakes, the fluid can become more compressible. Thus the feeling of sponginess. I would suspect there is air in the lines. These guides can help you fix it.

https://youtu.be/w7gUsj2us0U

and

https://youtu.be/WDxvEQrMkBg

and

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Please run down these guides and report back.

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Friday, March 19th, 2021 AT 11:54 AM

JOHN WIELAND

MEMBER
2 POSTS

Yes the pedal goes to the floor or it feels like a master cylinder bypass you hold the pedal it goes to the floor! After a gallon and a half of fluid bled through it would think it is flushed good clean new fluid coming out on all four wheels.

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Friday, March 19th, 2021 AT 11:55 AM

HARRY P

MECHANIC
2,292 POSTS

Well then I am as stumped as you are. I will say that just standing on it, my 2002 Blazer will go to the floor, eventually. But it stops on a dime when driving, even when suddenly braking hard.

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Friday, March 19th, 2021 AT 11:55 AM

KEN L

MASTER CERTIFIED MECHANIC
47,513 POSTS

Here is what we do, take sets of vise grips and use cardboard to cushion the grip jaws against the rubber brake line and gently close them off. This will help us decide if it is master or wheel related, should have hard pedal. Let us know.

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Please let us know what you find. We are interested to see what it is.

Cheers, Ken

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Friday, March 19th, 2021 AT 11:55 AM