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spongy brake pedal / poor braking


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xwrench3
User

Jun 11, 2019, 11:19 AM

Post #1 of 5 (626 views)
spongy brake pedal / poor braking Sign In

so i own a 2000 GMC Jimmy, every year i have to repair something in the brake system. but this is not the routine sticking caliper, worn pads, or any of the other annoying problems i have had. i replaced the master cylinder a couple of years ago, because i had intermittent spongy brake pedal. which is weird, and it has continued to this day, except i bought a new (and larger) utility trailer, which makes matters worse. so after the initial test drive of the new trailer, i realized that this spongy pedal thing was more than that. so parked in the driveway, i SLAMMED ON THE BRAKES, like you would in a real emergency. my reward for doing so was a blown out metal front brake line. which i repaired. i retested in the same manner, and my reward this time was a blown metal rear brake line. UGGH! enough was enough, so i replaced them all. unfortunately, i STILL have a spongy brake pedal, only its at least 3 times worse. i have bled, bled, and bled to my wife's legs are cramping (from pumping the pedal so much. i have also tried vacuum bleeding, and today, pressure bleeding. with no help at all. i am so frustrated, that i would GLADLY let Adam Savage blow this thing into oblivion! the only clue i can come up with now after pressure bleeding (because i can see how the fluid is moving), is that the flow of fluid coming out the rear brakes is very minimal compared to the front. i can not find a proportioning valve, so i believe it must be a part of the ABS. i am a disabled former motorcycle mechanic, and i have done brakes on everything i have owned since i was 16, but i do not have any experience with ABS things. the thing i find strangest is that there has never been a brake light come on ever.


Sidom
Veteran / Moderator
Sidom profile image

Jun 11, 2019, 11:36 AM

Post #2 of 5 (620 views)
Re: spongy brake pedal / poor braking Sign In

I've had some GMs that need to have the ABS unit bled before I got a good pedal. The only way to do this is with a scan tool.


It might not be a bad idea to take it down to a shop that can pressure bleed the system and ABS unit. Also they will check over all you work.


(This post was edited by Sidom on Jun 11, 2019, 11:36 AM)


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jun 11, 2019, 1:57 PM

Post #3 of 5 (606 views)
Re: spongy brake pedal / poor braking Sign In

Sidom is right, many of these have to be electronically bled using a professional scan tool.

Also, I have found that most GM cars have a pedal that feels very spongy when forced if you simply press on the brake when parked but in reality this is normal and the brakes work very well with very little pressure applied.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xwrench3
User

Jun 12, 2019, 11:35 AM

Post #4 of 5 (583 views)
Re: spongy brake pedal / poor braking Sign In

well, i think i got the air out of the system without going to a dealership. but i would really like to know for certain. if i unplug the 60 amp ABS fuse in the power module under the hood. will the system work like a non abs system? i would like to see if all 4 wheels will lock up, which i can not do now, because of the abs. i did get that to actuate, but the braking performance was not stellar.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jun 12, 2019, 12:07 PM

Post #5 of 5 (577 views)
Re: spongy brake pedal / poor braking Sign In

Disconnecting anything in the ABS system will disable the system. Whenever the dash light is on, the system is shut down.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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