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semotus
Premium Member
join:2003-08-28
Plano, TX

semotus

Premium Member

[Help] Intermittent brake issue with 1997 Chevy Suburban

A few months ago the brake pedal on my '97 5.7L Chevy Suburban started to feel very firm when braking.

I checked the fluid reservoir and it was full. Put the cap back on and got in the truck, brakes were back to normal. The brakes continued to function normally for 2 - 3 weeks then the issue returned. This pattern has repeated since the issue first began; brakes feel odd, remove and replace reservoir cap, brakes return to normal.

I'm at a loss as to what is going on with this truck and would greatly appreciate any suggestions.

Thank you!
Dodge
Premium Member
join:2002-11-27

Dodge

Premium Member

Sound like you are building up pressure in the system and removing the cap vents it.

semotus
Premium Member
join:2003-08-28
Plano, TX

semotus

Premium Member

Thanks Dodge,

I'm no master mechanic but that was what I thought as well.
Any idea what would cause pressure build up in the brake system?

Thank you!
Dodge
Premium Member
join:2002-11-27

Dodge

Premium Member

I'm not a mechanic, but after your post went to look online as I was curious, and I found some Corvette forums where it seems to be the vacuum problem with the brake booster. Also found some references to GM trucks having the same booster problem. This is not like what you are describing, but may be able to send you in the right direction:
»www.gmfullsize.com/forum ··· ?t=59941
PrntRhd
Premium Member
join:2004-11-03
Fairfield, CA

PrntRhd

Premium Member

said by Dodge:

I'm not a mechanic, but after your post went to look online as I was curious, and I found some Corvette forums where it seems to be the vacuum problem with the brake booster. Also found some references to GM trucks having the same booster problem. This is not like what you are describing, but may be able to send you in the right direction:
»www.gmfullsize.com/forum ··· ?t=59941

I agree entirely.
All it takes is a small fluid leak in the master cylinder that is then dripped into the booster. The brake fluid then kills the diaphragm in the booster and causes a vacuum leak and you loose some brake assist causing a "hard pedal" symptom.
You have to replace the booster and master cylinder together as the existing bad master cylinder will kill a new vacuum booster in short order.

mattmag

join:2000-04-09
NW Illinois

mattmag to semotus

to semotus


I agree the potential for a booster issue is there, however that does not connect with just being able to remove the reservoir cover to temporarily resolve the issue. If the fluid level is staying full, my first reaction would be to replace the reservoir cover with a new one on the chance that the vent above the seal is not working. I'm really perplexed by that.... I have never in my many years of service run into such a situation.

semotus
Premium Member
join:2003-08-28
Plano, TX

semotus

Premium Member

Thank you for the information mattmag. There hasn't been a single instance of low fluid level on any of the occasions that I've removed the reservoir cover. I'm going to replace the cover as you've suggested and hope that the issue is resolved.
semotus

semotus to Dodge

Premium Member

to Dodge
Thank you Dodge for taking the time to research this issue for me. You certainly didn't have to spend your time doing that and I appreciate the effort.
semotus

semotus to PrntRhd

Premium Member

to PrntRhd
Thanks PrntRhd for the suggestion. Big surprise, I'd never heard of this before. Learn something new everyday!