Brake problems!! Need Advise. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bcj67chevy · 04-14-2010, 01:12 PM

hey guys,
Just got a 1972 chevy 4x4 w/ power brakes and front disc. Truck doesn't stop well at all. The pedal is rock hard from the beginning and doesn't seem to go down very far. Would this be the booster and or master cylinder, or could it just be air in the brake lines? Had the front wheels off and the brakes look good.
Hopefully one of you guys ran into this before.

Thanks
Bryan

Wrenchbender Ret · 04-14-2010, 04:43 PM

With the engine off pump the brakes 2-3 times. Then hold pressure on the pedal & start the engine. The pedal should drop a little. Seems like you are not getting vacuum to the booster or the booster is bad. It's not air in the system, that would cause a low pedal. Pull the check valve out of the booster. With the engine off you should get a short sucking noise. When you start the engine ther should be a strong vacuum at the checkvalve & the engine will run rough &/or fast. It's possible you have the adjustment on the rod between the MC & booster too long.

bcj67chevy · 04-15-2010, 07:35 AM

Thanks a lot for the help. looks like the vac hose to the pcv was off, this was hooked up in the same port as the booster.
Thanks guys.

Murphy IRE · 04-15-2010, 09:01 AM

I had a similar problem on my '71. Between the PO and me, we replaced everything. The pedal was firm, but it just wasn't stopping the way it should. The final problem were my vacuum lines. The M/C was getting enough vacuum because of all the other holes. Replaced all the old dead hoses and the first time I tested the brakes, I cleared everything off seats. She came to a hard stop!
If you replace the drums on the rear be careful, there are different sizes and different clearances on the back side. Not that I had to make several trips back and forth and get the back clearance machined to work.

04-14-2010, 01:12 PM	#1
bcj67chevy 402 BIG BLOCK Join Date: Mar 2006 Location: McClelland IA Posts: 286	Brake problems!! Need Advise. hey guys, Just got a 1972 chevy 4x4 w/ power brakes and front disc. Truck doesn't stop well at all. The pedal is rock hard from the beginning and doesn't seem to go down very far. Would this be the booster and or master cylinder, or could it just be air in the brake lines? Had the front wheels off and the brakes look good. Hopefully one of you guys ran into this before. Thanks Bryan __________________ 1967 C10 swb 1970 GMC Jimmy 4x4 2005 Chevy tahoe Z71 2001 Chevy impala Last edited by bcj67chevy; 04-14-2010 at 01:13 PM.

04-14-2010, 04:43 PM	#2
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	Re: Brake problems!! Need Advise. With the engine off pump the brakes 2-3 times. Then hold pressure on the pedal & start the engine. The pedal should drop a little. Seems like you are not getting vacuum to the booster or the booster is bad. It's not air in the system, that would cause a low pedal. Pull the check valve out of the booster. With the engine off you should get a short sucking noise. When you start the engine ther should be a strong vacuum at the checkvalve & the engine will run rough &/or fast. It's possible you have the adjustment on the rod between the MC & booster too long.

04-15-2010, 07:35 AM	#3
bcj67chevy 402 BIG BLOCK Join Date: Mar 2006 Location: McClelland IA Posts: 286	Re: Brake problems!! Need Advise. Thanks a lot for the help. looks like the vac hose to the pcv was off, this was hooked up in the same port as the booster. Thanks guys. __________________ 1967 C10 swb 1970 GMC Jimmy 4x4 2005 Chevy tahoe Z71 2001 Chevy impala

04-15-2010, 09:01 AM	#4
Murphy IRE Registered User Join Date: Oct 2009 Location: South Denver Metro, CO Posts: 385	Re: Brake problems!! Need Advise. I had a similar problem on my '71. Between the PO and me, we replaced everything. The pedal was firm, but it just wasn't stopping the way it should. The final problem were my vacuum lines. The M/C was getting enough vacuum because of all the other holes. Replaced all the old dead hoses and the first time I tested the brakes, I cleared everything off seats. She came to a hard stop! If you replace the drums on the rear be careful, there are different sizes and different clearances on the back side. Not that I had to make several trips back and forth and get the back clearance machined to work.



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