power brake problem? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Daves72'GMC · 05-22-2007, 12:30 PM

I have a 72' GMC with power brakes that I just had restored and I drove it home it was fine and now when I press the brake pedal down it goes to the floor and comes back up very slowly and causes the brakes to stick until the pedal comes up. Does anyone have an idea what could be wrong with my brakes?What kind of brake fluid should I use, I was thinking of bleeding the brakes? Thank you.

rikbar · 05-22-2007, 12:44 PM

I would try to bleed them, make sure you know what fluid the person that rebuilt them used, don't want to mix the stuff, can make a mess.

jsbgump · 05-22-2007, 12:45 PM

It should have dot 3 brake fluid. But I would check with he restorer to make sure thats what they used

rlm316 · 05-22-2007, 12:49 PM

It sounds like you have a pressure release problem. You said that you just had the truck restored. Did they replace all of the brake hardware? If not did they clean and flush all of the original components? What type of brake fluid are you using? Sylicone and regular brake fluid are not compatable, the mixture will cause the rubber in the brake system to swell and trap pressure like a check valve. How is the return spring on the foot peddle? Something could even be binding on the shaft/ piston in the master cylinder. There are alot of possibilities but the best course of action would probably be to contact the shop that did the repairs and have them fix the problem. If it showed up after the trip from them to you, if it was me, I would expect them to make it right. Good luck

Daves72'GMC · 05-22-2007, 01:10 PM

I supplied him with dot 3 and just noticed that he gave me back my dot3 and a new bottle not opened yet of synthetic dot 3,If he did mix them what do I need to do with my system?. I don't really want to deal with him anymore and I would have to have the truck towed to his shop which is quite a distance away.

rlm316 · 05-22-2007, 01:32 PM

I understand where you are at with this, but you need to ask him what he did as far as the brakes are concerned. It could save you alot of time and trouble. If he mixwed the fluids you will need to replace all of the rubber lines and probably the wheel cylinders. Blow out the lines ,flush and refill with the fluid that you want to use. Silicon is used for systems that will not see alot of use because it is not hydroscopic like regular fluid.

05-22-2007, 12:30 PM	#1
Daves72'GMC Registered User Join Date: Mar 2003 Location: Asheville, N.C Posts: 952	power brake problem? I have a 72' GMC with power brakes that I just had restored and I drove it home it was fine and now when I press the brake pedal down it goes to the floor and comes back up very slowly and causes the brakes to stick until the pedal comes up. Does anyone have an idea what could be wrong with my brakes?What kind of brake fluid should I use, I was thinking of bleeding the brakes? Thank you.

05-22-2007, 12:44 PM	#2
rikbar Registered User Join Date: Jan 2004 Location: South Dakota Posts: 65	Re: power brake problem? I would try to bleed them, make sure you know what fluid the person that rebuilt them used, don't want to mix the stuff, can make a mess.

05-22-2007, 12:45 PM	#3
jsbgump Gone Fishing Join Date: Aug 2005 Location: Fort Worth, Texas 76135 Posts: 12,361	Re: power brake problem? It should have dot 3 brake fluid. But I would check with he restorer to make sure thats what they used __________________ 68 Chevy Short Fleetside LSX Swap Under Way 3.73 posi 2.5/4 drop Frame of resto has been started 2022 Hyundai Tucson Limited 2019 Chevy Traverse Redline Edition Wifes Ride Build Thread http://67-72chevytrucks.com/vboard/s...=1#post3483616

05-22-2007, 12:49 PM	#4
rlm316 Registered User Join Date: Aug 2006 Location: Woodstown, NJ Posts: 669	Re: power brake problem? It sounds like you have a pressure release problem. You said that you just had the truck restored. Did they replace all of the brake hardware? If not did they clean and flush all of the original components? What type of brake fluid are you using? Sylicone and regular brake fluid are not compatable, the mixture will cause the rubber in the brake system to swell and trap pressure like a check valve. How is the return spring on the foot peddle? Something could even be binding on the shaft/ piston in the master cylinder. There are alot of possibilities but the best course of action would probably be to contact the shop that did the repairs and have them fix the problem. If it showed up after the trip from them to you, if it was me, I would expect them to make it right. Good luck

05-22-2007, 01:10 PM	#5
Daves72'GMC Registered User Join Date: Mar 2003 Location: Asheville, N.C Posts: 952	Re: power brake problem? I supplied him with dot 3 and just noticed that he gave me back my dot3 and a new bottle not opened yet of synthetic dot 3,If he did mix them what do I need to do with my system?. I don't really want to deal with him anymore and I would have to have the truck towed to his shop which is quite a distance away.

05-22-2007, 01:32 PM	#6
rlm316 Registered User Join Date: Aug 2006 Location: Woodstown, NJ Posts: 669	Re: power brake problem? I understand where you are at with this, but you need to ask him what he did as far as the brakes are concerned. It could save you alot of time and trouble. If he mixwed the fluids you will need to replace all of the rubber lines and probably the wheel cylinders. Blow out the lines ,flush and refill with the fluid that you want to use. Silicon is used for systems that will not see alot of use because it is not hydroscopic like regular fluid.



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