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Tool Talk Discussion Forum

Bleeding Brakes-On Truck With Boost

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pbutler

07-26-2006 07:28:07




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I have a 67 GMC Grain (like a Chevy 60) truck with brake boost on it. I took it out last week (after sitting all winter) and failed to check the master cylinder-so now the lines are full of air.

I have never bled the brakes on this truck-when truck isn't running the pedal is stiff-but when I start it you can almost push it to the floor.

Question is when I bleed the brakes do I need to have it running?

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Hobo,NC

07-27-2006 15:48:49




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 Re: Bleeding Brakes-On Truck With Boost in reply to pbutler, 07-26-2006 07:28:07  
that�s one truck that I have had issues with. You can clamp off each brake line till you find the wheel that has air trapped in it and werk on that wheel. To git the air out of this system git you garden sprayer out and clean it good and dry. Pour your brake fluid in it you will need at least 2 qts. Drain the master cyl of fluid. remove t the sprayer end add a hose and hook to the bleeder and crack the bleeder now give the sprayer a pump of to to force the fluid back thru the system into the master cyl. You can also werk from the master cly either take the lines loose and force fluid thru the system or try and force the fluid thru the feed holes in the master cly. I like to just unhook the lines at the master hook the sprayer up to'em and do it that way then conect�em back up leave loose and have sumone press the pedal slowly while I thighen�em up. For sum reason pump�in the pedal will not git the air out. I also will after a test drive have someone press the brake pedal while I crack each bleeder. DO NOT PUMP the pedal. Some chebbys are hard to git the air out of the system it could be air gits by the seals of the wheel cyl, pump�in the brakes agitates the fluid. I do most of the bleed�in by myself and gravity bleed�in werks most of the time but not on a 60�s 2 ton trucks. Even the � ton pick�em ups kin be a bear to git the air out of the rear. I also remove the bleeders and either apply pipe dope, Teflon tape, or anti zees to em so air kin not be drawn past the threads of the bleeder. Their also may be a bleeder on the booster bleed it first then werk out, RR, LR,RF,LF wheel

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MN Scott

07-27-2006 07:00:28




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 Re: Bleeding Brakes-On Truck With Boost in reply to pbutler, 07-26-2006 07:28:07  
One tip from the GM service manual, Do not try to bleed these boosters with the engine running it can damage the internal seals. I have two GM grain trucks of this vintage and I have did brake work on both of them. You most likelly have leaky wheel cylinders that should be replaced. Don't waste time trying to rebuild them just buy new only about $35 each. I use the gravity method to bleed mine, it works good. Start with the bleeder on the booster then the back wheels to the fronts. Its really a simple brake system to fix you just have to deal with heavy wheels and rusty components.

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oldrustycars

07-26-2006 21:20:08




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 Re: Bleeding Brakes-On Truck With Boost in reply to pbutler, 07-26-2006 07:28:07  
if this is the type with the big vacuum booster on the left framerail, under the door, good luck. these can be a real pain. the mity-vac is the best bet, short of a $500 diaphram pressure bleeder



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HWPa

07-26-2006 13:57:28




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 Re: Bleeding Brakes-On Truck With Boost in reply to pbutler, 07-26-2006 07:28:07  
You can gravity bleed the system. Fill the resivoir full. keep the lid off, open all the bleeders and close them each as they stop bubbling when the fluid comes out.keep an eye on the master cylinder keeping it full. The one at the drivers front side should be the one to start seeping first. (Don"t be afraid to open them up a few turns). Look for a wet spot on the wheel cylinders and/or lines,that is where your fluid leak may be. (ASE brake mechanic for years) GOOD LUCK :)

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pbutler

07-26-2006 19:14:42




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 Re: Bleeding Brakes-On Truck With Boost in reply to HWPa, 07-26-2006 13:57:28  
Thanks!



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Tom in Central Pa

07-26-2006 11:51:37




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 Re: Bleeding Brakes-On Truck With Boost in reply to pbutler, 07-26-2006 07:28:07  
A Mighty-Vac would be your best bet.
It is a hand held/operated vacuum pump assembly.
It can be bought as a bleeder kit.
A hose is hooked onto the open bleeder screw, the other end is hooked onto a fitting on a sealed "catch" jar. The Mighty-Vac is hooked onto another fitting on the "catch" jar. The jar keeps the fluid out of the Mighty-Vac. As the vacuum is pumped, brake fluid is drawn down all through the system, and into the jar. Refill the reservoir, and do all the wheels.

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Slowpoke

07-28-2006 00:46:36




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 Re: Bleeding Brakes-On Truck With Boost in reply to Tom in Central Pa, 07-26-2006 11:51:37  
Don't use the lightweight tiny jar that comes with the kit... it will fill up fast and get into the hand pump, killing it. It also falls on its side and you will suck the fluid into the pump. Get a sturdy plastic jar like a mayo quart size or bigger. Buy a couple of feed thru fittings with 1/8 hose barbs and install them in the cover. Then connect one line from the bleeder screw and the other to the pump. You can do all 4 cylinders without emptying the jar. Check a hobby shop for the small hose barbs.

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IH2444

07-26-2006 07:38:15




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 Re: Bleeding Brakes-On Truck With Boost in reply to pbutler, 07-26-2006 07:28:07  
I hope you fixed the reason for the brake fluid resivoir being empty.



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