brakes - The 1947 - Present Chevrolet & GMC Truck Message Board Network

dana b · 12-03-2008, 01:05 PM

Having brake headaches with this 81 GMC. Before we purchased this truck it had been immersed in water & then sat for 4-5 years. So we have had to replace a lot of stuff. We gave it a complete brake job- new everything & bled them really good & several times. Brakes are still mushy. Tried a few other things- someone suggested the splitter was sticking- changed it- still the same- we are thinking the booster maybe? Any suggestions appreciated.

asphaltburner · 12-03-2008, 09:33 PM

Yo!
Booster, or no booster, you should still get a good solid feel to the brake pedal if they've got a solid column of fliud. A bad booster will make a sucking noise when the brakes are applied with engine running.
Did you bench-bleed the master if it was replaced?
Did you bleed the brake lines "two person" or with a suction bleeder at each wheel? Sounds like you're still dealing with air in the fluid column.
Will the brakes "pump up" as you repeatedly apply the pedal? Todd.

dana b · 12-04-2008, 01:40 PM

Quote:

Originally Posted by asphaltburner

Yo!
Booster, or no booster, you should still get a good solid feel to the brake pedal if they've got a solid column of fliud. A bad booster will make a sucking noise when the brakes are applied with engine running.
Did you bench-bleed the master if it was replaced?
Did you bleed the brake lines "two person" or with a suction bleeder at each wheel? Sounds like you're still dealing with air in the fluid column.
Will the brakes "pump up" as you repeatedly apply the pedal? Todd.

Hmm... it really doesn't make a sucking noise. We did the "two person" when bleeding. The brakes do pump up- but then goes to the floor. As for the bench bleed- sorta- but not really. We kinda did it on the truck- not in a vice like we shoulda. I will try that. Thanks.

AceX · 12-03-2008, 09:45 PM

Check the booster as well

asphaltburner · 12-03-2008, 10:17 PM

Yo! AceX!
How do you check your boosters? All I know is to listen for the leaking engine vacuum when the brake is applied, engine running. My '69 F100 has this problem. Is there a slick, easy check?
Todd.

asphaltburner · 12-05-2008, 02:22 AM

Yo!
It's absolutely essential to clear ALL the air from the master cylinder on the bench, since it's so hard to do any other way. You can push the piston in with a punch or screwdriver, and put your fingers over the output holes to release the plunger. Repeat until you get no air at the outputs or inside the bowls. Messy,...although I've seen short pieces of brake line attached to the outputs and bent to return fluid into the bowls (the bent line ends need to be emmersed,...or plugged when the piston is released so they won't suck air)!
And then I install the master (try to plug the outputs as you do so), keep it full, and begin bleeding the pass. rear first until there's no bubbles (even tiny ones). Then driver's rear, then pass. front, driver's front. It's good (with two people) to pump that pedal multiple times, place pressure on it, open the bleeder a bit, and then close the bleeder just before the pedal is all the way down. Takes some coordination, and repetition, but gives great results. If there's ANY pumpup after bleeding (I hate to say it, but), do it again.
I have opened all the bleeders for a day or so before bleeding, and kept the master full, so that gravity could help fill the lines initially, then bled the brakes normally.
All and all, the idea is for the master to suck fluid from each bowl, the pistons to push it through the lines to the bleeders, and never to allow air to suck back in when the pistons are released. Todd.
Remember, you only have to get this PERFECT once, and you're good for a LONG time. The consequences of not getting it perfect are really BAD! Todd.

*72lb4x4* · 12-05-2008, 04:18 AM

You might tr flushing the system and then bleeding it. Brake fluid absorbs air naturally and need to be flushed occasionally. Maybe especially in this case due to the er, sinking...

dana b · 12-05-2008, 12:01 PM

Wow- thanks!! My son & I will be trying this this weekend- I'll let ya know how it goes. He is anxious to get it on the road.

72lb4x4- ya a guy at our parts store told me the same thing yesterday. I have also learned that letting these things sit forever is not good at all- you should have saw how nasty the gas was we took out when we dropped the tank.

James McClure · 12-05-2008, 12:29 PM

Dana, brake hoses? badly rusted lines and another leak? A really dumb question, are the front calipers reversed left to right leaving the bleeders on the bottom? Don't laugh, I've seen it before and it's easy to do.

454HO · 12-05-2008, 01:05 PM

If all else fails, try this - Pressure Bleeder

Mr79C10 · 12-05-2008, 06:07 PM

Quote:

Originally Posted by 454HO

If all else fails, try this - Pressure Bleeder

Great idea, why didnt I think of that?

asphaltburner · 12-06-2008, 03:03 AM

Nice,...but that master cylinder cap is for very early single reservoir masters. For dual master cylinder reservoirs you'd need two fittings and a proper cap with gasket. And a half gallon of brake fluid to fill the sprayer? You'd be getting into some expense. Great for professionals, but how many brake systems are ya gonna bleed? For one time use, it wouldn't be cost effective. I just can't think of a cost-efficient alternative,...but I'm intrigued by the idea!
Perhaps pressurize an upside down brake fluid container,...
Todd.

12-03-2008, 01:05 PM	#1
dana b Registered User Join Date: Nov 2008 Location: IOWA Posts: 5	brakes Having brake headaches with this 81 GMC. Before we purchased this truck it had been immersed in water & then sat for 4-5 years. So we have had to replace a lot of stuff. We gave it a complete brake job- new everything & bled them really good & several times. Brakes are still mushy. Tried a few other things- someone suggested the splitter was sticking- changed it- still the same- we are thinking the booster maybe? Any suggestions appreciated.

12-03-2008, 09:33 PM	#2
asphaltburner Registered User Join Date: Jul 2008 Location: Ault, Colorado Posts: 862	Re: brakes Yo! Booster, or no booster, you should still get a good solid feel to the brake pedal if they've got a solid column of fliud. A bad booster will make a sucking noise when the brakes are applied with engine running. Did you bench-bleed the master if it was replaced? Did you bleed the brake lines "two person" or with a suction bleeder at each wheel? Sounds like you're still dealing with air in the fluid column. Will the brakes "pump up" as you repeatedly apply the pedal? Todd. __________________ '78 3/4 ton 4x4 custom "Todd-built" FRANKENTRUCK!

12-03-2008, 09:45 PM	#4
AceX >130dB Moderator Join Date: Aug 2006 Location: Sacramento, CA Posts: 2,130	Re: brakes Check the booster as well __________________ Living Life @ 130dB LED Tail Light Conversion; How-to Friend. Father. Brother. RIP El Jay ------------------------------------------------------------------------------------------------------------------------- CLICK HERE and for less than $0.07 a day, you too can help support and build a better forum.

12-03-2008, 10:17 PM	#5
asphaltburner Registered User Join Date: Jul 2008 Location: Ault, Colorado Posts: 862	Re: brakes Yo! AceX! How do you check your boosters? All I know is to listen for the leaking engine vacuum when the brake is applied, engine running. My '69 F100 has this problem. Is there a slick, easy check? Todd. __________________ '78 3/4 ton 4x4 custom "Todd-built" FRANKENTRUCK!

12-05-2008, 02:22 AM	#6
asphaltburner Registered User Join Date: Jul 2008 Location: Ault, Colorado Posts: 862	Re: brakes Yo! It's absolutely essential to clear ALL the air from the master cylinder on the bench, since it's so hard to do any other way. You can push the piston in with a punch or screwdriver, and put your fingers over the output holes to release the plunger. Repeat until you get no air at the outputs or inside the bowls. Messy,...although I've seen short pieces of brake line attached to the outputs and bent to return fluid into the bowls (the bent line ends need to be emmersed,...or plugged when the piston is released so they won't suck air)! And then I install the master (try to plug the outputs as you do so), keep it full, and begin bleeding the pass. rear first until there's no bubbles (even tiny ones). Then driver's rear, then pass. front, driver's front. It's good (with two people) to pump that pedal multiple times, place pressure on it, open the bleeder a bit, and then close the bleeder just before the pedal is all the way down. Takes some coordination, and repetition, but gives great results. If there's ANY pumpup after bleeding (I hate to say it, but), do it again. I have opened all the bleeders for a day or so before bleeding, and kept the master full, so that gravity could help fill the lines initially, then bled the brakes normally. All and all, the idea is for the master to suck fluid from each bowl, the pistons to push it through the lines to the bleeders, and never to allow air to suck back in when the pistons are released. Todd. Remember, you only have to get this PERFECT once, and you're good for a LONG time. The consequences of not getting it perfect are really BAD! Todd. __________________ '78 3/4 ton 4x4 custom "Todd-built" FRANKENTRUCK! Last edited by asphaltburner; 12-05-2008 at 02:23 AM.

12-05-2008, 04:18 AM	#7
72lb4x4 Account Suspended Join Date: Jul 2006 Location: DFW Posts: 1,427	Re: brakes You might tr flushing the system and then bleeding it. Brake fluid absorbs air naturally and need to be flushed occasionally. Maybe especially in this case due to the er, sinking...

12-05-2008, 12:01 PM	#8
dana b Registered User Join Date: Nov 2008 Location: IOWA Posts: 5	Re: brakes Wow- thanks!! My son & I will be trying this this weekend- I'll let ya know how it goes. He is anxious to get it on the road. 72lb4x4- ya a guy at our parts store told me the same thing yesterday. I have also learned that letting these things sit forever is not good at all- you should have saw how nasty the gas was we took out when we dropped the tank.

12-05-2008, 12:29 PM	#9
James McClure One shot, one kill. Join Date: Dec 2007 Location: Saratoga Springs NY Posts: 859	Re: brakes Dana, brake hoses? badly rusted lines and another leak? A really dumb question, are the front calipers reversed left to right leaving the bleeders on the bottom? Don't laugh, I've seen it before and it's easy to do. __________________ 1984 K20 350M engine with 465,000 miles. Well, it's finally done!! Almost 2 years of work, but it was really worth the effort. Little stuff left to do is mount winch, wet sand & buff out and build belly pan\running boards. Body work takes lots and LOTS of beer!!!! God, Guts and Guns made America and God, Guts and Guns will preserve it! The worst thing you could do is get into my sights, but that don't matter, you'll never know it, cause you'll never hear the shotJim or Paladin whichever you choose.

12-05-2008, 01:05 PM	#10
454HO Registered User Join Date: Apr 2005 Location: Austin, TX Posts: 1,224	Re: brakes If all else fails, try this - Pressure Bleeder __________________ - Greg

12-06-2008, 03:03 AM	#12
asphaltburner Registered User Join Date: Jul 2008 Location: Ault, Colorado Posts: 862	Re: brakes Nice,...but that master cylinder cap is for very early single reservoir masters. For dual master cylinder reservoirs you'd need two fittings and a proper cap with gasket. And a half gallon of brake fluid to fill the sprayer? You'd be getting into some expense. Great for professionals, but how many brake systems are ya gonna bleed? For one time use, it wouldn't be cost effective. I just can't think of a cost-efficient alternative,...but I'm intrigued by the idea! Perhaps pressurize an upside down brake fluid container,... Todd. __________________ '78 3/4 ton 4x4 custom "Todd-built" FRANKENTRUCK!



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.