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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: bigred on August 12, 2006, 06:06:00 pm

Title: Brake help
Post by: bigred on August 12, 2006, 06:06:00 pm

My 85 had a leaky brake wheel cylinder so my dad and I put a new one on it. The problem is we can't get any pressure to the rear brakes. We tried holding in on the button on the proportioning valve (located on the left side of the front of the frame) but we still can't get pressure back there. I'm guessing the valve is messed up or has something in it or something.  The rear brakes had been sliding easier than they should and they weren't too tight. I know fluid can make them grab but I think maybe the valve was acting up. Does this sound like the problem? Where can u get the proportion valve? Is this a  dealer item? I call some auto parts and they don't have it. I saw it in   for $100.

Title: Re: Brake help
Post by: 79apache on August 12, 2006, 06:22:00 pm

Double check and make sure you have the right part number for the wheel cyl. for your size of brakes. There is more than one size.
You might try the autozone autoparts website for a look-see.

Last time I did this I had the same problem and wrong part was the cause.

Good luck!

Edited by: 79apache at: 8/12/06 5:30 pm

Title: Re: Brake help
Post by: Lt.Del on August 12, 2006, 08:16:00 pm

You can see if you are getting hydraulic pressure by loosening the brake  line at the wheel cylinder.  have someone push down on brake pedal and see if fluid squirts out...sort of like bleeding the line but by loosening the line and not the bleeder screw.

If you need a new p valve, i'd get a used one from a salvage yard.

SgtDel
aka "Andy"

www.delbridge.net

1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4

Edited by: SgtDel  at: 8/12/06 7:17 pm

Title: Re: Brake help
Post by: bigred on August 13, 2006, 12:46:00 am

Thanks. There was no pressure on the line either. I even tried it directly on the rear side at the  p valve. I guess I look for a used one.

Title: Re: Brake help
Post by: WickedC20 on August 13, 2006, 07:34:00 am

Ive ran into this before...I have no explanation as to why this happens,but this only happens on GM trucks...weird
Normally when this happens, one wheel will have good pressure and the other has none, or when the fluid comes out, it comes out fast for 1/2 a sec then it slowly comes out sooooo
#1. Grab a friend or your dad, Open the RR wheel cylinder bleeder valve, then have whoever can help mash on the pedal with some force. Watch how much and how fast the fluid squirts out.
Do the same for the LR wheel. Just to see if this is happening.
If so, crack the lines loose at the Proportining Valve and let them drip for a few minutes, then bleed the sending lines off of that Prop Valve. You may want to try this over and over, sometimes getting trapped air out of a system is such a pain...
(yesterday...on an Isuzu, It took me over 3 hours to bleed a clutch line)
If you still have this problem.... crack open the Master Cylinder lines, leave the top off and let the MC drip for a few hours,(ive had to wait over 6 hrs before...so be patient) eyeball the fluid level so the MC doesnt go dry.
Then repeat the 1st step
Ive tried replacing the MC before because of this problem, It was no better.

Title: Re: Brake help
Post by: VileZambonie on August 13, 2006, 07:42:00 pm

Did you bench bleed the master cylinder before you installed it?

Title: Re: Brake help
Post by: WickedC20 on August 14, 2006, 06:26:00 am

Honestly, I do a lazy bleed, I fill the resivoir only 1/4 full, I move the piston a couple times so I know its working, then I bleed the Master once the lines are hooked up.
I know I know... you gotta bench bleed!!!     I get the same results with each Master Cylinder I put on...

As a matter of fact, When I was working on the same truck I ordered a Master, lazy bled it, and I still had no fluid passing threw the rear wheel, I re-ordered another MC, this time I bench bleed this one, only to cure my curiostiy and still had the same results...no fluid to the same rear wheel.