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#1 |
Suburban Hick
![]() Join Date: Aug 2008
Location: Altoona, IA
Posts: 810
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85 C3500 brake issues
So heres the scoop. I was drivingmy 85 crew cab last week and noticed the brake pedal fading more and more. I checked the reservoir and the front compartment was empty and the rear was full. There has to be a leak somewhere so I checked all the lines from front to back and they were all dry. I replaced the right side line that runs along the rear axle anyways as I did the left side a couple months ago. Filled the reservoir and bled the brakes. The first pumpgoes clear to the floor, bit will pump up on the 2nd and 3rd pump. We bled the brakes for 30 minutes and nothing changed. We were bleeding the brakes at the lines because the bleeders were rusted stuck. I decided to change out the wheel cylinders so I could bleed the brakes appropriately. Did that and after bleeding for quite awhile still the same results. Next decided to change the master cylinder. Bench bled that and bled the brakes again. So basically everything has been replaced and I cannot find any leaks anywhere. So when you go to stop the pedal at first has a little bit of pressure and you feel the brakes grab right away and then let go and you can continue topush the pedal down clear to the floor before they grab again. Yet you can pump them a couple times and then they're like normal. I should add that this truck has hydraboost. Anybody have any ideas?
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Mathew 1947 Chevy 3600 1951 GMC 100 1969 Chevy C-10 396/500hp TH400 lowered 4" 1968 Imapla Custom 396/325hp TH400 "Grandmas Car" 1976 Crew Cab 4x4 diesel http://67-72chevytrucks.com/vboard/s...d.php?t=488505 1978 Chevy K-10 454 1983 S10 4x4 "Bumblb" (Grandpa's truck) 1993 Chevy S10 V8 conversion 1990 Ford Probe Gt 1992 Dodge W-150 "Old Man's Truck" 1992 Pontiac Grand Prix SE 1992 Mercury Grand Marquis-Mercruiser 2000 Ford F150 (Currently my mother drives this) 1946 Farmall H with Stan Hoist loader 1965 John Deere 110 1961 Wheel Horse " Rat Tractor" |
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#2 |
Registered User
Join Date: Dec 2006
Location: North Carolina
Posts: 308
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Re: 85 C3500 brake issues
I have had my 85 for years and always has issues with my brakes and could never get them to bleed correctly so I set pans under each bleeder port and let gravity bleed for 30 min while topping off fluid and worked for me. I also recently replaced master cylinder and front calibers and now they bleed great.
Are you still losing fluid after your replacements?
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#3 |
Suburban Hick
![]() Join Date: Aug 2008
Location: Altoona, IA
Posts: 810
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Re: 85 C3500 brake issues
I haven't drove it enough to find out. The last loss was over a 3 month period. That was the last time I checked it anyway.with the engine running, I can pump the brakes up and hold them for a couple minutes and the pedal won't go down at all. I'm just baffled with this.
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Mathew 1947 Chevy 3600 1951 GMC 100 1969 Chevy C-10 396/500hp TH400 lowered 4" 1968 Imapla Custom 396/325hp TH400 "Grandmas Car" 1976 Crew Cab 4x4 diesel http://67-72chevytrucks.com/vboard/s...d.php?t=488505 1978 Chevy K-10 454 1983 S10 4x4 "Bumblb" (Grandpa's truck) 1993 Chevy S10 V8 conversion 1990 Ford Probe Gt 1992 Dodge W-150 "Old Man's Truck" 1992 Pontiac Grand Prix SE 1992 Mercury Grand Marquis-Mercruiser 2000 Ford F150 (Currently my mother drives this) 1946 Farmall H with Stan Hoist loader 1965 John Deere 110 1961 Wheel Horse " Rat Tractor" |
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#4 |
Suburban Hick
![]() Join Date: Aug 2008
Location: Altoona, IA
Posts: 810
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Re: 85 C3500 brake issues
I should also mention that it has, what I call it anyway, a manually adjustable proportioning valve on the rear axle. It bolts to the frame and has an arm that attaches to the axle itself. I read it works based on the amount of weight on the truck so basically ride height. Could this be bad and causing my issues?
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Mathew 1947 Chevy 3600 1951 GMC 100 1969 Chevy C-10 396/500hp TH400 lowered 4" 1968 Imapla Custom 396/325hp TH400 "Grandmas Car" 1976 Crew Cab 4x4 diesel http://67-72chevytrucks.com/vboard/s...d.php?t=488505 1978 Chevy K-10 454 1983 S10 4x4 "Bumblb" (Grandpa's truck) 1993 Chevy S10 V8 conversion 1990 Ford Probe Gt 1992 Dodge W-150 "Old Man's Truck" 1992 Pontiac Grand Prix SE 1992 Mercury Grand Marquis-Mercruiser 2000 Ford F150 (Currently my mother drives this) 1946 Farmall H with Stan Hoist loader 1965 John Deere 110 1961 Wheel Horse " Rat Tractor" |
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#5 |
Registered User
Join Date: Sep 2009
Location: Beaverton, OR from WA State
Posts: 1,515
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Re: 85 C3500 brake issues
I think if that rear load-dependent valve fails it would just restrict the flow (or not at all depending on where it failed) and cause you to brake unevenly front to rear.
Here is a recent thread about it. In this thread it is mentioned WHY GM added it, what their intentions were, and the service bulletin that THEY published to remove it. ![]()
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Devin 1983 GMC High Sierra 2500, 4x4, RC/LB, 400 S.B., SM-465, NP-208, Corporate 10 bolt & 9.5" 14 bolt 1996 GMC Sierra SLE 3500 DRW, 4x4, EC/LB, Vortec 454, NV-4500, BW-4401, AAM 925 & AAM 1050 1997 GMC Sierra SLT 1500 4x4, Z71/F44, EC/SB, Vortec 350 My Introduction with my '83s History New Daily, the '96 |
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#6 |
Suburban Hick
![]() Join Date: Aug 2008
Location: Altoona, IA
Posts: 810
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Re: 85 C3500 brake issues
I think I'll try removing that this weekend, just to eliminate one more variable and see what happens.
__________________
Mathew 1947 Chevy 3600 1951 GMC 100 1969 Chevy C-10 396/500hp TH400 lowered 4" 1968 Imapla Custom 396/325hp TH400 "Grandmas Car" 1976 Crew Cab 4x4 diesel http://67-72chevytrucks.com/vboard/s...d.php?t=488505 1978 Chevy K-10 454 1983 S10 4x4 "Bumblb" (Grandpa's truck) 1993 Chevy S10 V8 conversion 1990 Ford Probe Gt 1992 Dodge W-150 "Old Man's Truck" 1992 Pontiac Grand Prix SE 1992 Mercury Grand Marquis-Mercruiser 2000 Ford F150 (Currently my mother drives this) 1946 Farmall H with Stan Hoist loader 1965 John Deere 110 1961 Wheel Horse " Rat Tractor" |
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