04-10-2024, 11:46 PM | #1 |
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Join Date: Dec 2009
Location: Sask. Canada
Posts: 5
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Hydroboost on 81
Been a while since I checked in here but I'm having brake problems and looking for ideas. The original hydroboost brake system has worked great from day one on my 81 Sierra Classic pickup but recently I'm getting only front brakes applying and takes more pedal pressure to stop. Rear wheel up on blocks test shows the rear brakes will apply on a quick pedal push but gradual pedal application gives almost no braking and the pedal goes down more as if pressure is by passing somewhere yet there are no visible leaks. Brake fluid is old and dark. Maybe the master cylinder is weak? The truck is a former diesel but now gas and have run with the original diesel steering pump and brakes since the swap in 86.
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04-11-2024, 06:58 AM | #2 |
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Join Date: May 2015
Location: Alabama
Posts: 14,670
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Re: Hydroboost on 81
The hydroboost has no effect on which wheels stop when mashing the pedal... sounds like maybe your master is bad...have you tried bleeding rear brakes? Also on the proportioning valve, it has the trip feature, meaning the internal spool can trip and send all the fluid to front or back....check and make sure it isn't tripped..mine was one time and all I had was rear brakes.. they make a tool to screw into it to hold the spool centered so you can bleed the system..
Another thing to check is the condition of the rubber hoses, If they're orig,it's probably best to put new ones on, At the least it sounds like your system needs flushed..
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Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver |
04-11-2024, 12:14 PM | #3 |
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Location: Oklahoma City, OK
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Re: Hydroboost on 81
2nd on the MC. Also replacing the hoses if original. If you replace the hoses, might as well replace the rear wheel cylinders. Inspect the fronts and replace if worn. Get dirty once, have a fresh brake system.
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04-12-2024, 09:47 AM | #4 | |
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Re: Hydroboost on 81
Quote:
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04-12-2024, 11:55 PM | #5 |
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Join Date: May 2015
Location: Alabama
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Re: Hydroboost on 81
some prop valves you can reset by a button on the end of it...my 81 had that button..mashing it recentered the spool..
to adj brakes get them close manually with the adj, then button everything up..start backing up and mashing ebrake..do this several times and itll adj the shoes
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Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver |
04-13-2024, 09:38 AM | #6 | |
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Re: Hydroboost on 81
Quote:
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04-13-2024, 01:59 PM | #7 |
Post Whore
Join Date: May 2015
Location: Alabama
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Re: Hydroboost on 81
"My parking brake is non operational due to a damaged cable"
That's why you can't adj the rear shoes then
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Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver |
04-20-2024, 09:37 PM | #8 |
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Join Date: Dec 2009
Location: Sask. Canada
Posts: 5
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Re: Hydroboost on 81
No, the parking brake has nothing to do with the self adjusting feature. This from a veteran heavy duty mechanic and a GM partsman. It turned out to be the master cylinder. New cylinder installed and its back to normal four wheel braking.
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