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Old 06-23-2018, 04:08 PM   #1
6cylinderstepside
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Any reason a Brake Proportinoing Valve is not available?

I am working on my brakes after the 79 has been sitting for a a couple years and the master cylinder is a bit leaky and the left front caliper is dragging. I have manual brakes and they are factory disc in front. the rears are fine. I decided to just replace it all in the front so I swapped out the MC and both calipers and the brakes are still dragging on the drivers side but release when I open the bleeder. Now it seems the culprit is the proportioning valve. The hose doesn't make sense as being the problem as it gets pressure and then releases with opening the bleeder. I checked the button on the valve but it's not popped up and the brake light is not on. I just replaced the tranny and did alot of work to the truck getting it ready for prime time, even the interior and it is ready to roll and this last thing is the only thing stopping me!

So that is where I am... I am about to try the ole open the bleeder on the good side and pump the brakes to center the proportioning valve again (hopefully) to free up the caliper but in the meantime I was checking auto parts store for a replacement and the usual suspects don't even show a proportioning valve listed to order more less in stock. If I clear the truck, parts show up, but when I add a vehicle it act like the truck doesn't even come with one but I am sitting here looking at it. Anyone ever heard of that or have anything else to try?

What gives with that?
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Old 06-23-2018, 04:28 PM   #2
cadillac_al
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Re: Any reason a Brake Proportinoing Valve is not available?

It sounds like the brake hose isn't letting the pressure release. I think you need a new brake hose on the offending caliper. Speedway Motors should have prop valves if you need one.
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Old 06-23-2018, 04:50 PM   #3
dmack91
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Re: Any reason a Brake Proportinoing Valve is not available?

I agree with Al. The inner hose will separate and leak pressurized fluid between the inner and outer layer, causing the line to effectively pinch off the opening and hold pressure at the caliper.
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Old 06-23-2018, 05:04 PM   #4
6cylinderstepside
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Re: Any reason a Brake Proportinoing Valve is not available?

Hell, I'll buy that... Two hoses coming right up... Get me on the damn road! Thanks guys, I'll post when done.
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Old 06-24-2018, 11:28 AM   #5
hatzie
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Re: Any reason a Brake Proportinoing Valve is not available?

I always replace the hoses when I swap calipers. Not worth the headache instantly or down the line when they collapse inside.

It's not just a proportioning valve... It's a Metering, pressure differential, and proportioning valve. The proper name for it is a combination valve. There were very few GM rigs after 1970 or so til the introduction of ABS that had separate valves.

Combination valves are engineered for your vehicle weight distribution brake type etc. The 79-84 parts books list two valves depending on GVW. The 85-91 parts books have several pages of different combination valves depending on year, GVW, Brake system RPO, etc. I didn't bother to search the 73-78 books. It's unlikely there's just one combination valve for that year range.

I always rebuild the original rather than installing a Chinese one-size-fits-all valve that's wrong for most applications. Usually, it's just dodgy o-rings and crud.
You can usually rebuild them fairly easily with new o-rings. They clean up with WD-40 and a toothbrush. Lube the internals with fresh brake fluid.
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And please let us know if and how your repairs were successful.
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Old 06-24-2018, 12:20 PM   #6
74CustomK20
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Re: Any reason a Brake Proportinoing Valve is not available?

I had a similar problem on my 98. Wound up being the master cylinder/booster combo.
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Old 06-25-2018, 05:56 PM   #7
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Re: Any reason a Brake Proportinoing Valve is not available?

Inlines Tubes.com makes nice ones. You just have make sure you order the same wire connection as you have. There made of brass or brass polished to look like chrome.
I think only after market now a days Inlines Tubes or as said.
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Old 06-25-2018, 09:54 PM   #8
87 STEPPER
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Wink Re: Any reason a Brake Proportinoing Valve is not available?

I think it may be your hose's but if not here's a link for a PV. Good luck.

https://www.carolinaclassictrucks.co...rop-Valve.html

BTW Nice truck love the baby moon's.
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