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what proportioning valve for rear disc swap on 86 chevy?

6K views 8 replies 4 participants last post by  abig84 
#1 ·
1986 k30, put the 1/2 ton dana 44 calipers and rotors in the back about a year agok anyways the brakes have always been spongy but the truck does stop good on dry roads. a few days ago we had ice i slammed on the brakes and the rears didnt lock up. even tried bleeding it again and go no air.

i remember reading something about some cadi proportioning valve that you are supposed to use, id like to give that a try and see if thatll fix it. anyone know the part number. i tried searching but didnt come up.
 
#2 ·
dont know

about the part # for the caddi proportioning valve, but couldnt you just buy an adjustable one and dial it in till your happy with them.

Also dont disc take less fluid but slightly higher constant line pressure (2-3psi vs 10-12psi iirc) to work properly than drums. I know in hotrod catalogs they sell different residaul (sp?) valves that go inline depending on disc vs drums
 
#3 ·
When I did my disc swap, I just used a adjustable proportioning valve from summit, you can adjust it how you like it.

FredyC you got it backwards. Discs take more fluid (look at the size of the caliper bore vs a tiny wheel cylinder in drum brakes). You don't need a residual pressure valve unless your MC is mounted low, like under the floor in hot rods.
 
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#5 ·
$6 and i will front you on it, if it dont works fuck it.
appreciate the offer :smokin: im just gonna go with a new one. this stupid thing did work fine on this truck and my prior truck before doing the rear disc swap, id rather just buy something new and be done with it. looks like ill just get the summit one. thanks
 
#4 ·
Sounds like the shuttle part of the combo valve may be shuttled. The pin at the plug would be at ground (or the brake warning light would be on if you have one)

Usually you can jam on the brake pedal sharply and it should unseat. Sometimes you have to open a bleeder and do it. Then rebleed slowly.

It is ok to remove the residual pressure valve for rear discs. Usually behind the adaptor fitting for the rears.
 
#6 ·
so i bought a adjustable proportioning valve. not quite sure if i got the right one. basically it goes in just one of the lines. i figured it would do all 4 like a factory one, it says in the directions to not put in between the master cylinder and the proportioning valve. so where the hell am i supposed to put it. if i put it after id have to buy one for each side of the front. the back is the one getting no pressure so putting it in the back line isnt gonna do anything. im confused.
 
#7 ·
You'll have to do a little brake line plumbing. Remove the stock prop valve, tee the front lines, the adjustable prop valve goes in the rear line. Front lines get full line pressure, then you can dial in the rear bias by adjusting the adjustable prop valve.
 
#9 ·
just a update encase any searches. i did buy the proportioning valve but never got around to putting it on. i ended up buying a master cylinder for a 1999 c3500. bolts right up to my 86 chevy, even the lines were the exact. truck stops better then a brand new truck. all 4 tires even locked up when i slammed on it with 33 inch tires.
 
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