Proportioning valve

[63longfleet]

The continued saga of the front disc upgrade. I had already split my brake lines and upgraded to a duel master for drum/drum. I know I need to swap that out for a drum/disc do I need the big proportioning valve or can I just use one of the small online ones for the back brakes? Thanks in advance
Charles

[Indian113]

I don't think you will need a Valve on Drum/Drum only on Disc/Drum. I am sorry I misread your post. In The FAQ section is a complete list of work and or parts needed to rebuild and replace Brakes.

[The Rocknrod]

Here are the discussion on disc brakes: http://67-72chevytrucks.com/vboard/s...15&postcount=2

[63longfleet]

Ok after 2 str8 hrs of reading the FAQ section i still cant find an answer to this question. Lots of reference to using the "big" prop valve when originally doing the disc swap and the line split at the same time. But none about my situation regarding using a inline adjustable prop valve on the line for the back brakes and not cutting into the front system to install the bigger stock style valve.

[The Rocknrod]

If you do install a rear brake proportioning valve you'll have to conduct a few panic stops to ensure the rear brakes don't lock up first.
I installed one like this on few of my builds and did the brake check and adjusting.
http://www.superchevy.com/how-to/713...tioning-valve/

[Short 3/4]

Originally Posted by The Rocknrod

If you do install a rear brake proportioning valve you'll have to conduct a few panic stops to ensure the rear brakes don't lock up first.
I installed one like this on few of my builds and did the brake check and adjusting.
http://www.superchevy.com/how-to/713...tioning-valve/

I also used one like this. Very important to use a master cyl that is for a disc/drum application. on my old 66 it bolted right in, though I recall I may have had to shorten the activating rod from the pedal.
Now just plumb in the adjustable prop valve to the rear brake line ( careful that you go to correct port, there is a front and rear)
To adjust, I found it best to find a hard packed gravel road (with no traffic) and adjust so the fronts lock up very slightly before the rears. If you carry a load or pull a trailer, make sure truck is loaded for test, or test both loaded and unloaded and mark position of dial for each
I like test on gravel because you don't ware out your tires trying to lock them up on pavement
Did this on my old 66 and worked very well for many years, especially when loaded (it was a work truck)
Good luck, Tom

[geezer#99]

X2.
I used one like that but plumbed in a 2# residual check valve for the front and a 10# one for the back.
The prop valve acts as a check valve when you use one. Keeps fluid from draining back.

[Chevy Fleetside]

Can it hurt to try and I don't see why it wouldn't work. Your just limiting the pressure to the rear brakes.

[nsb29]

I might be wrong But my understanding of what you’re calling that big proportioning valve is not It is a switch to turn your brake Light on the dash If you have a failure that caused aloss of fluid to the front or rear brakes it also let the pressure to the rear brakes first so you stop strait yet does not regulate the amount of pressure between front and rear Master cylinder does that in different bore size

[SkinnyG]

The big valve is likely a "Combination Valve" (sourced from later trucks, right?). It is a "combination" of:

1) Pressure Differential Valve: "Seals off" the failed half of the brake system if there is a leak so you still have half your brakes. This will also trigger the "BRAKE" light on the dash telling you that you have a problem.

2) Proportioning Valve: "Limits" maximum rear brake pressure so that under heavy braking and the rear of the truck is unloaded, the brakes don't lock and you swap ends.

3) Metering Valve: Allows pressure to begin to the rear brakes first, because they have to overcome spring pressure, whereas the disc are right there ready to go. Theoretically the disc and drum brakes will then -begin- braking at the same time.

[nsb29]

Originally Posted by SkinnyG

The big valve is likely a "Combination Valve" (sourced from later trucks, right?). It is a "combination" of:

1) Pressure Differential Valve: "Seals off" the failed half of the brake system if there is a leak so you still have half your brakes. This will also trigger the "BRAKE" light on the dash telling you that you have a problem.

2) Proportioning Valve: "Limits" maximum rear brake pressure so that under heavy braking and the rear of the truck is unloaded, the brakes don't lock and you swap ends.

3) Metering Valve: Allows pressure to begin to the rear brakes first, because they have to overcome spring pressure, whereas the disc are right there ready to go. Theoretically the disc and drum brakes will then -begin- braking at the same time.

You are correct a much better explanation than what I gave years ago I had the privilege of meeting Smoky yunek I know I spelled his last name wrong but anyway before they made proportioning valve if they had too much rear break they would removed part of the brake shoe for less rear brake