Adjustable Proportioning Valve - Required for Disc/Drum Setup??

[Rack Man]

I'm plumbing the brake lines for my 70 K-10 project....I swapped the front axle to a mid 70's Dana 44 w/Disc Brakes (rears are still drum).....I ordered all new SS lines from Inline tube (which 50% are too short)....They also sent me an adjustable proportioning valve...Is this valve necessary even with the regular proportioning valve located at the master cylinder?....or is it meant for fine tuning the rear drums in more of a performance application?

Thanks in advance for any insight you can give me!

Dan

[vin63]

Is the proportioning valve near the master cylinder for the front disc/rear drum bias?

[Rack Man]

I have nothing right now...so I guess it could be.....But I'm clueless.....I am in the middle off a frame off resto....so I still need to purchase the MC, power booster & proportioning valve......Just trying to get the main brake lines ran while i'm at the frame level.....

Originally Posted by vin63

Is the proportioning valve near the master cylinder for the front disc/rear drum bias?

[vin63]

Gotcha...many of the master cylinder (MC) kits come with an OE-type proportioning valve assembly pre-plumbed mounted at the MC, and you can specify disc/drum or disc/disc bias. The adjustable proportioning valve is often used inline on the tubing going to rear brakes when you do not have a factory-type proportioning valve at the master cylinder. I run the adjustable type on my rear brakes of my drag car just to make sure there is more braking being done by my front brakes.

[Painter D]

I don't know for sure if it's absolutely necessary to have it, but I had to have the adjustable one, along with the regular one. Before the adjustable one was installed my back brakes would lock up when I hit the brake pedal.

[leftcoast66]

Not sure with the regular one involved, but without it yes it is necessary. It takes I believe 10lbs of pressure to make drum brake works and I believe it was 2lbs of pressure to make disc's work. So put it on the disc side to limit it so that they aren't biased towards the fronts locking up.

[LONGHAIR]

Originally Posted by leftcoast66

Not sure with the regular one involved, but without it yes it is necessary. It takes I believe 10lbs of pressure to make drum brake works and I believe it was 2lbs of pressure to make disc's work. So put it on the disc side to limit it so that they aren't biased towards the fronts locking up.

leftcoast66, he is referring to an adjustable proportioning valve. What you are talking about is called a "residual valve". Residual valves maintain pressure on the lines to keep them ready instantly.
An adjustable proportioning valve gives you the ability to restrict pressure to one end, to equalize the actual braking. It is usually the back that has a tendency to lock-up, especially when the bed is empty.

[vin63]

Originally Posted by leftcoast66

Not sure with the regular one involved, but without it yes it is necessary. It takes I believe 10lbs of pressure to make drum brake works and I believe it was 2lbs of pressure to make disc's work. So put it on the disc side to limit it so that they aren't biased towards the fronts locking up.

Hmmm...I'm not sure I would reduce any braking to the front brakes with an adjustable proportioning valve. Our trucks are pretty light in the back compared to the front to begin with. The last thing I would want is the back end of my truck wanting to swap ends with the front every time I had to brake hard. If you're talking about a residual valve, if he locates the master cylinder up on the firewall, he won't need them. I run residual pressure valves on my race car, but that's because my master cylinder is located under the floor below the level of the calipers.

[ENHANCED AIR RIDE]

The standard prop valve is what you will need to run your disc/drum setup. it can mount near master or down on frame, it does not matter. We have them in brass and SS.