Proportioning Vavle for Disc Brake Conversion on a 1970 GMC C-20

[SonomaComa]

I purchased a 1970 GMC C-20 that already had a Disc Brake Conversion. I was told that he used the Spindle and Calipers from a 1972 Chevy Truck. The Upper Ball Joint had to be changed too because the taper on it was different for the Spindle. It does not have Power Brakes. I was wondering about a Proportioning Valve.
There is some sort of Distribution Box that the Brake Lines from the Master Cylinder go into and then one line goes out to the Front Brakes and one goes to the Rear Brakes. There is also one more Brake Line that goes to an old fashioned Trailer Brake Controller, the kind with a slide handle inside the Cab.
Would it be best to just hook the brake lines up directly to the Master Cylinder and install an adjustable Wilwood Proportioning Valve on the Rear Brake Line just for the Rear Brakes and run the Fronts right out of the Master? http://www.wilwood.com/MasterCylinde...temno=260-8419
What is the purpose of that Distribution Box? Was that stock on a 1970 GMC C-20?

[Mmorgan32]

My truck had it. It's for the trailer brake controller. I took the junction box off( my trailer brakes didn't work) I left the controller on the inside. I like the way it looks. I just ordered a disc brake conversion. Hasn't come yet but from what I can tell and and what I remember of my 72 yes u run the lines from the master to the prop valve and then down to the front and back. The lines are different tho. I had to order a prop valve set of brake lines or u can make them

I think the trailer brakes were a dealer add on. Mines a camper and the gas tanks and everything were a dealer add on

[swamp rat]

You can get the proper distribution/proportioning valve from Inline tube, call them and let them know what you have. Or possibly order one for a 72 chevy truck from an auto parts store.

[SonomaComa]

So You don't think the Adjustable Proportioning Valve is a good idea?
http://www.wilwood.com/MasterCylinde...temno=260-8419

[Mmorgan32]

I wouldn't put an adjustable one on. My brother has one down on his frame rails of his camaro and he can't get it adjusted right. If u were racing your truck then I'd say go for it. I'm putting a stock one on my truck. It's all done for you

[72MARIO]

I have adjustable valves in my suburban and 1967 C20. No problem getting it adjusted.

[67chevemall]

I have a few of the cpp inline psi controls if you want to go that route.
2 on the front 2 on the back.
10 lbs on the fronts and 2 lbs on the back

I used a adj. port. valve and it was set perfect right out the box.

[SonomaComa]

Originally Posted by 67chevemall

I have a few of the cpp inline psi controls if you want to go that route.
2 on the front 2 on the back.
10 lbs on the fronts and 2 lbs on the back

I used a adj. port. valve and it was set perfect right out the box.

Wow those are neat. I thought I wasn't supposed to restrict the Front Brakes,
only adjust the Rear to the Fronts. But how does yours work, are they adjustable or pre set?

[67chevemall]

I use the adjustable one.

The preset ones I was going to hide in the frame rail but chose not to use them
Free plus shipping if you want to try them

[SonomaComa]

Originally Posted by 72MARIO

I have adjustable valves in my suburban and 1967 C20. No problem getting it adjusted.

How did you adjust yours? Did you just drive and adjust it until it felt good? Or did you adjust it with by pressure testing it?
What should the pressure be at the Front Calipers and Rear Wheel Cylinders?

[Ruscal]

I find it easiest to adjust the brake bias on a dirt road with winding turns due to less traction. If you brake going into a turn the rear end will hang out early if you have too much rear brake. Back off the rear bias until the truck holds its line when braking into the corner and you're good to go. Dry asphalt paving can hide minor bias problems that would cause problems when wet. Dirt roads simulate wet pavement.
Russ

[67chevemall]

Stomp on the brakes and see what happens...should slide straight

[Ruscal]

Originally Posted by SonomaComa

Wow those are neat. I thought I wasn't supposed to restrict the Front Brakes,
only adjust the Rear to the Fronts. But how does yours work, are they adjustable or pre set?

I think those inline valves are needed when your master cylinder is mounted below the floor. (Low) It keeps a small amount of residual pressure against the wheel cylinders or calipers.
Russ

[SonomaComa]

Originally Posted by Ruscal

I find it easiest to adjust the brake bias on a dirt road with winding turns due to less traction. If you brake going into a turn the rear end will hang out early if you have too much rear brake. Back off the rear bias until the truck holds its line when braking into the corner and you're good to go. Dry asphalt paving can hide minor bias problems that would cause problems when wet. Dirt roads simulate wet pavement.
Russ

That is an awesome idea!

[davepl]

I have a factory 1970 unit kicking around from my drum brake C2500 if you get desperate. It's the nonadjustable unit but 1,000,000 factory trucks can't be wrong!

[davepl]

Originally Posted by 67chevemall

Stomp on the brakes and see what happens...should slide straight

Actually that's not the point - even if it was way out of adjustment if you lock up all four, you're past the point of this anyway.

It's when the rears lock up during threshold braking; if they lock up too early, you'll bring the rear end around. Too late, they're not doing their share of the work.