I need a BRAKE...

Ok guys gimme some direction here. I have a 60's Chevy PU with disc brakes at all 4 corners. They were on it when I got it but no master cylinder or prop valve. It seems to be a myriad of oem parts and some fancy brackets. At any rate, I need them to work, so heres the question....I am going to run a Corvette master cylinder (NON power assist), do I need to invest in the little adjustable proportioning valve for the rear OR will it work just fine with a oem type prop. valve designed for 4 wheel disc brakes? Is there a difference in a proportioning valve for DUAL piston calipers as opposed to SINGLE?

 

i am definately no expert, but what little i do know says that the calipers have to be matched to the master and to each other....if the cylinder in the caliper is too large, the master wont move enough fluid to actuate them, and if the calipers are different sizes from each other, then the one(s) with the smallest cylinder(s) will do all the work...rendering the others useless...just a heads up.

 

I'd say run the adjustable prop valve. I have one on the Mustang and it works great.

The Vette mc will provide more than enough volume, but the stock prop valve may not be set correctly for your truck's weight and the brakes that are on it. With the adjustable valve you can set the rears to lock up the same time as the fronts.

 

I was pondering if I could get away with using a prop. valve off something like the Vette or a Trans Am with 4 wheel disc. Im going to have to have a prop. valve for the front anyway and was just wanting to simplify things as much as possible without having to buy something else to put in line....I may be OVER simplifying them!

 

I think it would either take a lot of math or a lot of trial and error to figure out the "fixed" valve you would want, and highly recommend an adjustable one.

I'm definitely no brake expert, but I can imagine all the things that to into the equation: weight, piston size, master cyl pressure, tire diameters, tread widths, rotor sizes and such.

Why are you leaning hard toward the fixed one?

 

U, my friend, are absolutely correct. All the factors are exactly whats driving me crazy! the only real reason that I wanted to find an oem fixed one that would work is because I'm already going to have to purchase one for the fronts anyway, so it'd just be nice to get one that worked front and rear and be done with it.

All the street rod and tri-five parts houses sell prop valves advertised for 4 wheel disc but when you call them with these questions they scratch their heads and say "just have to try it and see."

 

Figure out what you have for calipers,specifically Piston diameters.

Go from there.

 

I asked the same thing a few mouths ago and was told all i needed was two 2 psi rpv vavles for four wheel disc one for the front one for the rear

 

the 2# residual check valves are used when the master cylinder is under the floor to prevent fluid from draining back in. An adjustable prop valve is a good idea to balance out front/rear brakes so the fronts come on just before the rears. Like jonny o said, there are too many variables trying to get a late model prop valve to match your truck.
From Wilwood's site:
"This adjustment lets you fine tune the front to rear braking balance by proportionately decreasing the rear (or in some cases the front) brake line pressure."

 

I don't see why you need both one for the front and a separate one for the rear. Unless you have a really radical system with a ton of pressure, I thought one adjustable works for both front and back. I think all it does is adjusts the rear pressure versus the front's 100%.

 

Bingo, we have a winner....

 

Im thinking a stock valve for a truck with front disc and an adjustable valve from speedway for the rears. It looks like the adjustable is going to be the easy answer.

 

first you absolute need to know the piston diameter.
A 3 inch caliper piston and a 1/2 inch MC piston as a extream example wont work.
4 calipers with a 2 inch piston is 638 sq mm ( sorry I'm a metrich guy)
a dual 1 inch MC is 159 sq mm.
so for the caliper piston to move 1 mm the MC needs to move 4 mm.
If the MC piston is to large a LOT of presure on the pedal is needed .

Remco

 

Zman, johnny O, so is what I have been ASSuming is a residual valve for the front actually nothing more than a tee to seperate the lines?

 

That would be called a Tee.

 

Ignore that last question. I was mentally picturing a drum brake system for some reason. (I gotta lay off the sugar)

 

Let me ask the guy who i trust on this kind of stuff. I'm pretty sure you need 1 adjustment valve only. Again, just talking out my ass.