Prop / Combo Valve Interchange?

Mac · November 10, 2009, 11:13:34 AM

OK, So, I'm upgrading to front disc brakes on my `63 C-10 Chevy. I'm keeping the OE rear drum brakes. I bought a kit with rotors, calipers, etc. and I'm using a manual M/C from a `77 C-10.
Now I'm hunting a prop valve and I'm wondering if someone can tell me (or point me to the data) what all makes, models, years interchange.

Charlie Chops 1940 · November 10, 2009, 11:29:33 AM

Should be able to plumb one from the same truck series that you got the M/C from. They're all disc/drum starting sometime in the early 70's. If you get one from a yard, take the lines between the distribution block and the M/C.

Charlie

Mac · November 10, 2009, 03:12:30 PM

Quote from: "Charlie Chops 1940"Should be able to plumb one from the same truck series that you got the M/C from. They're all disc/drum starting sometime in the early 70's. If you get one from a yard, take the lines between the distribution block and the M/C.

Charlie

So, they use a dist. block, too? I know in a lot of cases the prop valve distributes. I guess that would be called a combo. valve?

And would it be different valves for manual and power brake?

Charlie Chops 1940 · November 10, 2009, 07:59:03 PM

Yes, I guess that is probably the correct term. I would stick with the pickup unit because the later truck probably is real close to the same weight distribution.

Charlie

enjenjo · November 10, 2009, 08:25:18 PM

Lets try to clear the valves up a bit.

Most cars and trucks use a combo valve in the brakes, it controls several functions.

The first is as a hold off valve. Since the rear brakes are kept tight to the drum, they don't have to move much to apply. On the other hand disc brakes at the front are pushed back from the rotor by flex in the parts, and in some cases the seal pulls them back a bit. So the hold off valve keeps the rear brakes from applying until the front brakes are applied. It makes it stop straighter, and keeps the rear tires from locking up.

The second is as a failsafe shut off valve, which comes in to play if one end or the other has a failure in the hydraulic system. This will shut off the fluid to the end that fails, reserving it for the end that still works. This part of the valve also contains a switch that will turn on a brake warning light on the dash in case of failure.

The third part is a so called "proportioning valve" which actually only controls, by delaying the pressure rise to the rear brakes. The longer the pedal is held, the more pressure the rear brakes will see until it is equal to the front.

Add on proportioning valves work in much the same way, but in some cases will close off the rear brake lines at a certain pressure, some predetermined, some adjustable.

The OE seldom include a true proportioning valve in the brakes for two reasons. Expense, and they can adjust the brake bias with wheel cylinder/caliper sizes.

So as Charlie pointed out if the brake sizes are comparable to the truck you take the master cylinder and disc brakes from, a proportioning vale will not be needed. Manual or Power boosted makes no difference in the valving.

Another thing to consider is tire size. If you are running a big and small tire combination, you can use more rear brake that you do with all tires the same size.

Best braking is when you can get all four tires to the verge of locking up at the same time.

Mac · November 10, 2009, 10:58:14 PM

Thanks E-Joe. Insightful theory there. "Teach a man to fish"
I know I want to replicate the brake system from 70's (maybe into the 80's) vintage C-10's. I think the rotors and calipers from the upgrade kit I bought are mid 70 ish.
I was hoping someone could quote from a source like Hollander, etc. that "yeah, the same valve is used on full size Chev, BOP, GMC, whatever, from 19XX to 19XX". I'd like to expand the hunting ground if I can.

wayne petty · November 11, 2009, 02:07:40 AM

http://www.piratejack.net/Proportioning-Valves.html

i know i posted this a long time ago.. but..

Bruce Dorsi · November 11, 2009, 06:15:13 AM

Quote from: "enjenjo"Lets try to clear the valves up a bit.

The first is as a hold off valve. Since the rear brakes are kept tight to the drum, they don't have to move much to apply. On the other hand disc brakes at the front are pushed back from the rotor by flex in the parts, and in some cases the seal pulls them back a bit. So the hold off valve keeps the rear brakes from applying until the front brakes are applied. It makes it stop straighter, and keeps the rear tires from locking up.

I respectfully disagree, Frank.

I have always thought that the hold-off valve, aka "metering" valve is to prevent the FRONT discs from applying until the REAR drums are applied.

Since I don't trust my memory, I just looked it up.

According to ECI: "These valves are used for the front disc brakes in a
disc/drum braking system to provide a "hold-off" feature so as to
allow the rear drum brakes to actuate first. This function is essential for correct system operation."

According to MP Brakes: "Metering valves are needed in the front disc
portion of a disc/drum system to retard the application of front disc
brakes. Without them, cars will nose dive and you will experience
excessive pad wear.

enjenjo · November 11, 2009, 06:34:19 AM

Quote from: "Bruce Dorsi"
Quote from: "enjenjo"Lets try to clear the valves up a bit.

The first is as a hold off valve. Since the rear brakes are kept tight to the drum, they don't have to move much to apply. On the other hand disc brakes at the front are pushed back from the rotor by flex in the parts, and in some cases the seal pulls them back a bit. So the hold off valve keeps the rear brakes from applying until the front brakes are applied. It makes it stop straighter, and keeps the rear tires from locking up.

I respectfully disagree, Frank.

I have always thought that the hold-off valve, aka "metering" valve is to prevent the FRONT discs from applying until the REAR drums are applied.

Since I don't trust my memory, I just looked it up.

According to ECI: "These valves are used for the front disc brakes in a
disc/drum braking system to provide a "hold-off" feature so as to
allow the rear drum brakes to actuate first. This function is essential for correct system operation."

According to MP Brakes: "Metering valves are needed in the front disc
portion of a disc/drum system to retard the application of front disc
brakes. Without them, cars will nose dive and you will experience
excessive pad wear.

I will defer to your references. I understood how it functions, but did not consider the effect.

enjenjo · November 11, 2009, 06:42:17 AM

Quote from: "Mac"Thanks E-Joe. Insightful theory there. "Teach a man to fish"
I know I want to replicate the brake system from 70's (maybe into the 80's) vintage C-10's. I think the rotors and calipers from the upgrade kit I bought are mid 70 ish.
I was hoping someone could quote from a source like Hollander, etc. that "yeah, the same valve is used on full size Chev, BOP, GMC, whatever, from 19XX to 19XX". I'd like to expand the hunting ground if I can.

I don't think you will have a problem using any valve from a C10 from 73 to 87. I think the application is wider than that but I have mixed those partrs in the past with no ill effects.

Mac · November 11, 2009, 11:52:35 AM

Quote from: "enjenjo"
I don't think you will have a problem using any valve from a C10 from 73 to 87. I think the application is wider than that but I have mixed those partrs in the past with no ill effects.

Thanks again.
I was starting to get the idea that I don't have to be so particular about selection. The PirateJack site Wayne pointed to (thanks Wayne) shows a choice of generic valves by disc/drum and disc/disc in brass, alum.,or chrome.

38HAULR · November 11, 2009, 03:32:22 PM

Residual pressure valve . Rubberized , sits under the m/cyl line seat in drum applications. In Disc/drum it is discarded in the disc line.As enjenjo mentioned ,the caliper pistons return , the return is actually due to flexing of the piston seal,this actually forces fluid back to the m/cyl. When doing a disc conversion,leaving this in will have your front pads holding on.
Drum brakes retain some line pressure due to the residual pressure valve,this is counter acted by the spring that pulls the shoes back.
Ideally in a brake situation the fronts should lock just before the rears,this reduces the tendency of finding the rear end of your vehicle whipping out and "overtaking "you under panic braking.
Balanced braking is what we need for safety,best practice to use the right combo of disc/drum with the right selection of components from m/cyl bore/caliper bore /wheel cyl bore,and use an adjustable prop valve for fine tuning.
Sometimes transplanting a brake system from one vehicle to another ,is not ideal if the weight distribution of the vehicles is different.
Frank.