Proportioning valve question
 

I,am doing a power drum brake conversion on my 70 c10 and was wodering if the porportioning valve is the same for manuel brakes as power brakes. All help is appreciated
thanks
bob

Re: Proportioning valve question
 

Yes

Re: Proportioning valve question
 

Note that power brakes systems have different wheel cylinders and master cylinders (the bores are different sizes). Are you changing those over at the same time?

Re: Proportioning valve question
 

Yes, doing 100 per cent brake job. ALL THAT IS OFFERED FOR WHEEL CYLINDERS IS STD AND FOR THE H/D BIG SHOE BRAKES

Re: Proportioning valve question
 

My understanding of the proportioning valve is it's only used for disc brakes and drums together not for both drums.

Google:
A proportioning valve is a valve that relies on the statics to supply a reduced pressure to an output line. A simple example is where spring load applies a reducing force so that the output pressure is reduced. Proportioning valves are frequently used in cars to reduce the brake fluid pressure to the rear brakes.:chevy:

Re: Proportioning valve question
 

Drum brake trucks have a distribution block.
The 71-87 disc brake trucks have a proportion valve.
Just add the brake booster to your current M/C.
Done.

Re: Proportioning valve question
 

thanks fellas

Re: Proportioning valve question
 

I'm following this one, let us know how and what you end up doing, I plan on doing the same, Joe..

Re: Proportioning valve question
 

Yes - The thing already on your truck that is installed between the master cylinder and the wheels, that the brake lines go into and out of, can be reused for your power brake conversion.

Re: Proportioning valve question
 

I,am just going to reinstall it like it was except with a booster

Re: Proportioning valve question
 

That's what we did on our 68 it works find. A lot improvement over no booster. Powered the drums brakes. We left the original valve in place. Brakes work a lot better.

Re: Proportioning valve question
 

That's what I did on the ramp truck.:chevy:

Re: Proportioning valve question
 

Not to hijack the thread but are those booster brackets hard to come by?

Re: Proportioning valve question
 

Usually an easy pick from one of the many truck being parted on the parts board. Sometimes sellers prefer to sell with the booster which adds weight and cost, but understandable if all is in good condition. Captainfab also sells a custom one that tucks in closer to the firewall - but it may require some thinking as far as the pushrod arrangement - ask the good Captain, he will know exactly what you need. But if you want original, a truck being parted or a WTB ad would produce results rather quickly I'd imagine.

Re: Proportioning valve question
 

Andy4639 , did you use any booster support braces

Re: Proportioning valve question
 

No what you see is all I used. The truck that I got it off of didn't have them either.

My 71 factory setup doesn't have it either.

The block on the master cylinder is just a distribution block & brake light hookup and not a porportioning valve.

Disc to disc and drum to drum don't need them.:chevy:

Re: Proportioning valve question
 

Thanks, do the 71-87 trucks with proportioning valves still run the brown wire to the brake idiot light in the gauge cluster and the proportioning valve?

I have a basket case '71 GMC (it's a '71 cab on a '69 chassis) hence my question

Re: Proportioning valve question
 

71-72 do, can’t speak for 73 and up definitively.

Re: Proportioning valve question
 

HEY! That looks familiar! Genuine LowLion parts on the Ramp Rat!

Re: Proportioning valve question
 

a bit old but as i search this thread is most recent. I am finding that the valve in question is called a combination valve(per service manual). this seems to indicate that this is another name for proportioning valve?
Please correct any thinking here as I am trying to get my head around doing my brakes correctly and safely.
It is my understanding that with front disc and rear drums the front need to be limited until the rear brake can overcome the pull back springs.

my truck is missing its valve and I have purchased one online new. Problem is it has an extra port (two) for the front. Can I plug one or should I get a different combination/metering valve?

Re: Proportioning valve question
 

it may be Combination Valve for drum brakes, Proportioning Valve for disc brakes. Jump on AutoZone's website or RockAuto and see if they sell both for say the 1971 model year, just an idea.

Re: Proportioning valve question
 

thanks. I bought what was listed specific for my model(front disc rear drums) everything i found was for two front lines. I hate to buy used because it sounds like they are a pain to reset if tripped.
I am OK running two front lines but would be happier to leave all as is, if possible, and just add a combination valve.

Re: Proportioning valve question
 

I don't understand why the English language is such a challenge for some on this board. Actually, not just this board, but throughout the automotive world.

com·bi·na·tion
/ˌkämbəˈnāSH(ə)n/

noun: combination; plural noun: combinations
1. a joining or merging of different parts or qualities in which the component elements are individually distinct.
"a combination of blackberries, raspberries, and rhubarb"

An automotive COMBINATION VALVE is THREE valves COMBINED into ONE unit. It is comprised of a Metering Valve, a Pressure Differential Switch and a Proportion Valve. Each of those three items serve different functions.

A Pressure Differential Switch that Andy showed you is a stand alone unit, that turns on the dash warning light and nothing else.
A Pressure Differential Switch in some form, is used on dual brake systems with drum/drum and disc/drum and disc/disc. It is used with power and non-power systems.

The first picture is a Combination Valve.
The second picture is the exact same thing, but as three individual units. This requires a lot of plumbing.

Re: Proportioning valve question
 

you missed a part but thanks for trying

"my truck is missing its combination valve(service manuals words not mine) and I have purchased one online new. Problem is it has an extra port (two) for the front. Can I plug one or should I get a different combination/metering valve?"

i will search further this evening for a better match when time is available but thought someone might have a quick answer to the outlets in question. but thanks anyways.so far they all come up with a valve that appears to separate outlets to the front brakes. but my math is simple too so i could be wrong.;)

Re: Proportioning valve question
 

The OE style combination valves have 2 front outlets that are typically plumbed directly to the left & right front calipers. But the front brake line plumbing in 71 & 72 trucks includes an inline Tee fitting so only one front outlet is needed. You can safely plug the other unused front outlet with an inverted flare plug. In fact, I believe the factory installation used a plug (rather than a special single-outlet combo valve) for the 71 & 72 trucks.