brake question

[30 a truck]

Is this a proportioning vale or a distribution block? It has 2 inlets & 2 outlets.

[RodnRudy]

Definitely a distribution block.

[67 chevelle]

yes and yes and yes , and warning light switch also , commonly called a combination valve

[30 a truck]

So if I don't care about a warning light, it is scrap iron, correct??

[RodnRudy]

Correct, the warning light is for if you lose brake pressure on front or rear.
Make sure you plumb the rear brake line to the master cylinder reservoir closest to the mounting flange.

[Mike C]

For a 4 wheel drum vehicle on top of the other responses.

[30 a truck]

Mike C, Can you explain? It was on a disc/drum truck.

[67 chevelle]

Originally Posted by 30 a truck

So if I don't care about a warning light, it is scrap iron, correct??

Definatly no ,, must be used ,, if your front brakes go out it redistributes the fluid to the rear giving you brakes , instead of losing pressure in the whole system and having no brakes ,, also you want a warning light

[frankslagoon]

Interesting discussion. So I thought the dual master cly. would only bleed frt. or rear and still give ya fluid to the end that didn't have a leak. Does this function take place at the master cly or the valve. if it's the valve why can.t we just put a valve on the single resivoir trks

[Stocker]

Originally Posted by Mike C

For a 4 wheel drum vehicle on top of the other responses.

Originally Posted by 30 a truck

Mike C, Can you explain? It was on a disc/drum truck.

Disc/drum typically has a proportioning valve, to send required higher pressure to front discs. Drum/drum will use a distribution block instead, and front & rear pressure will be the same.

[frankslagoon]

Well I get that, but the dual master cly is still two separate hyd. systems, right?

[davepl]

It is but a drum is self-assisting and a disc is not, they require different amounts of pressure, I think. I presume one end of the truck wasn't working well, but they might have just felt the front under-assisted or something.

Generally not the hot ticket to use the drum/drum combo valve, but I can't say I've done it so don't know the ramificiations.

[frankslagoon]

I'm sure we need a proportioning valve for disc/drum but I'm betten the only thing the valve does on a drum/drum is set off the light. Now on the older trks with single res. they use different size lines from frt to rr. to limit amount of pressure to rear so they don.t lock up first because of weight transfer

[30 a truck]

Truck had no proportioning valve, only this distribution block. It was a disc/drum when I purchased it. Granted it was disassembled, but all the lines were still in place.

[frankslagoon]

If your putten it on a disc brake system then I'm pretty sure ya need the valve.I don't think ya can use a disc brake master cly. on a drum brake trk.

[67 chevelle]

There are 3 types ,drum drum ,disc drum , disc disc

[frankslagoon]

Originally Posted by 67 chevelle

There are 3 types ,drum drum ,disc drum , disc disc

So my question is, does the dual master cly. segregate the frt and rear or does the valve do it?

[Stocker]

Originally Posted by frankslagoon

So my question is, does the dual master cly. segregate the frt and rear or does the valve do it?

The dual MC does it. There's a reservoir for front brakes... the other reservoir is for rear brakes. The proportioning valve is there to supply higher line pressure to the front discs, and lower pressure to the rear drums. And of course to light up your "Brake" warning light if pressure is lost in either front or rear system.

[67 chevelle]

Both do actually , but if you remove the combo valve and put in a tee , both reservoirs will dump out the lowest pressure , ie hole , and you will have no brakes at all , where as if you keep the combo valve , or run separate lines for a front and rear with no tee [ill advised] you will have pressure in the front or back if you blow a hole in the other .

Best and safest to run a disc drum dual reservoir , or 4 disc's with combo valve and emergency brakes , you cant go unless you can stop , great brakes are the beginning of a build , 80 percent of braking load is on the front .

[30 a truck]

I am running a dual reservoir. What is wrong with 2 separate lines? I am trying to learn something.

[frankslagoon]

Dual resavior seperate lines to drum brakes shouldnt need valve except for light right?

[RodnRudy]

The purpose of the proportioning valve in a disc/drum application is to provide about 60% less braking application to the rear after you step on the brake pedal. It also has a 30PSI delay rear to front circuit. What this does is allow the rear brakes to energize slightly before the front to promote anti dive. After brakes are applied the front brakes have the 60% braking force.
The master cylinder piston for the rear reservoir energizes before the front so the rear brakes are applied first. That is why it is important to plumb the rear m/c reservoir to the top rear fitting on the proportioning valve.

[frankslagoon]

I understand how the disc/drum system works. My question is do we need a valve in a drum/drum setup?

[Mike C]

Usually drum/drum setups were balanced by changing size of the wheel cylinders front to rear. In the '67-'69 Camaros there was an additional component added to the rear brakes in addition to the drum distribution valve like the pic you posted. But the factory 71-72 setup should have a combination valve which will have two lines coming off for the front brakes and one for the rear.

It's been awhile since I messed with a drum/drum setup. There is a total of 4 openings correct? One front in, one front out, one rear in, and one rear out.

I may have to go look at my combo valve since I don't remember exactly how it looks now.

[30 a truck]

Total of 4 openings, front in, front out, rear in, rear out.

Probably going to get a real proportioning valve & do away with the distribution block.