A question for the experts,

I've read that the proportioning valve/distribution block on a drum/drum system sends the same amount of fluid to both the front and rear brakes. So, what does this valve actually do besides house the brake failure light switch? Is there anything really wrong with just plumbing your brakes straight from the Master cylinder to a front splitter that will then run two separate lines to the front left & front right wheel cylinders, and from the master to the splitter in the rear, since the brake failure light switch isn't working anyhow? Seems like the easiest fix since the 1970 4x2 drum/drum "brake pressure differential proportioning valve-C8TZ-2B257-D" is obsolete? This is my first project, any insight is much appreciated. I know most of you guys are in favor of swapping off a donor for power disks, but I'm confident that the HD drum/drum system should be plenty of stopping power for the type of use I'm looking to get out of my truck, I am just in the process of rebuilding the brakes now and I am looking to replace all of the old equipment.
Thanks,
Matt

 

So, where did you read that, pretty sure if Ford designed it with the valve it's needed. I believe the front would have more braking power, less in the back. Back tires would lock up as there is limited weight on them.

Running over that family going to the mall would ruin your day.

 

It makes sure that if you lose a brake line you don't lose all your brakes. You will still have front or rear. Definitely keep it in there. They are both get the same pressure because you don't have disc brakes. Disc brakes require more fluid.

 

I read that all systems that are drum/drum get the same amount of fluid to each wheel cylinder, unlike disc/drum setups that get more juice sent to the front discs, which means all the distribution block/proportioning valve does is separate or "distribute" the fluid to each cylinder, but doesn't necessarily "proportion" it differently. Perhaps ford still put that distribution block/proportioning valve there, not necessarily because you need it, but because it was the easiest/cheapest way to keep all the brake lines/failure light switch in the same place for all different brake setups, just by throwing in a db/pv that had different internals but mounted up the same? I don't know if it’s right or not, and I'm not saying I'm right, that’s why I'm asking for other opinions here...But it seems to me that if drum/drum systems really did get an equal amount of juice to each wheel cylinder, then the only real purpose of this item is to house the failure light switch? So does anyone know if it’s true that each wheel cylinder gets the same amount of juice???

Thanks,
Matt
PGH PA

 

Thanks for the reply JB,
I did not know that this item helped keep the front/rear systems separated, I thought that the dual MC reservoirs would keep the rear and front brake fluid levels independent of one another, as long as I plumbed the front reservoir directly to the front brakes and the rear reservoir directly to the rear brakes they would stay independent. That’s why I called upon the advice of seasoned veterans.

Matt

 

On vehicles with disc/drum combinations the valve is needed because disc brakes operate at a higher pressure than drums. Without the proportioning valve the rear drums would continually lock up durring braking.
The brake warning light switch is located in the valve strictly for convenience.
With a drum/drum system you wouldn't NEED a proportioning valve. Case in point, before dual master cylinders, one line came from the master to a "T" mounted on the frame and then branched off from there.

 

Proportioning Valve
The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes.
The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located. If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi.

 

The ford drum/drum "proportioning valves" don't do you you described above. The pressure to front and rear remains equal. Guess what happens when you slam on the brakes on ice or gravel? You guessed it, the rears lock up.

 

That IS the job of the dual circuit master cylinder, NOT the proportioning valve. You had it right, Honkey

 

Thanks devino,
So I could just plumb the brake lines from the MC directly to the front and rear brakes and the only thing I would be losing is the brake failure warning switch (which is currently inoperable anyways)??? I'm just wondering incase my 43 year old pv/db gives me problems when I go to replace all my lines and try her out, since the replacement pv/db is obsolete...
ps all brake hardware has been replaced (wheel cylinders, springs, hoses, MC, shoes, etc....)
Thanks for all the input guys,
Matt aka HonkeyLips-from National Lampoons summer vacation

 

I am fairly sure that Armstrong is still correct, I know what you are planning to do will work per say, but there is a purpose for that proportioning valve. That said I also know finding one is near impossible without going aftermarket. Just remember that the back brakes will lock up alot sooner without that valve, just be mindful and you should be ok

 

The proportioning valve is a safety switch too. When you loose all pressure to the front or rear there is a valve inside that shuts off the side that lost pressure. Do not run without one.

It would be more appropriate to replace it with an adjustable prop valve from say wilwood. That would allow you to turn down or up the rear brake power for towing or slippery conditions.

 

Umm, no. See my above post.

 

Ok then what is the point of the sliding valve in the proportioning valve?
I think you are only partialy correct. Yes I understand that there is a split master cylinder. Older cars and trucks used to run without a prop valve. The prop valve lessens the pressure to the rear brakes under normal conditions and is also a failsafe switch. When there is a pressure differential beyond a certain point it flips the valve and turns on the brake warning light.

 

This very subject is being discussed in another thread and all of these questions have been answered and explained.
https://www.ford-trucks.com/forums/1...atibility.html