I have a 73 with stock front disc n rear drums i just converted the rear to disc n added an adjustable proportioning valve. My stock distribution/prop valve is bad n so i thought instead of buying a new one i will do my own distributing with a brake line t for fronts n union for the rear where it would normally hook up at the stock valve n do the proportioning of the rear disc with the adjustable valve i added. I understand that if i loose pressure in one system i wont have a shuttle valve to move n block the flow in the failed system. But other than that does anyone see a reason this wont work

 

It will work by plumbing it the way you stated, BUT--What about your brake fail light???

No Light if you loss pressure, you die, or worse yet kill a innocent person.

Next Question?? Why in the world did you eliminate, or want to the stock block with the PropOrtioning valve in it? Was it that bad?

If it was, rebuild it, it will work PERFECT in your build.

Dan @ Chockostang

 

Well i do have emergency brakes on the rear disc upgrade for backup. I rebuilt the valve following musclecar research instructions n it still wont stay centered the bores didnt look bad but ive bled the crap out of the brakes fllowing the manual i bled the master cylinder n valve then right rear left rear front right then front left. I even unbolted rear calipers and angled bleaders to 12 oclock position n the valve wont stay centered n when i would get it to center the brakes sucked soft pedal. Ive checked n checked n i dont have any leaks. Its all new stainless lines new calipers new literally every last thing but that valve. My thought was before i spent the money on a new valve i could bypass it and if everything works correctly i know its the valve thats the problem before i throw away a hundred bucks. It cost me 10 bucks to bypass it im gonna do it tomorrow n see if it fixes my problem.

 

I literally bled 12 ounces out of each caliper n when you pump the brakes while moving slowly in drive way theyll get real hard n do nothing

 

Just found this it confirms im not crazy

 

Probably just an ignorant observation, here, but, what the heck, it's not the first ignorant thought I've had since getting up this morning. If you have disk brakes on the front of the car and now have disk brakes on the rear of the car, why do you need a proportioning valve anyway. If you are asking about simply bypassing your existing proportioning valve, okay, fine, just plug the rear brake inlet and outlet on the distribution block and hook the rear brake line directly to the master cylinder. Or simply get a distribution block from a drum/drum brake car.

 

Proportioning Valves are installed in cars with Front Disc Brakes. The rear brakes can be either-Drum or Disc, it's does make any difference.

The reason for a proportioning valve in the rear brake line is to SLOW Down the sudden flow of pressure to the rear brakes in a Panic Stopping situation.

But why with Front Disc only???? Reason is weight transfer. With the much better bite/stopping power of Disc brakes, the nose dives, the rear rises taking weight of the tire. This transfer of weight will cause the tires to lock up, thus the driver having no control.

The Proportioning valve stops this by that millisecond stopping of the pressure to the rear brakes.

The rears will lock up with Disc or Drum with this weight transfer.


Dan @ Chockostang

 

Another question for you Dan. Do i need a bigger master cylinder with a bigger bore to compensate for the rear disk brakes I added

 

Very Doubtfull, Bigger is not always better in a master cylinder.

Dan @ Chockostang

 

Think i got the problem narrowed diwn to a bad master cylinder. I pulked it off n actuated it n lota fluid squirts from rear lines outlet n just a little from front lines outlet gonna change tomorrow