Disc Brake Proportioning Valve

[rmcbama]

I just spent a few hours searching history about the Chevy disc brake conversion and found everything I needed but didn't see anything on the proportioning valve. I just installed the JBG disc brake conversion (last purchase from those guys, another story) on my 68 and plan on running an unassisted Master Cylinder, spring and ball check removed. Can I use the original proportioning valve or need another one? If a different valve is called out which one should I use? I'm running the new discs on the front and original drums on the rear. I've heard from several that the power assist provided little improvement for the cost over just adding the discs.

 

[broncomitch]

disc's can handle ALOT more psi the the drums can cus it would just blow the seals off,
so that's what the proportoning valve dose,keep's the psi down so the seals wont blow out on the drums.

get one for a 76-77 EB or get the one's off of a full size bronco.


im still running my stock drum/drum valve and i have disc brakes front and back with a booster, it stops ok for having 38's on it. ill be getting a proportoning valve off a late 70's lincoln continental cus it had disc brakes front and rear.

 

[broncnaz]

The only time you need a proportioning valve is if your rear brakes are locking up before the fronts.
The stock drum/drum H block is not a valve its only there for the brake warning light. many people have used it without any issues. I still run mine with front discs.

Power assist only makes the pedal feel softer it really doesnt improve braking any. Some people that run H boost do see improvements due to the fact that there brake system is not quite right to begin with as they had a hard pedal with little braking the H boost again lessens the pedal effort but also adds a lot of extra force to the MC which can improve brakes in that situation although I would really want my brakes working as best they can without any type of power booster.

 

[TBS-POPS]

Mitch, the worst thing you can do is give bad info so dont give any at all if your really not sure... the prop valve has nothing to do with blowing out the seals....

A proportioning valve cuts down the pressure to the rear drum brakes to keep them from locking up before the front discs do. It takes more pressure to run discs than drums. But some have run (such as I) front discs/rear drums on the stock h-block with no adverse effect. It all depends on what master cyl and which brakes your running.
As far as adding power brakes, That all depends on how much pressure you are willing to live with pushing on the brake pedal. Sitting at a stop light with an auto trans can get tireing pushing hard on the brakes to keep your rig from kreeping or decending downhill with tires over 33's and trying to hold things back can get pretty tiresom without power brakes. I put front discs on before i went to power brakes and it all worked very well under normal conditions. Addind power just made things ALOT nicer!
Back to a prop valve, try the front discs with the stock h-block first,It has no proportioning effects, it might work fine. If the rears keep locking first then an adjustable valve from Willwood can be added to the rear line real easy and you can fine tune the rear braking better... or any of the Bronco houses sell the appropreate valve.. ripping one off a lincoln or anything other than a 76-77 eb would not be advised because the rate of proportion would not be correct...

 

[Buldozer]

Like the good advise others have given you, you only need a proportioning valve if your back brakes are locking up before the front....if that does occur, you can choose to leave the front line direct and install a simple adjustable proportioning valve like this inexpensive one from summit.

http://www.summitracing.com/parts/SUM-G3905/

It will work just fine, and you can fine tune it until your back just stops locking up, which is how I like mine adjusted. Then later on if you change tire sizes, add disc brakes to the back, add a power booster or any other modification that changes the balance, you can just readjust the balance so that the back just doesn't quite lock up before the front again and your good to go.

Good luck!

 

[fordtrucks4ever]

Well lets get it right this time. A proportioning valve does not cut down the pressure going to the rear brake. Bad information is just as useless as misinformation.



A proportioning valve is only for the rear brakes. Doesnt matter if disc or drum, it only provides for control of the rate of pressure rise to the rear brakes. Just the rate at which it builds up. The rear brakes will see full master cylinder pressure. Just not soon as the fronts.

When you apply brakes while in forward motion, the front end will nose down causing reduction of weight on rear wheels. By delaying rate of pressure rise, it eases the application of the rear brakes helping prevent rear wheel lockup.