Anyone knows what the combination valve does besides trigger the brake light on the dash when the pressure is unequal or low? I heard people call it a metering valve or proportioning valve. the one on the 71 Camaro drag car is leaking. I just wanted to do away with it and put one of the adjustable wilwood proportioning valves for the front. I also notice the front wheels are hard to spin. Just replace the hoses and the master. Could it be this combo valve? I don't think its the calipers. Those are kind of new too. And wheel bearings are not on extra tight or anything like that. As far as the brakes, front has factory discs and rear has a narrowed dana 60 with some kind of mopar drum brakes. Thank you all for the help.

Jay

The stock disc/drum 1971 combination valve has a metering valve And a proportioning valve And a brake light switch inside it, hence "combination".

The metering part is for the front brakes. It delays front brake action.

Proportioning is for the rear. It reduces rear line pressure in proportion to the front during hard stops.

In your case, since it is leaking, it needs replaced. The adjustable one should do okay for you. It goes in the rear line only, and so has no delay for the front brakes... so you might overuse the fronts during light street braking. And I would stay away from ice and snow.

If you suspect anything above the calipers is causing brake drag, the brakes, while dragging, will release upon opening the bleeder screw. Both sides would release at once if it is the valve, the line to the valve, or a master or booster or pushrod/pedal problem. If it is line or hose blockage below the valve, only the one side would release.

If they dont release, it could be a caliper or hardware problem, excessive rotor runout, or possibly something I'm not thinking of.

edit: Not all combination valves had all functions. Now that I think of it, the 71-74 Fbody valve might not have had any rear proportioning inside, same as manual disc and wagon Abody.
But you don't have stock rear brakes, so they might or not need one

The Camaro is a race only car so I won't ever need to worry about ice snow. But it is a bracket racer. So I do hit the brakes hard at the top end. The front tires always locks up. We went through 3 sets in the last 2 years. I wonder if it could be because they are skinnies, but what else could I do? I was thinking to lower the pressure to the front so they don't hit as hard and lock up. But then again, if it's dragging already, then the lock up problem may go away when I fix it. Hope so. Any other suggestions on what I should do? Thanks for all the help so far.

Jay

Once you fix the dragging brakes problem and the leak, if the fronts lock before the rears, and all else is in good repair, you need to balance the brakes better for your application. A prop valve will only reduce rear pressure even more.

This might mean getting larger rear brakes, smaller front brakes, or both... or maybe something else in your case. You have to know what you have now, and it's effect, before you start changing things. Dont change too much at once.

Since drag racing is basically a one stop deal, you dont have to worry as much about brake fade, so I would concentrate on hydraulics. Find the diameter of your existing front and rear cylinder pistons, and change them if needed, for balance in your drag racing application. This might mean a change in master cylinder too. There are usually bolt-on calipers and wheel cyls with different size pistons for most applications.

Here are a few articles you might be interested in.
http://thebrakeman.com/valvetechii
(the last 2 graphs are messed up because they are just the same as the 2nd, but it is a good article anyway, as was valvetech I (http://thebrakeman.com/valvetechi). There are more from him you might like, but I have not read:
http://thebrakeman.com/articles

Also, StopTech has some good info:
http://www.stoptech.com/whitepapers/brakebiasandperformance.htm
http://www.stoptech.com/whitepapers/proportioning_valves.htm
http://www.stoptech.com/technical/

Hope this helps some.

Thanks Chevry. I'll check out those sites ASAP. I hope its just the valve. I'll let you know how it goes. Probably won't get to it till next weekend.


Jay

Some of the companies that sleeve calipers can also rebuild these units. John Stewart, 349 Millen Rd. N., Stoney Creek, Ontario 1-800-309-1995 is one who can do the job.