Proportioning Valve Maybe?

Replaced a busted wheel cylinder this weekend and new brake shoes. Bled the fuel lines and at the front when I open the bleed screw I get a solid squirt/stream of fluid. But at the back I only get an ooze of brake fluid. I would think the rear brake shoes get a little less fluid pressure than the front discs but it seems like I should have more at the rear than just an ooze of fluid at the bleeder screw. So is that normal or could I possibly have problems? Maybe a bad pro portioning valve or master cylinder or something?

 

May need to reset the proportioning valve. Sometimes bleeding a front wheel will center the valve and return flow to the rear.

 

With drum brakes on rear, I wouldn't expect to see any pressure on the line bleeder.

 

I wouldn't say I tried bleeding the fronts but I did open the bleed screws on both front wheels with the brakes pumped up and held. No air...just good fluid flow. I didn't bleed much because there wasn't any air so it didn't seem like it needed bleeding. I don't know anything about how the proportioning valve works but are you saying maybe I need to let a little fluid pump through the fronts to re-center the proportioning valve somehow?

 

That is correct. Just have someone put a little pressure on the brake pedal and crack a bleeder on the front. Then go back to the rear and try it. A quick google search on resetting proportion valve will probably give better info than I can. There is actually a tool that will hold the valve centered while bleeding or it can be held manually centered if you have one more person to help.

 

That's for the metering valve, not proportioning valve. Otherwise correct if this is on a vehicle with stock drum brakes in the rear and factory discs in front.

 

Oops!

 

That's what we're dealing with Nick. Stock drum brakes on the rear and stock discs on the front. I have a power booster but not sure if it's stock or not. It's an 84 CJ7.

I'm not even sure I know the difference between proportioning valve and metering valve.

So if V.O.'s instructions were for a "metering valve" do I still need to do this? What about the proportioning valve?

 

The metering valve is part of the combination valve. It is on the end of the combination valve (the brass part that both lines from the master cylinder goes to then the lines split and go front and rear). On the end of the combination valve will either be a rubber cap or what looks like a pin sticking out. If the cap is there carefully pull that off and you should see the pin. You need to hold the pin inward by hand if you do not have the correct tool. Do not use a c-clamp or anything like that as you can damage the metering valve. This shouldn't matter to fluid flow to the rear, but for some odd reason sometimes it does have an effect. A metering valve holds off pressure to the front brakes until pressure rises in the rear system (i.e. the brake shoes make contact with the drums and hydraulic pressure starts to rise). Once pressure rises enough in the rear then the front system opens up for full braking. The idea is to balance braking.
The proportioning valve controls pressure to the rear brakes. Only way this would be a problem is if it were stuck closed completely, which is possible.

If your combination valve has an electrical plug on it then it has a pressure differential switch built in. If so that could cause the rear brakes to not get pressure if the valve was moved toward the rear brake system shutting off the fluid flow.

This is really what V.O. was referring to that could block the fluid flow and needing to open a front bleeder to get it to move back to the neutral position allowing fluid flow to the rear.

I didn't have time to type this all out before so shortcutted my earlier post, which technically wasn't correct either.
All these valves, pressure differential switch, metering valve, and proportioning valve are all in the brass block I mentioned earlier and not individually serviceable.

I would suggest loosening the hydraulic line somewhere in the rear circuit before the hose and see if you get good flow. If you do, and still cannot get flow out of the wheel cylinders then the obstruction is after the combination valve. A hose like Walt mentioned or maybe bleeder valves plugged/partially plugged, etc.
If not then it has to be in the combination valve or master cylinder.

 

I'm beginning to slightly understand but I'll read this again tomorrow before I attempt anything. I think what I've always called a proportioning valve must have actually been a multipurpose group of valves in a single assembly.

On the wire and brake light. Yep my brake light in the gauge cluster is stuck on. I've never even seen it lit up before. Didn't even know I had a brake light till this issue came up.

 

I went and took some pictures Nick but I can't upload it. Working from a cell phone. Reckon you could send a text to my cell at 601-503-4753? I'll respond with the pictures I just took of the valves.

 

I think I can upload pictures today Nick if I can figure out how to resize them. I see the rubber plug you're talking about. I have the two lines coming from the MC. The wire to the switched is right between these two lines. And I have two lines leaving the valve and going to the front. And I see one single line going to the rear then right above the rear axle there's a "TEE" and that single line splits and goes to each when cylinder. The line runs along the top of the axle.

There are a couple other lines there that are fuel lines. One line is a fuel return line and one connects the fuel tank to the vacuum cannister. Had no idea that was the case.

 

Here are a couple pics Nick. Sorry to be beating this dead horse. I just want to be sure I understand. Sounds like I need to try a few things.

first...basically just blead the front brakes a little bit more. I'm thinking this will release pressure on the front and maybe allow the valve to re-center.
second...go back to the rear brakes and open a bleeder screw and see if that fixes the problem.

What I'm confused about is what do I do when I pull that rubber cap off? Am I supposed to stick my finger in there and try to move a piston, or plunger of some kind? the rubber cap looks kinda small and I'd expect whatever pin is behind there will be even smaller. Seems like if I were to try and move this I'd have to use some sort of wooden dowel or something. The plug appears to only be about 1/4" so I'm guessing the little pin may only be sticking out about the same 1/4". So just push the pin/plunger inside the valve body? do I do that while attempting the bleed?

Also Nick you say to loosen the line somewhere in the rear circuit before the hose. I'm completely lost on this? I have a single hard tubing line coming out of the valve and following the frame rail. It runs into a "Tee" then splits into two lines...one to each wheel cylinder.

 

I think I may have figured it out. The diagrams I saw in the internet refer to the pin as a bleeder rod and I saw some instructions saying to hold it in while bleeding the front brakes only. And not to hold it in while bleeding the rear.

Sounds like a three man job. One to hold the pin in...one to hold pressure on the brake pedal, and one to open the bleeder screw.

Am I getting close?

 

Yes you are. Hope this helps. Brake pressure on both sides of the stem is what holds it centered. With air in the rear brakes the stem shifted and restricted flow to the rear. Pushing the stem in manually allows fluid to pass thru and the rears can be bled. Once all the air is out, the valve recognizes pressure and conditions have been met for it to center.

The method discussed earlier about bleeding at the front with light pressure on the brake pedal will sometimes allow the valve to shift toward the centered position allowing fluid to pass thru to the rear. Light pressure because pressing hard only forces the stem to remain shifted blocking fluid.