Desperate - Brake problem

I've got a major brake problem. Here's the story.

The problem involves the metering valve in the proportioning valve.

I put Ford caliper brakes on the 8 1/4 a few years back and had lots of problems.
What happend was, the brakes felt great during the first 5 minutes or so of use. After driving for awhile and using the brakes, the front brakes would build up pressure. The more the brakes were used the tighter they got until they were close to a lock up. (One time the did lock up).

I did all the proportioning valve mods and still, I continually locked up the front brakes. I burned up pads and calipers on a regular basis. I even tried the ZJ proportioning valve and for a while, it seemed to work. In the end, I finally had to install a manual proportioning valve to solve the problem and has been great for a year now.

Recently, I installed a 8 3/4 axle with 11" drum brakes, and I backed the manual proportioning valve down to mininum. Everything worked great but I had a severe right hand pull with normal braking. I checked everything and replaced the front pads, calipers and hoses. The rear brakes were completely new and fully checked out.

Finally I decided to remove the manual proportioning valve and reassembled the OEM metering valve. I pressure bled the system and the breaks felt great.
Now I'm back to the brakes feel great during the first 5 minutes or so of use. After driving for awhile and using the brakes, the front brakes will build up pressure. The more the brakes are used the tighter they get until they are close to a lock up and severely hot.

I've spent countless hours now trying to resolve this issue and I've now got 5 days to solve it since my 2 week vacation is coming up. I really need help.

I'm fairly certain I reassembled the metering valve correctly (referred to GoJeeps site) and I'm willing to replace the entire proportioning valve if necessary. I just want to make sure it's what is needed to do before I incur more expenses.

If my understanding is correct from memory if your breaks get that hot from dragging then you can boil the fluid in the caliper and introduce gas bubbles or air. If your front calipers ar sticking this may be your problem. Did you change them at some point? You may have toasted your master cylinder also from all the bleeding. The master cylinder develops a ridge where the piston normally stops. When you open a bleeder you can push the piston in the master cylinder beyond this ridge and bugger up the seal on the piston. If you pull the spring and o-ring out of a stock proportioning valve you should have your rear end locking up befor the front thus basically eliminateing the proportioning valve for trouble shooting. The only other thing I can tell you is that I had to park my jeep nose down to get a good bleed on them because of my rotated ford rear end pinion.

Stumpalump said:

If my understanding is correct from memory if your breaks get that hot from dragging then you can boil the fluid in the caliper and introduce gas bubbles or air. If your front calipers ar sticking this may be your problem.

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At this point I haven't allowed the brakes to get that hot (several years ago that did happen)

Did you change them at some point?

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As of yesterday,front new calipers, pads and lines.

You may have toasted your master cylinder also from all the bleeding. The master cylinder develops a ridge where the piston normally stops. When you open a bleeder you can push the piston in the master cylinder beyond this ridge and bugger up the seal on the piston.

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That's what's nice about a pressure bleeder, doesn't cause this to happen.

If you pull the spring and o-ring out of a stock proportioning valve you should have your rear end locking up befor the front thus basically eliminateing the proportioning valve for trouble shooting.

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That is correct for the proportioning valve, but the metering valve is what effects the brake front to rear ratio. Technically, when I release the brakes from applying them, the metering valve should return to it's normal position and should 'pull' the fluid back, removing the pressure from the brakes (at least that's how I understand the process). It seems this is happening to the rear, but not the front.

Thanks for the reply.

Metering valve and proportining valve are not the same thing? I think the metering valve is controled by a proportioning spring and the whole thing is refered to as a proportioning valve. Correct me if Im wrong. Do your front pads drag with the new calipers? Dumb question and probably not your problem but could you have a pinched hard line on the front? Is your break pedal comming all the way back up or is the rod going into the master cylinder or booster too long?

Stumpalump said:

Metering valve and proportining valve are not the same thing? I think the metering valve is controled by a proportioning spring and the whole thing is refered to as a proportioning valve. Correct me if Im wrong.

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That is correct.

Do your front pads drag with the new calipers?

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When set up fresh, I can drive around 1/2 hr and the brakes feel great. Let it set overnight and within 15 minutes of driving, they start to tighten up.

Dumb question and probably not your problem but could you have a pinched hard line on the front?

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Both are brand new.

Is your break pedal comming all the way back up

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yes

or is the rod going into the master cylinder or booster too long?

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Something I want to check.

My Jeep has been setting in the parking lot since 8:30. I was going to lunch, so as I backed out I noticed the pedal was high. My last episode a year ago, taught me I could loosen the proportioning valve bleeder past the 'O' ring and bleed the pressure off to give me some pedal. I just did this and went to lunch, using the pedal only once (coasted, dropped into low gear and used ebrake). The Jeep sat for 1/2 hour for lunch and I came back out and the pedal was high again. I bled the prop valve again and this time I was able to get back to work without touching the brake pedal. By time I got back to work the brakes were dragging heavily again. It seems, the engine heat is causing the fluid to expand. I'm chilling some water right now and plan on pouring the cold water on the prop valve just to see if it makes any difference. None of this is making any sense.

If the push rod between the MC and the booster is slightly too long; RE: just touching, the brakes can build up pressure in the front circuit, and cause the problem you're experiencing.

xjbubba said:

If the push rod between the MC and the booster is slightly too long; RE: just touching, the brakes can build up pressure in the front circuit, and cause the problem you're experiencing.

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Thanks guys. Another direction to try. I'll back it off one turn as soon as I can nurse this thing home and see what happens.

Have you ever checked your brake booster? Maybe try and drive your jeep with the engine off (if you can safely do that) then try the brakes and see if you have the same symptoms. This kind of sounds like when you build up pressure and then you slightly press the pedal the brakes lock up. It sounds like you know more about brakes than me, but I would suggest trying that.

Thanks everyone. The push rod was the problem. Took awhile to find the sweet spot on the adjustment, but the braking system is now working like a charm.