need help with non mopar brake issue

[cudaboy]

hey guys. This is not a mopar brake problem, but a brake problem nonetheless and most cars are pretty much the same. I bought an old (86) Toyota 4wd for my son who just turned 16. Got it dirt cheap and have been fixin her up over the last 6 months. the rear brakes were locking up. I replaced the rear shoes, along with new wheel cylinders and new drums. They still locked up. This is an intermitten issue. They'll go awhile with no problem, then next day, lock up again. If you let the truck sit for about 15 mins they free up again. I replaced the rear flexible hose. thought that had it fixed, and then it started doing it again. This truck doesnt have a "normal" proportioning valve in the front like most cars, but has one in the rear called a Load Sensing Proportioning Valve, and it has a rod linkage connected to the rear axle housing to sense the load by how far up to the frame the housing is. This linkage rod was touching the exhaust pipe, so I figured that it was either heating the fluid or keeping the valve out of adjustment. I wired the exhaust pipe up and away from the linkage, and it still locked up. I suspect this valve or the master cylinder. Also, the fluid is BROWN ! Any Ideas?
P.S. This is really urgent becouse he's driving my 01 ram !!!!!LOL

[Butch Romig]

if your brakes are adjusted to tight,it will create heat and make them lock,this may or may not be your problem.also weak return springs can cause this,some of the ricers had a rather odd way of adjusting the ebrake,and that beare looking at also,a gunked up master is also possible
hope this helps
butch

[digdoug]

The first thing I would check isthe master cylinder linkage adjustment. No freeplay is something that can cause what you described. Bleeding out that brown fluid couldn't hurt either.

Doug

[OleRed66]

definitely flush that bad brake fluid out. it sounds like to me that you have some contamination in your fluid that has damaged the brake cylinders or something like that. Anyway, I'd try the fluid and then start replacing parts.

[cudaboy]

Thanx guys. Digdoug, are you saying that no slack in the linkage could prevent the master cylinder plunger from returning to the fully seated position ? Makes sense, but I've never heard of that before. I hope it's something as simple as that. My son will be home this weekend to help me work on it. The first thing I'm gonna do, besides checking that linkage, is to try to make it lock up again. Then I can start at the master cylinder and open the line to see if that releases the brake. if not, I can work my way back to the proportioning valve and so on. If that STILL doesn't reveal a hydraulic problem, I'll take it back apart and replace the return springs. They seemed pretty strong to me, but I prove constantly that I don't know everything !! LOL

[digdoug]

Yes. Good luck ,and keep us posted.

[jonx4x4]

My S-10 had a problem like that. One of my front wheels kept locking up, but not as bad as you describe, just some brake drag.

It turned out to be a flexible hose. Next time it locks up, break the hard line loose at the wheel cylinder. Just enough so that it leaks fluid. Then get back in the truck and see if that set it free. If so, it is a bad soft line. I dont know why, but sometimes when they go bad, they seem to almost have an internal collapse.

I would be willing to put money on this being the problem!

[cudaboy]

Thanks Jon. I already replaced the flexible line on the rear (which is where the problem is) in hopes that it would be that simple, but it did it again. We're gonna go see if we can get it to lock up again, so that I can try the systematic approach I described earlier. I figure that if it doesnt release after getting to the wheel cylinder, that it would be mechanical. That would lead to weak return springs. I'll let ya know. Thanks for the input guys.

[cudaboy]

UPDATE: Drove the truck myself, and it never locked up. Son drove it some and kept it close to home. he came back and said it wasn't locked up but was "trying to". which I interpret as grabbing. So, I popped the hood and cracked the line loose at the master cylinder and it frees up !!!! So that's good news. The bad news is that the master cylinder I had the parts house order for me is the wrong one. The BADDER news is that they don't even stock the one I need to order, AND it costs $125 instead of the $65 that I paid for this one.
The guy at the parts store said it sounded like air in the line to him too, so I held off ordering that expensive part until after we changed the fluid out and bled the system better.
We did all that. It still grabs. So, I think the master cylinder is the culprit.

[cudaboy]

And the winner is......drumroll please....Butch Romig !!! Butch fingered the gunked up master cylinder(maybe I shoulda worded that different) as the guilty party. Look for our courier to bring your prize any day now.
The master cylinder that the first store was going to have to special order and take a week or longer, at $125 (new) was found IN STOCK across the street for only $50(rebuilt) !!
Thanks for all the replies. Now, If your ever driving through Alabama and see a grey primered Toyota 4wd coming toward you...PULL OVER ! Get off the road!