Brakes locked up but nothing looks wrong

On today's episode of what now you needy pig.....

I replaced the entire brake system on Diego a few weeks ago and then a front caliper seized. Fixed that and now I just had a rear brake lock up....

Everything looks perfectly fine. Any ideas? Maybe I just had them slightly too tight but it's been a while without issues???

Has anyone had automatic adjusters OVERTIGHTEN the shoes?

Pictures attached. I don't see anything wrong except for maybe excessive brake dust.



I cleaned everything off with brake cleaner and reassembled. Parking brake is completely released and I don't use it anyway on this truck so it's not like it stuck. I'm stumped with this one. I'm not certain but they might have been smoking last night when I got home, could have just been exhaust I was seeing though.

Left them overnight and they were still locked up. I had to loosen the adjuster to pull the new drum off.

I'm willing to assume that you have everything hooked up correctly. You might want to take pictures of both left and right rear brakes, identical views, to be sure they are the same. Did you replace the wheel cylinders on both sides?

It sounds almost as though the wheel cylinder is not releasing pressure once you step on the brake. That sounds plausible until you remember that the front also locked up recently. That would indicate the possibility that something common to both front and rear is not releasing pressure, holding pressure just enough to lock up a single wheel.

Is this plausible? I'm taking a grab in the dark, and we all know that can be a dangerous move.

Proportioning valve? Maybe?

On double check that the adjusters are going the right direction.

Also make sure to label which photo is left and right, cause that will determine shoe location and adjuster location. I've had them lock up before because I swapped the front and rear shoe before....

Wheel cylinders were replaced as was the master cylinder. The adjusters are on the correct side, and everything was put back the way it was before. Proportioning valve was disassembled and cleaned before putting it on the new master cylinder.

Honestly the only thing I can think is either they over adjusted?

Rears have been working fine for almost two months. I just looked back and it was Sept 11 when I drove it after replacing everything.

Check the backing plates where the shoes ride , for ridges from not being lubed. I had to grind mine smooth once because the shoe was sticking !

SIKPUP said:

Check the backing plates where the shoes ride , for ridges from not being lubed. I had to grind mine smooth once because the shoe was sticking !

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They were ground and lubed when they were replaced in September. Everything still seems to move freely with no binding.

I've seen a master cylinder cause this on front brakes once. At the time I researched other causes and old rubber hoses were also identified as a possible cause. Apparently the rubber can break down and causes the hose to pinch off and act like a check valve.

What did the fluid look like when you flushed it out?

I replaced EVERYTHING. New master cylinder, hoses, hardlines, wheel cylinders, rubber hoses..... Deleted the ABS valve as well.

Everything was filled with brand new DOT4 brake fluid. At this point the only thing I haven't changed is the front hard lines, driver's side caliper and hose, and the booster. I have a new driver's caliper and hose too, just haven't put them on yet. Bought both when the passenger front locked up, specifically because I wasn't sure the hoses weren't the problem so I wanted to eliminate everything else from the equation.

Fluid was nasty brown. I think it might have had some water get into it before as the spring inside the proportioning valve had some rust on it. Not bad, but enough for me to notice. I don't think that could have any effect on this because everything for the rear was replaced together with the master cylinder and lines/hoses.

Hmm. Well, here's an idea, but I'm not sure if it will work. First, see if you can get the brakes to drag in a repeatable manner. Once you generate the condition, pop the bleeder valve at the rear drum and see if fluid comes out slowly, or if there's an initial squirt of pressure. This will tell you if it's coming from line pressure or a mechanical problem at the drum itself. The risk here is that you might put air in the line though.

Supposedly, a faulty booster may also cause dragging brakes but I would expect that to affect all four, not just the rear.

david85 said:

Hmm. Well, here's an idea, but I'm not sure if it will work. First, see if you can get the brakes to drag in a repeatable manner. Once you generate the condition, pop the bleeder valve at the rear drum and see if fluid comes out slowly, or if there's an initial squirt of pressure. This will tell you if it's coming from line pressure or a mechanical problem at the drum itself. The risk here is that you might put air in the line though.

Supposedly, a faulty booster may also cause dragging brakes but I would expect that to affect all four, not just the rear.

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Well I freed it up for now so we'll see if it comes back and I can try it then.

I did that before on the front and fluid certainly does bleed, but no pressure behind it either.

When you get in there again, double check to make sure you have one long shoe on the rear and one short shoe on the front on each side. You would not be the first to put both long shoes on one side and both short on the other side.

chillman88 said:

Has anyone had automatic adjusters OVERTIGHTEN the shoes?

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Here's the answer to this question in a short story. The guy who was my shop foreman/shop manager while I was working on these for a living had a mechanic's shop of his own for about 15 years before he started working at the diesel shop. It was in a small town of just a few hundred people. He had an older lady who was one of his customers. She rarely left town in her car, but did drive it all over town, just about every day. She did a lot of backing up compared to the amount of forward driving that she did. About every 6-8 months, he had to back her rear brakes off because they got to be so tight that the car had a harder time moving. So the answer is yes that can happen. It probably rarely ever happens to anyone.

IDIBRONCO said:

Here's the answer to this question in a short story. The guy who was my shop foreman/shop manager while I was working on these for a living had a mechanic's shop of his own for about 15 years before he started working at the diesel shop. It was in a small town of just a few hundred people. He had an older lady who was one of his customers. She rarely left town in her car, but did drive it all over town, just about every day. She did a lot of backing up compared to the amount of forward driving that she did. About every 6-8 months, he had to back her rear brakes off because they got to be so tight that the car had a harder time moving. So the answer is yes that can happen. It probably rarely ever happens to anyone.

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Okay: story time: my shop teacher in high school owned a shop before he was a teacher and he told a story of a lady that had a old Lincoln or LTD or something and she would bring it in regularly because it was "running rough" and he was the only guy that could straighten it out. Well all she did was creep around town, so as soon as she was gone he'd have one of his mechanics get out on the highway and open it up to blow the carbon deposits out and later that day she'd come pick up her good running car and be set for 6-8 mths.