Rear brake Lock-up 70 C30

[CCCC]

Went out this AM to move the tow truck from the storage garage for some carb work and found that one rear wheel is almost locked (dually). The truck will move backward with some strain but will not push forward. Low fluid level in the rear bowl on the master cyl tells me there must be a leak and it's probably at that wheel - although no exterior evidence.

Would such a leak cause the brake shoes to swell enough to lock up on the drum?

Numerous "pumps" of the pedal after filling the MC does not seem to have helped break it loose and, in that the other rear wheel spins OK, it seems like this is not a rear hydraulic lock-up. While I'm preparing to drag the truck into a workspace and tear into it, have you encountered such a surprise? And, what was wrong?

[demian5]

Pull the drum and all of your questions will be answered....

[El Dorado Jim]

not sure why, but i'm curious about what you are going to find out...

[CCCC]

Yes, demian, I agree. Just looking for some wise insights from someone who may have experienced this "all of a sudden" lockup.

With this rear it's 8 bolts, remove the axle; unscrew outer nut from spindle, remove locking/tab ring; unscrew inner adjusting nut; remove hub (probably tight and requiring some leverage) and survey the mess - probably a leaking wheel brake cylinder. Hub seal may be shot too,

Maybe the cyl could be honed and fixed with a kit - maybe needs a new cyl. Shoes probably soaked and beyond recovery, etc.

I've had them start leaking visibly and fixed them before they got bad - but never had one lock up while sitting,

[special-K]

If the drum is froze up taking it off will not be easy. I'd try to use the truck's power to break it loose, or drag it. I've experience this before and not sure if it's swelling or not. I think it could be rust.. With full-floaters, if an axle seal leaks the brakes will grab when used and get stuck when parked, so I think the brake fluid is doing the same thing

[demian5]

Originally Posted by CCCC

Yes, demian, I agree. Just looking for some wise insights from someone who may have experienced this "all of a sudden" lockup.

I had a 73 3/4 ton Suburban that would do that. I don't recall why but I do remember it was the opposite wheel that was locking up with the issue.

[CCCC]

Thanks guys. I was able to use truck power to back it out of one garage (reluctantly - with some opposite wheel spinning on gravel floor) and turned it to head out but then it would NOT move forward with truck power. So, dragged it forward enough to re-turn, and then was able to back it into the repair garage under power. Deplore it when this kind of thing happens - a negative product of enjoying so many nice old Chev/GM trucks but not running each of them as frequently as I should. Had a poor health spell for about 12 months and things got behind - this nice old tow truck sat in one place too long - and so here it is.

Am hoping that backing it freed to drum enough that I won't need extreme force to get the hub off there. Definitely will replace the axle seal even if not leaking there. Hope the wheel cylinder is not pitted - low moisture area here, so there is hope. Won't be able to dismantle until next week or so. May have more ?? then.

Thanks again.

[demian5]

It could be worn backing plates that nobody ever lubed, but with fluid loss as well, you will figure out your problem quickly.

[cleszkie]

What condition are your rear rubber brake lines in?. Although not common, the inner rubber surface of old rubber brake hoses have been known to delaminate. A flap of delaminated rubber can block flow either to or from the master cylinder. If it blocks flow back to the master cylinder, pressure will be maintained in the wheel cylinder and the brake will not release. This may also account for the low fluid level in the master reservoir if the fluid is being held in the wheel cylinder. Just a thought.

[Wrenchbender Ret]

These are all good possibilities to look for. Also check the emergency brake cable. A sticking cable can cause the brake to hang up. You will probably have to back the adjustment off to get the drum off.

[special-K]

I wondered about the brake hoe, but there is just one in the rear and one wheel turns. It could be delamination with a piece migrated to one side brake line. But how would that happen from sitting? He hasn't had the need to hit his brakes since sitting, I'd imagine. The brakes are on already.

My '71 wrecker had one side lock up and I shocked it loose. Same issue, sat too much which is why I decided to sell. It still had original ignition that I had all tuned up with new quality parts. But after sitting it just cranked. I figured condensation in cap/carbon tracks so I cleaned up/dried up with Lectra-Motive. Still wouldn't start. Turns out points were corroded bad, ready to be changed. I got under 50 miles out of that tune-up, and the brakes had just been done when I bought the truck. Too bad you don't have some pavement for that wheel.

[CCCC]

Good stuff guys - thanks. I sure will check any rubber line components - have spares here - and will make sure the lines are clear. Yes, will probably have to back way off on the adjuster to get that hub/drum off. S-k - the floor in this one garage is concrete and I'm going to try some pushing/rocking before I proceed further - just don't want to scorch anything while trying.

Busy weekend now through Sunday - will not get back to this brake issue until Monday. Will posta again once it's open/diagnosed.

Thanks again.