The Stovebolt Site Forums The Shop Area Engine Shop Brake adjustment 53 GMC 1/2 ton

I have a 53 GMC 9300 1/2 ton with the original brake system on it. Just put it on the road for the first time yesterday. The brakes seemed to be adjusted properly. The pedal was hard and it didn't move very much. After driving it for a few miles I noticed that there was starting to get a drag to the truck so I headed home. The brakes were kind locked up and hot when I got there. After sitting for a while and cooling down the wheels turn free again.

My questions are...
Should the rod on the master cylinder move in very much, cause mine doesn't?

When adjusting the star wheel on the drums, how much if ant drag should there be and which way do you turn to loosen and tighten ?

1. There should be a little free-play in the master cylinder rod.

2. The brake shoes should not be touching the drum after a proper adjustment. Usually, you adjust the shoes until they just touch the drum and then back off 5 clicks.

These procedures are described in the GMC Maintenance Manual (available from reproduction parts vendors on onl-line and on eBay).

#2 is at least part, if not all, of your problem.

Tim

Thanks for the reply Tim...I tried a couple of things yesterday. First I backed off all the adjusters as far as they would go. They moved freely so I assume they went all the way. Took it for a drive and same thing, in a couple of miles I could fee the drag and by the time I got home they were real tight.

I was reading in the shop manual about master cylinder cleaning so, I removed mine and took it apart. It was dirty inside and I noticed a few holes plugged. Also, at this point when I spun the wheels they all spun very freely. I thought I found the problem. I cleaned everything and unplugged the holes then installed the master cylinder and finished up by bleeding all the lines. Well, the drag was back on the tires that spun freely when the master cylinder was removed. I'm thinking that I might have some sort of master cylinder problem. Any ideas ?
Dave

Did the piston move freely in the master cylinder?

Do the three rubber hoses in the brake lines look OK?

Sounds like it is time to rebuild/replace the master cylinder and maybe the wheel cylinders.

Maybe someone else will post better advice.

Yes, the piston move freely in the cylinder.

I'm not sure what three rubber hoses you mean.

The wheel cylinders look good. No leaks or anything, and they return to the seated position when I removed the master cylinder.

http://www.classicparts.com/1947-59--Brake-Hose--1_2--3_4-Ton/productinfo/71%2D305/

Two on the front and one on the rear. Crawl under your truck and trace the brake lines from the master cylinder to the wheel cylinders. The two front hoses provide the flexibility for the front wheels to turn.

Oh okay....those are all new.
All the lines have been replaced on the truck.

You're out of my league, now (the bush and shade-tree league). Let's hope that someone else can provide a better diagnosis.

Thanks Tim

I have a gut fealing it's the master cylinder thats the problem. I think I will order a new one and see what happens they are not that expensive. I don't think the pressure is being released when pressure is taken off the brake peddle.

Dave

You didn't say weather you checked the push rod free play like TC sugested. Ithink it is not letting the piston come back all the way. There should be a small amount of free play in the pedal before it pushes on the cyl. Ther is an adjustment on the rod. Some use an eccentric bolt. You loosen the nut & turn the bolt to adjust it.