Well I'm back with the same brake problem, I thought I had the problem ironed out. The wheel cylinders on the right rear wheel were sticking and not releasing (New cylinders) I ran a hone through them for a long time and findly got them to release. Anyway, I put it all back together and they seemed to work. I took a few test drives and all seemed fine, until yesterday when they locked up again.
Just a recap of all thats been done to the system.
New master Cylinder
New front shoes
Rebuilt front wheel cylinders
New front rubber and steel brake lines
New multi-vac/hydrovac
New rear wheel cylinders on right side (was having problems with them and found one to be rust pits. so I replaced it)
New rear brake lines rubber and steel.
Rear shoes and drums are in very good condition.
There is not a proportioning valve
My question is, if the right rear brake was ajusted closer to the drum than the left side could the right side lock up and not the left side. And if so, could the problem be in the vac system even though its new? If this was the case wouldn't I see the problem at other wheels. How would you test the multi-vac for this and what could cause this?

 

If it is a problem with only one wheel then you can forget about the master cylinder or the booster system.
As for shoe adjustment then if the brakes were not adjusted equally one may lock up before the other but both will release when the pedal is released.
If the brake is dragging (not releasing after pedal is released) I would again at the wheel cylinders, the ones you are getting seem to be junk. Also make sure that the shoe retraction springs are good.

 

Thanks lazy K, I did forget to mention that I had replaced the springs on that wheel (sorry). Do you have any idea how thight the wheel cylinders should be. When I checked the cylinders it took a fair amount of presure to get the cups to return, what I mean is, I was pushing from one side of the cylinder to the other and the spring would collapse before it would push through to the other side. so I honed the cylinders until they would return but with some resistance.
thanks again for gettin back to me

 

I would not be worried about the resistance in the wheel cyl pistons that you describe, the shoe retraction springs should handle that OK.
I would be more concerned, with the wheel cylinders in place and connected to the brake line, how hard is it to press both pistons in simultaneously? I`m still thinking a restriction in the brake line.
I can`t remember from the last post but have you checked that the drum is true, the backing plate is true, the wheel bearing is good and that the primary and secondary shoes are the correct way round?

 

The backing plate has been reworked, I have not checked the drum for roundness although I feel or hear didn't it rubbing against just one shoe or fell any hard or dragging while it was free. I guess I could check it with a dial indicator. Wheel bearing and seals are new all but the left rear.
I'm not a mechanic although I've done alot of automotive work over the years and always thought I did pretty good work. Never thought I would of got in this kind of a mess with something as simple as brakes..............

 

Oh yea, forgot to ask you a stupid question?? to me the shoes look like mirror images of each other. I've seen that before so I looked at them closely and didn't see any deference. Is there a way of telling them apart and which one goes foreward

 

I 2nd that

 

The primary shoe (faces the front of the truck) should have a shorter lining on it than the secondary shoe (faces toward the rear of the truck).
The shoes themselves can look exactly the same but the length of the friction lining fixed to each can be around an inch different.

 

Hey does anyone know how I mite check for the correct push rod length. I never checked that when I installed it. Seems to have about and inch of travel before the brakes start to engage. Its going to rain all weekend so I'll go at it again.......................

 

just wanted to keep this going, still looking for possible answers. have not found the problem yet...............

 

I was just crawling around under the truck and scratching my head when I saw something that may be a check valve. I’m getting tired of just guessing and having to re-bleed the system not to mention that the wheels and drums are just a little on the heavy side. Coming from the frame mounted multi-vac there is a line at the end of what I would call the slave cylinder, it goes to a junction block and from there the lines separate, two to the front brakes one to and rear brakes and the is also the brake light switch all on this block. Anyway where the line from the vac goes into this block at the frame ( its hard to see because it goes through the frame rail) there is a round fitting going into the distribution block. Anybody have any idea if this mite be a check valve. Several times folks here have mentioned check valves. Would check valve be built into the master cylinder or the Multi –vac???

 

don`t know what that is but if it was a problem I would think it would cause both rear brakes to lock up, not just one.

 

I was just wondering if the brakes were not all adjusted to the correct adjustment, and the right rear brake was adjusted closer to the drum, would it not grab first. And if there was a problem else where in the system would that brake stay maybe locked?????
A few folks had mentioned that there could be a check valve causing the problem. So I did some reading and the service manual said that if there is a frame mounted booster that is where the check valve should be. And when I was looking at the re-build procedures for the master cylinder it showed a check valve behind the piston. Should this be removed?? As I stated earlier the master cylinder was one of the first things I purchased for the truck and maybe there is a check valve in it. If you go to the local auto parts store they would just sale you what’s on the shelf…. I’m just guessing, anybody have any thoughts??????? <!-- / message -->