Rear Brake Problems

[Cheyenne Supr]

Hi all,
I have never had so much trouble with a set of rear brakes. I have a 69 C-10 with 6 lug wheels. I had a bad wheel cylinder on the driver's side so I replaced it and went ahead and changed the brakes and any worn springs as well. Although everything went together, and we have verified the parts are correct, the shoes just don't fit quite right when assembly was complete. There is about a 3/8" gap between the top of each shoe and the top center pin on the backplate (see pic with top springs off). Which makes the drum tight and the shoes are not against the backplate correctly (yes, the adjuster is adjusted all the way in). At first we thought the wheel cylinder links (push rods) that push the shoes out were too long, but I bought a new set at NAPA and they are correct (see pix). The rods are all the way into the cylinder. When I remove the rods from the wheel cylinder and assemble, everything fits together perfect. I'm considering grinding them shorter, but I'd really like to know what the problem is. I have a 3:73 rear end (HA code) with 6 lug wheels & coil springs. I'm wondering if maybe I need different wheel cylinders, but 60-73 seem to be the same. Perhaps I need C-20 cylinders? They are larger bore, but maybe shorter? This would mot be the first thing on this truck from a different year or model.
Any ideas?
Thanks for your help.
Larry

[Longhorn Man]

Have you compaired the cylindes to your old ones?
I am personally getting annoied at NAPA and there parts listings for these trucks. Here lately, I have had to send everything back and match up what I need by carrying it in.

[tcb-1]

I'm just guessing here, but the adjuster looks like it's way too short? you may trying to increase the length a bit and giving that a try.

my .02

[Cheyenne Supr]

Yes, I compared them and the cylinders appear to be correct. Still unsure about the rods though. Everything was in pretty bad shape when I pulled it apart, with leaky cylinder, some broken springs and lots of crud. So it was very difficult to tell how well all the old stuff fit together.
Larry

[Sammy]

I am going to take a stab @ the shoes. I would check make sure you have a short/ long not two longs or the shoe is wrong.??

[Cheyenne Supr]

Yes, I have a short with a long (short shoe in front).
Thanks.

[blaserman]

I had the sane problem with my 86 Blazer and it was the whell cylinders. The rods were to short and they had to look for longer ones. Again it was NAPA. Now I use AutoZone and have not had any problems with them.

Art

[Luvlegs]

I am by no means an expert but I'd try two things - I notice in the pics you don't have the upper springs on - Try to loosen up the bleeder on the cylinder, then push the shoes together, tighten up the bleeder and put the springs on. You might be trying to compress the cylinder but it has no "give".

You might also consider opening up the cylinder - perhaps they installed a double piston cap or two - I know that's a long shot but I didn't think mine would need grinding to fit either.

[70GMCer]

Those cylinder plungers are not seated all the way in. Keep in mind, it takes some hard pushing to get them in further. If they have been sitting on the store shelf for a long time, the lube they use might have dried up inside. Open the outer rubber sleeves and make sure the plunger cups are moving in and out without binding. Also, as you are pushing inward, open the bleeder.

[jayharrell]

agree... i replaced mine a couple of weeks ago. I pushed the plungers in before i installed it. That did the trick.

Also had to double check that the shoes were pushed all the way to the back of the housing, they flared out at the top and gave a bigger gap then needed.

[Wrenchbender Ret]

Where are the emergency brake parts? If the cables are adjusted up to tight or sticking they will cause this but I don.t see any.

[kxnomore]

I would guess those are the wrong shoes. I had the same problem with the brakes on an Eaton HO 52, and it took 3 tries at Napa to get the right ones.

The place where the pushrods for the brake cylinder slides into needs to be bigger. They should slide right in easily.

Did you keep the old shoes? if so, check them for the exact same dimensions. Mine were off just like yours.

Good luck.

[Cheyenne Supr]

Hey guys,
I found the problem and thought y'all might want to know what it was. All the parts I had were correct; shoes, wheel cylinders, push rods, springs, etc. I had already loosened up the cylinder bleed screw and pushed the rods all the way in, bled the lines, assembled and drove the vehicle, but the shoes locked up on the drum and would not release...I could barely get the drum off. I figured I had gunk in the brake lines and tried to vacuum bleed the system with 25 lbs of pressure, but I could barely draw any brake fluid so I knew something was wrong with my lines. At that point I began to take off lines one at a time and blow them out with 90 psi air pressure. What I found was the rubber brake hose at the passenger rear wheel had collapsed inside and was acting as sort of a check valve. It would let a very small amount of fluid out to the shoes, but nothing could return back through so the shoes would not release. The hose looked fine outside, but was almost completely plugged inside. With a new brake hose and clean steel brake lines it works like a charm!
Thanks for all your ideas. They did help me to brainstorm!
Larry

[jayharrell]

Good diagostics. Seems everytime i put a new part on mine it forces an older weaker one to go a head and fail also.

[68gmsee]

Originally Posted by Cheyenne Supr

..... I had already loosened up the cylinder bleed screw and pushed the rods all the way in, bled the lines, assembled and drove the vehicle, but the shoes locked up on the drum and would not release...I could barely get the drum off. I figured I had gunk in the brake lines and tried to vacuum bleed the system with 25 lbs of pressure, but I could barely draw any brake fluid so I knew something was wrong with my lines. At that point I began to take off lines one at a time and blow them out with 90 psi air pressure. What I found was the rubber brake hose at the passenger rear wheel had collapsed inside and was acting as sort of a check valve. It would let a very small amount of fluid out to the shoes, but nothing could return back through so the shoes would not release. The hose looked fine outside, but was almost completely plugged inside....
Larry

That's a fairly common problem and it has happened to me before. But the culprit, in my case, was the rubber brake hose that's on top of the rear axle.

What's confusing in your case, and the reason no one suggested the hoses, is that you had loosened the brake cylinder bleed screw. That should have easily seated the shoes...

[Cheyenne Supr]

Yes, mine was also the rubber brake hose on top of the axle at the passenger side rear wheel.

I think I probably had the shoes seated after initial assembly (or close to it, at least enough to get the drum on). Then they locked up after I drove it and would not release. It made it seem as though the push rods were too long but I was pretty sure that was not it. I didn't want to just open the bleed screw and try to seat the shoes, knowing they would lock up again because I hadn't determined root cause. That's when I began going through the lines and doing process of elimination.

Larry

[68gmsee]

That makes sense... It's the identical problem that happened to me many year ago. There was enough pressure with my power brakes to force the fluid towards the cylinder but no enough with the spring tension to reseat them.. Wasted a whole weekend trying to figure out what was happening.

Thanks for the update.