Rear Drum Brake Issue

[saskman02]

My 67 C-10 was converted over by the PO to a 1978 5-lug front disc / rear drum setup. The issue I am having is only the top of the rear brake shoes are contacting the drum, the bottom 2" - 3" of the shoes look like they just came out of the box. I took it out to a gravel road and all the braking is being done by the front discs, I could not get the rears to lock up. The truck was fully restored 5 years ago and when I pulled the drum off for the first time there was little to no brake dust telling me the brakes have never worked properly since the restoration. All components appear to be have been replaced 5 years ago. I bled the rears and no air was present in the lines. Also turned out the self adjuster until the shoes were just starting to contact the drums and still the bottoms won't bite when braking. The drums measure 11 5/32" and the shoes are 2 3/4" wide. The booster & master cylinder are both new. The proportioning valve is rusty so it looks like it came off the 78. As shown in the picture below, the portion on the shoes that are contacting are a slightly different color than the portions that aren't. I wish I had measured the difference in thickness of the shoe from the top to the bottom but I forgot. Both sides have the same problem and are wearing almost exactly the same. Any ideas as to why the bottom of the shoes aren't biting??

[nonstop]

Are the self adjusters mounted on the correct sides?

[saskman02]

Originally Posted by nonstop

Are the self adjusters mounted on the correct sides?

Not sure...What determines if they are on the correct side? The pic above is of the drivers side.

[nonstop]

Originally Posted by saskman02

Not sure...What determines if they are on the correct side? The pic above is of the drivers side.

Easiest way to check is when you push the lever down (multiple times to actually see movement), the shoes should expand out. Other thing to check is if backing plate is grooved.

[friscobob]

Sounds like part of the proportioning valve has gone overcenter, a safety (?) device to isolate front from backs in case of a leak or other failure.. I had the same problem on a 67 I used to own, it had 71 brakes installed on it. i have no idea how to recenter that valve, there is a tool one can buy that screws in place of the brake failure light switch that prevents the valve from closing. Hope this helps. I think your rear shoes will center themselves when you get pressure to them.
Bob

[saskman02]

Originally Posted by nonstop

Easiest way to check is when you push the lever down (multiple times to actually see movement), the shoes should expand out. Other thing to check is if backing plate is grooved.

Yes, I have adjusted the shoes out by pushing the lever down. Went to far (couldn't get the drum back on) and went a couple clicks up and it fit snug.

Originally Posted by friscobob

Sounds like part of the proportioning valve has gone overcenter, a safety (?) device to isolate front from backs in case of a leak or other failure.. I had the same problem on a 67 I used to own, it had 71 brakes installed on it. i have no idea how to recenter that valve, there is a tool one can buy that screws in place of the brake failure light switch that prevents the valve from closing. Hope this helps. I think your rear shoes will center themselves when you get pressure to them.
Bob

I half suspected the proportioning valve but wanted to confirm the brake was assembled properly before going down that road. Will probably just start with a new valve and go from there.

[chrismoore701]

I could be wrong. But if I recall the larger of the two shoes goes on the front. If this is the driver side it is backwards

[Shady Rascal]

Originally Posted by chrismoore701

I could be wrong. But if I recall the larger of the two shoes goes on the front. If this is the driver side it is backwards

You've got it backwards. Shorter shoe goes on the front.

[GRX]

Originally Posted by nonstop

Are the self adjusters mounted on the correct sides?

Originally Posted by saskman02

Not sure...What determines if they are on the correct side? The pic above is of the drivers side.

Threads. One with left-hand thread goes on passenger side. Right-hand thread on the driver side. That way when the lever pushes down on the star wheel it will unscrew it.