rear drum brakes issue

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HemiDenny

HemiDenny

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needs some help, 8-3/4, rear drums, everything new.

the drums refuse to rotate when I tighten the wheel down. if I loose the lugs slightly, it will rotate, but when I tighten them down, movement / rotation stops. It does it on both sides the same with the wheel tire off (so it is not a tire rub). I have tried......

removing drums and re-adjusting the brakes

new, different drums

small spacer / shim between drum and axle flange

checked the backing plates...zero sign of contact with drum

checked the drum... zero sign of any contact with backing plate or anything else (brake shoes)

I'm stumped and looking for ideas.....all welcome.
 
Masking tape on shoes die marking blue on inside of drum install tighten turn slightly stop remove and look for witness mark.
 
Should look like this. 1 3/4" wide shoes, large shoe in the back (big girls in the back)

Screenshot_20230216-063309_Gallery.jpg


Factory Bell Drums

Screenshot_20230216-063343_Gallery.jpg


☆☆☆☆☆
 
You probably have too wide of a break Shoe in it, something other than what is supposed to be in there.

Do you have the wider B Body shoes in it, like 2 1/2" wide?

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George Jets said:
You probably have too wide of a break Shoe in it, something other than what is supposed to be in there.

Do you have the wider B Body shoes in it, like 2 1/2" wide?

☆☆☆☆☆
Click to expand...
that is / was my thinking, so I spaced the drum out with shims. no help but will take another look at it.

how wide should the shoes be?
 
HemiDenny said:
that is / was my thinking, so I spaced the drum out with shims. no help but will take another look at it.

how wide should the shoes be?
Click to expand...
depends on the brakes.... take off a drum measure the surface the shoes ride on.. most common is 2.5" then check the shoes
 
He said there was zero contact on the back plates but thats my guess also, or shoes too wide.
chalk,blue, paint or something to see where the contact is would be the next step imo.
Never heard of this problem before without it being obvious where the problem is.
Curious!
 
Lay a straight edge across the axle face and get an accurate as possible (depth gauge) reading to the highest point on the shoes edges. Then transfer that to the interior face of the drum. I bet the shoe edges are hitting. If that is no joy, measure from outermost edge of drum to inner drum face, then from axle face to backing plates If that is the problem, and they otherwise appear OK, it should be no problem for someone with a brake lathe to take some off the outer lip
 
I'd try putting on wheels with no drum. definately puts the blame on the drum that way. work backwards from there. You are much more experienced than I so.......just my $0.01
 
@HemiDenny

Let's start at the beginning....

  1. Is the 8 3/4 housing an unmolested A body housing?
  2. Are the backing plates A body backing plates?
  3. Are the axels unmolested A body axles?

Let's get some data before we all toss out answers.
 
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I would start with pulling the brake shoes and hard ware off one side . Install the drum and wheel if the problem is still there. Most likely drum to backing plate interference . If not probably the shoes.
 
The drum is probably locking down against the shoes that are too wide, or possibly locking down against the backing plates. My guess it's the shoes.
 
I bet it's the shoes. I see a lot of listings for 10 x 2 rear brakes these days, which I don't think really exist — people just don't know how to measure them. Factory A-body 8-3/4 rear drums were 10 x 1-3/4, and that dimension is the width of the shoe, not the depth of the drum. People get confused and measure the inside depth of the drum, which is closer to 2 inches, and wind up using front brake shoes. The shoe needs to be significantly narrower than the drum.
 
Photos are the only thing that will help ...................
 
Hopefully you checked the new parts against the old before you threw the old parts out. If you still have the old parts, just check the shoes and drums against each other.
 
HemiDenny said:
needs some help, 8-3/4, rear drums, everything new.

the drums refuse to rotate when I tighten the wheel down. if I loose the lugs slightly, it will rotate, but when I tighten them down, movement / rotation stops. It does it on both sides the same with the wheel tire off (so it is not a tire rub). I have tried......

removing drums and re-adjusting the brakes

new, different drums

small spacer / shim between drum and axle flange

checked the backing plates...zero sign of contact with drum

checked the drum... zero sign of any contact with backing plate or anything else (brake shoes)

I'm stumped and looking for ideas.....all welcome.
Click to expand...

Hey Denny, I ran into a similar problem when I replaced the side axles with Mosher's with a 4 1/2 " bolt circle. I was using a 741 housing with a cone style sure grip. Have you set the axle end play using the adjuster? . If you are using green bearings, the adjuster is not needed.What Sure grip are you using? Cone or Clutch style? Thrust button / Thrust spacer may be different depending on which unit you are using. I'm thinking you are locking up the differential by tightening the axles into the thrust button too much and stopping them from moving.
 
AAndrews said:
Thrust button / Thrust spacer may be different depending on which unit you are using. I'm thinking you are locking up the differential by tightening the axles into the thrust button too much and stopping them from moving
Click to expand...
Op said issue only happens with the wheels installed. That suggests the axles turn freely otherwise.
 
lots of good comments and things to look at.

I cannot answer some of the comments because I got the components in a stalled project....new axles with green bearings, complete rear drum brake package assembled with powder coated backing plates and new drums, 742 center section ready to bolt in all ready to be added to a stock OEM A-body 8-3/4.

I am suspecting the assembled drum brake package I used has incorrect shoes. Just miffed I cannot see anything rubbing.

As soon as I get a chance, I am gonna remove the shoes and see what happens.

Thanks for all that chimed in, much appreciated.
Denny
 
Shoe size, 1 3/4", can be measured in situ & is the first thing that should be checked, given the problem.
 
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