8.75 Rear End Drum Brakes

dewsky · May 22, 2018

Ok guys....here's what I have. I did not do the work, so I am trying to figure this out. Believe it was an early Barracuda that donated it's 8.75 rear for my 1975 Duster. Rear end has upgraded axles to go to the BBP. When I pulled the rear wheels off, I found a wheel spacer between the axle and the brake drum. I asked the guy who I bought the car from and he said the shop he took it to put them on that way because the drums were rubbing on something. I believe that they got the BBP drums, but did not change the backing plates for the brakes. Does this sound right to you guys? I know that if I remove the spacers, the drums hit so hard they almost lock the axles up. I was thinking it was only the drums since there are two different ones but the backing plate could be the real culprit. Is there a way to tell? I am really thinking that I should just convert the rear to Disc's and eliminate this headache.

65Val · May 22, 2018

This might help...
8 3/4 brake backing plates A vs B | Moparts Question and Answer | Moparts Forums

MoparMike1974 · May 22, 2018

Wrong drums for the backing plates. Measure the width of the brake surface inside the drum.

72bluNblu · May 23, 2018

Sounds like you have a mismatch between your axles and your brakes. SBP axles have a different flange offset than BBP axles-

And what that means is that the backing plates also have different offsets. So, the backing plate for a 10x1.75" SBP drum brake set up can not be used with BBP axles, you have to use a backing plate for a 10x2.5" drum set up. No mixing and matching of axles and backing plates.

To measure the backing plate offset you want to set the backing plate flat on a bench. You'll need to hang the bottom 1/3 of the backing plate off the edge of the bench so that the mounts for the e-brake cables don't keep the backing plate from sitting flat. It isn't much, but they do change the measurement. Then, measure from the bench to the top of the backing plate through the center hole (for the axle) in the backing plate.

BBP plates will measure ~1.75", the SBP 10" backing plates will measure roughly 1.25"

Checking the drum or shoes won't help, you can put 10x2.5" shoes on a 10" SBP backing plate, you just end up with interference when you install the drum.

For extra fun, you can buy brand new aftermarket axles that have the 5x4.5" bolt pattern, but the SBP axle flange offset. Those have to be used with re-drilled SBP drums.

Frnknsteen · May 23, 2018

72bluNblu said:
Sounds like you have a mismatch between your axles and your brakes. SBP axles have a different flange offset than BBP axles-

Yep,... What Blu said. Seems to me, when I talked to Cass at Doctor Diff about changing my '67 Barracuda to big bolt pattern, he told me the same thing and said I'd have to get new brakes because of the axle sticking out further. They sell a 10x2 1/2 brake assembly there (for $350) that comes with the backing plates, drums, and all the hardware. I just checked though and it is showing out of stock. Might check with them and see when they expect them to be back in stock

Daves69 · May 23, 2018

72bluNblu said:
.........For extra fun, you can buy brand new aftermarket axles that have the 5x4.5" bolt pattern, but the SBP axle flange offset. Those have to be used with re-drilled SBP drums.

Lol, drums are a piece of cake...……