My son and I will probably convert his 70 Duster to discs this winter. He has the factory 8.75 rear end and this is going to involve purchasing some big bolt pattern axles from Dr. Diff.

I haven't looked into everything completely, but I understand that the A body 10" rear drums have a 1.75" brake shoe and the big bolt pattern axles will need 2.5" shoes. This will require different backing plates.

The question is this. Which brake backing plates can I use for the bigger shoes? B,C or E body 10" drums and backing plates? Any of those or all of those.

Thanks

Any one other than the A body SBP ones will work. You can also us FMJ and R bodies as donors. I had a set of M body cop 11" drums on my 8 3/4 for awhile. I believe Doc Diff sells a drum brake kit all ready to go and all new. Might save on shipping if you go that route when you get the axles.

Thanks for the reply. He does have an entire assembly ready to go for $475. It's going to boil down to what it will cost to piece everything together vs using his out of the box parts.

Thanks

When it comes to brakes, the backing plate and maybe the drums is all I'd think about using used. But find them around here anymore is tough.

Don't forget that any BBP pass car axle can be the donor, not just an 8 3/4. I sort of priced out the 10" setup at Rockauto, sans backing plates and using Bendix or Raybestos parts, about $170.

Two things you can do on converting the early A body small 4.0 bolt pattern axles to the 4.5 bolt pattern, you can have your axles drilled for the 4.5 pattern and use screw in studs or buy new 30 spline axles for the stock A body housing axles and stock 1 3/4 size brakes and have the O.D. of the axle outer mounting flange cut down to clear the stock 1 3/4 brakes drums and use the stock parts or buy a set of 10.0,10.5 or 11.0 backing plates and drums and used them with the new axles set up for the standard B,C and E body 8 3/4 rear ends
Your choice

If a person bolts on the bigger brakes onto the existing A-body housing, and buys new axles instead
of redrilling the old axles, aren't the new axles longer by about 3/4-in ?
If you don't narrow the housing, the bigger brakes are wider so you need longer axle shafts, or so I thought.

Yes, you are correct. The Doc Diff BBP axles are setup for the swap he's doing. Some other people like to muddy waters I guess.

I just did this on my 72 Duster If you want to change the bolt pattern you have 2 options buy new axles which have the BCE axle offset and use the BCE rear drums and backing plates or you can redrilll your A body axles use the BCE backing plates and the "front 10 inch drum" It works out perfectly. I had all these parts sitting around it cost me nothing and works great.

All good stuff guys. The plan is to get Dr. Diff axles and use the BCE backing plates and drums. There are a couple of guys locally that I can get the backing plates from and the drums run about $50.

I was lucky when my mom gave me her 1974 Dart Swinger after the electrical fire. It was a /6 auto but had LBP all around.
The rear end was a 7 1/4 open but had 10 X 2 1/2 drums. I ran that rear end when I took my Ford 9 inch out of my 65 Barracuda. One day it went BANG and was making a grinding noise like bearings so that is when I swapped my 8 1/4 Aspin rear in. The Aspin rear drums were 10 x 1.75. I then took the drums off my 7 1/4 to find the grinding noise was just the left shoe lining had come unbound. I had the 8 1/4 in the car so I just went ahead and put the big brakes on that axle, Backing plates and drums with new 'Leroy' kit and shoes.