11" Backing plates rubbing
I run 11" backing plates on all of my cars, A-bodies included. I don't run smaller wheel cylinders and I don't have the rear brakes dialed back with an adjustable prop valve, and yet my cars are quite well balanced as they're set up. Yes, from the factory the 10" rear brakes had too much bias, but that was with factory crap-tastic bias ply's. Start running more tire out back and that's no longer the case. Upgrade your front brakes and that's no longer the case. Most folks run much larger/wider tires out back than they do up front, and that extra tire means extra grip and extra weight, so larger brakes may be very useful. The 11" drums work VERY well with an upgrade to 11.75" front rotors. It's not as simple as the 11" brakes are pointless extra weight, with the right combination of front brakes, tires, and suspension they can add some much needed braking improvements.
As for the drums rubbing on your backing plates, you likely have mismatched drums and backing plates. Remember that 11" rear drums came in 11x2, 11x2.5, and 11x3" varieties, and you can't swap drums and backing plates between the different varieties. Since the BBP axle offset was the same for all of them, the axle flange is in the same place for all of those and therefore the offset for the backing plates on each of the 11" drum set ups was different. Meaning, if you have 11x2" backing plates, you can't just buy 11x2.5" drums and shoes and run those. You're going to need to measure the backing plate offset to figure out what brakes you need to have for those 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.
If you get ~1.75", you have 11x2.5" plates. If you get ~1.5", you have 11x2" plates. Those I know for sure, as I've measured them. I don't have a set of 11x3" backing plates, but the math would say you'd get ~2" measuring them as I described above. This is because half of the additional width is on the inside of the axle flange and the other half is on the outside to keep the axle flange in the same spot, as there was only one axle offset for BBP 8 3/4 axles.
I run 11" backing plates on all of my cars, A-bodies included. I don't run smaller wheel cylinders and I don't have the rear brakes dialed back with an adjustable prop valve, and yet my cars are quite well balanced as they're set up. Yes, from the factory the 10" rear brakes had too much bias, but that was with factory crap-tastic bias ply's. Start running more tire out back and that's no longer the case. Upgrade your front brakes and that's no longer the case. Most folks run much larger/wider tires out back than they do up front, and that extra tire means extra grip and extra weight, so larger brakes may be very useful. The 11" drums work VERY well with an upgrade to 11.75" front rotors. It's not as simple as the 11" brakes are pointless extra weight, with the right combination of front brakes, tires, and suspension they can add some much needed braking improvements.
As for the drums rubbing on your backing plates, you likely have mismatched drums and backing plates. Remember that 11" rear drums came in 11x2, 11x2.5, and 11x3" varieties, and you can't swap drums and backing plates between the different varieties. Since the BBP axle offset was the same for all of them, the axle flange is in the same place for all of those and therefore the offset for the backing plates on each of the 11" drum set ups was different. Meaning, if you have 11x2" backing plates, you can't just buy 11x2.5" drums and shoes and run those. You're going to need to measure the backing plate offset to figure out what brakes you need to have for those 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.
If you get ~1.75", you have 11x2.5" plates. If you get ~1.5", you have 11x2" plates. Those I know for sure, as I've measured them. I don't have a set of 11x3" backing plates, but the math would say you'd get ~2" measuring them as I described above. This is because half of the additional width is on the inside of the axle flange and the other half is on the outside to keep the axle flange in the same spot, as there was only one axle offset for BBP 8 3/4 axles.
