Converting rear drum brakes from SBP to BBP
Please let me know if my research is correct for the rear end. To install a 8 3/4 my options are:
Find a 8 3/4 from a 65-72 A body then change the axle shafts to BBP and either drill the drums or change backing plates and drums from BBP car.
Find a 62-70 B body rear end and move the spring perch in 1/2" which will require new perch with 1/2" locating pin hole.
Are these my options?
Um, sort of.
Yes, a 65-72 A-body 8 3/4 should bolt right in. If you change to BBP axle shafts (with the BBP flange offset) then you
must change to BBP backing places and drums. If you have the stock SBP axles drilled for the larger bolt pattern (or you buy Moser axles with the SBP flange offset), you have to drill the SBP brake drums for the larger bolt pattern and use the re-drilled SBP brakes. You can't mix and match parts between BBP and SBP brakes and axles, has to be either all BBP or all SBP, even if the SBP stuff is drilled for the 5x4.5" pattern.
The 62-70 B body axle thing- first, I know
exactly what chart you're looking at if you say 62-70 B-body 8 3/4, and that chart is totally wrong. Completely wrong. Use this chart
An accurate 8 3/4" rear axle width list
There are literally 4 different width B-body rear axles from 62-70, and anything before '65 has a tapered axle set up that you do NOT want. So, you have two real options that don't involve major pain, both will need the spring perches moved to the A-body perch width.
65-67 B-body 8 3/4 = 59.5" drum to drum
68-70 B-body 8 3/4 = 60.125" drum to drum
So, you can see these are wider than an A-body 8 3/4. If you move the perches the axles will bolt right in, and you'll have BBP brakes, but you will need rims that have more backspacing than a stock A-body. Especially you use the 68-70 B-body 8 3/4, you may have a hard time finding 15" rims with enough backspace to run wider tires. If you want to run 17" or 18" wheels, no problem. In fact, the wider rear axle will be beneficial, because there are a lot of off the shelf 17 and 18" rims with enough backspace, especially for a Barracuda. But if you want to run 14" or 15" rims and anything wider than a 225/60/15, you will have limited options for 15" rims, and almost no options for 14" rims, unless you have them custom made.
For example, I have a 68-70 B body rear in my Duster. I did a 1/2" spring offset when I installed it (have to move the perches anyway, might as well), and I run 18x10" rims with 7" of backspace (+38mm offset). But before I bought those rims, I ran the car with 15x7" cop wheels with a 4.25" backspace and 225/60/15's. They
barely cleared the quarter panels. And finding significantly positive offset 15" rims isn't that easy. So, you may not want to use a B-body 8 3/4 if you plan on staying with 15" stock style rims.
