B body 8 3/4 in Demon
Its all stock
relocated spring perch
I think its from a 69 b body
Nigel at Moparts told be it was 1 inch narrower than a stock a body rear end
Uh,
NO. The A-body 8 3/4 is
3" narrower than the B body 8 3/4 (if it's a 68-70 b-body).
The stock SBP A-body rear is 57 1/8" drum to drum (52 5/8 flange to flange). Spring perches are at 43" c-c (stock)
The stock BBP 68-70 B body rear is 60 1/8" drum to drum (54 15/16" flange to flange). Spring perches are at 44" c-c (stock)
As for people having solved this swap, yes, they have. :D I have a 68-70 B body rear in my Duster. Mine is not stock, my perches are at 42" c-c (1/2" offset) and I trimmed the outer quarter lip by roughly a 1/2" as well. I run 295/35/18's on 18x10" rims with a 7" backspace (38mm offset). If your spring perches are the stock A-body 43" c-c, and you haven't done any trimming or rolling on the quarter lip, the widest tire you're going to be able to safely run is a 275mm wide tire. But that should be a fairly safe option with a decent amount of clearance. I had 275's on my Duster without any modifications with no issues whatsoever.
As far as the backspacing, it will depend on what width rim you want to use. If you're looking for a 15" diameter rim you can go with a 15x8 or 15x9, either will work.
Assuming you really do have a B-body 8 3/4 out of a '69, and it's decently well centered with the perches moved to 43" c-c (stock A-body):
-For an 8" wide rim you'd want ~6" of backspace, and no less than ~5.75"
-For a 9" wide rim you'd want ~6.5" of backspace, no less than ~6.25".
If you're planning on a 17 or 18" diameter rim you'd need to use the 9" wide rim, the shorter tire sidewalls need the wider rim. You could even use a 9.5" wide rim, then you'd want ~6.75" of backspace, and no less than 6.5".
Not all of these cars are identical, the axles aren't all perfectly centered and the body's aren't all perfectly symmetrical, so it's obviously best to measure
your car and see what you've got. As already mentioned, it's better to go with a little more backspace than a little less, if you have too much you can add a small spacer. If you don't have enough, well, your only recourse is to trim the quarters or buy new rims.
