4" to 4.5" Bolt Pattern on a 7 1/4" Rear?

shhnappa said

Thanks, but want to clarify one thing. If I were to get a 73, 74, 75, 76 Dart/Duster (basically any A-Body) 7 1/4 rear axle shafts, I could just replace my existing SBP axles with no modifications at all, except replacing the drums? I mean, the spline number & diameter are identical?

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No. DGC said those years AND disk brakes are BBP rear. I have a 73 with drums all around and it is a SBP car. I used a 75 rear on the Demon and it has BBP. However, I do not know what brakes were on the donor car. Somewhere in the archives, I have read that all of the 75-76 models were BBP cars, but I can't confirm.

Since the 8 3/4 was an option on all cars, you may already have one. If the rear cover is smooth, bingo. My recommendation at that point is to buy a pair of A-body BBP axle shafts and drums to match the ones removed, save the bolt pattern, and live happily ever after.

If the rear cover of the axle has 10 screws and a 1½ inch axle tube is is a 7¼. If 10 screws and a 3 inch axle tube it is an 8¼ axles.

Another possibility is that you have or find a Sure Grip differential. With the wheels off the ground, twist a wheel counterclock wise. If the opposite wheel spins the same way, you have Sure Grip. If the opposite wheel spins in the opposite direction, you have an open rear end.