moparmark65
Well-Known Member
I have a 69 dart gts that has a 7 1/4” rear end. I have found a ‘70 8 3/4” for B body. What will I need to do to make this fit properly?? Thanks for the input!
Swapping rear end question.
- Thread starter moparmark65
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Professor Fate
Push the button, Max...
A '69 GTS should have an 8.75, so I'll assume the 7.25 was swapped in or is just there to make it a roller...
Read this post carefully: An accurate 8 3/4" rear axle width list
A factory A body 8.75 housing is 52 5/8" wide. A '70 B body housing is 54 15/16" (let's call it 55 here for simplicity's sake).
That means the B body unit is 2 3/8 wider than an A body diff, or 1 3/16" per side.
B body brakes are wider than A body units, which increases the difference to about 3" overall, or 1.5" per side. This will all have to be made up for with wheel offset, especially in the confines of a Dart's rear wheel opening. The other option is to have the housing narrowed to A body specs.
As far as getting it mounted, the spring perches will need to get cut off and new ones welded on at the correct A body dimension, and keeping the pinion angle within spec. The 7.25 U bolts and shock plates are for 2.5" axle tubes, and the 8.75 has 3" tubes, so those will need to be replaced with the proper ones.
The driveshaft for a 8.75 is *about* an inch shorter than one for a 7.25.
The axles for a B body rear have a 5x4.5" bolt circle, all pre-'73 A bodies have a 5x4" bolt circle, which means your front and rear bolt circles (and wheels) will be different.
Read this post carefully: An accurate 8 3/4" rear axle width list
A factory A body 8.75 housing is 52 5/8" wide. A '70 B body housing is 54 15/16" (let's call it 55 here for simplicity's sake).
That means the B body unit is 2 3/8 wider than an A body diff, or 1 3/16" per side.
B body brakes are wider than A body units, which increases the difference to about 3" overall, or 1.5" per side. This will all have to be made up for with wheel offset, especially in the confines of a Dart's rear wheel opening. The other option is to have the housing narrowed to A body specs.
As far as getting it mounted, the spring perches will need to get cut off and new ones welded on at the correct A body dimension, and keeping the pinion angle within spec. The 7.25 U bolts and shock plates are for 2.5" axle tubes, and the 8.75 has 3" tubes, so those will need to be replaced with the proper ones.
The driveshaft for a 8.75 is *about* an inch shorter than one for a 7.25.
The axles for a B body rear have a 5x4.5" bolt circle, all pre-'73 A bodies have a 5x4" bolt circle, which means your front and rear bolt circles (and wheels) will be different.
HemiSSDart
Dartus Interuptus
The only B-Body rear that is almost a swap for an A-Body is a 65-67 unit and the spring perches are only 1/2" wider than and A-Body. I have done this swap a couple of times, it is pretty much a bolt in and the rear hangars can make up for the 1/2" difference. The biggest issue on a Dart is that the wheels will have to be made or found for the correct backspacing to bring the tire in closer to the frame rails, I had a set made. On a 65-69 Barracuda and a Duster/Demom it is much easier to find wheels as they wheel wells do not shroud the tire nearly as much as a Dart...
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