B-Body Axle?

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DesertRat

DesertRat

Leading edge boomer
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Tried searching. It appears my ready-to-go 8 1/4 rear axle is a B-body unit. The spring perches will work fine for mounting but the backing plate to backing plate dimension is 2" +_ narrower than the old 7 1/4 unit I removed. Anyone have experience with this and will it work? TIA-------:coffee2:
 
Narrower?

B body perches should be 44" on center. That's an inch too wide, you'll have to pull your springs in. Not a good idea IMO.
 
What car are you putting this in? Even the narrowest B-body rear is about 1-1/2" wider than a A-body rear if I remember right. And as Bruce pointed out the perches should be on 44" centers, not 43" like an A-body and I totally agree that it's not a good idea to spread springs to make them go in. You put the bushings in a bind when doing that and they won't last nearly as long as they should
 
Yeah, I'm not familiar with the 8 1/4 measurements, but the B body is a wider car than the A. It wouldn't make sense if it had a narrower rear than the A.
 
It appears I may have been wrong again. My casting # is 3723599 which is definitley a 8 1/4 axle but from my research could be an A-body unit. The dimensions are correct for post-72 A-body 8 1/4. Just trying to identify the brake shoes it needs as the first set I bought are incorrect and to have NAPA order the correct ones I have to identify the year-make-model of the brake shoes i need. Thanks all for the input!:coffee2:
 
Well, an A body rear is 52 5/8 flange to flange. That will give you an idea.

According to the chart I just looked at, it says 71-74 B body for that number you posted.
 
I know Bad Sport. I discovered the same but my spring perches are 43" and one chart I looked said they made some 8 1/4 A-body setups. By my measurements, everything should fit but time will tell. Now I am just trying to find the correct brake shoes for the unit!
DR:coffee2:
 
They made a LOT of a-body 8 1/4 rear ends.
The brakes are 10''X 2 1/2''.
Just order ones for a '73 and up 340 or 360 Dart Sport or Duster.
They put them in a lot of other V8 cars, but it might confuse the parts man........
 
DesertRat said:
I know Bad Sport. I discovered the same but my spring perches are 43" and one chart I looked said they made some 8 1/4 A-body setups. By my measurements, everything should fit but time will tell. Now I am just trying to find the correct brake shoes for the unit!
DR
Click to expand...

Dartnut is correct, and by your measurements it sounds A body to me.

Just go to a GOOD parts store, not one of the big box stores, and a good parts guy should have no trouble getting you the right ones.

When I put my B body rear in, I had no idea what it came out of, my parts guy is sharp as a tack and had no trouble getting it right the first time.
 
Thanks guys, went to NAPA this morning with all my info and got the correct shoes coming for pickup tomorrow. Counter man crossed my info to a 76 Dart with 10" X 2 1/2" shoes. Feeling better about it all since I had the thing completely rebuilt by Randys Ring & Pinion. Will post photos on my build thread when it is in!
DR:coffee2:
 
I have a 72 dart 7 1/4 rear and want to use a 66 charger 83/4 I can move spring perches and what ever else needs to be done without narrowing the rear. has anyone done this swap? and if so what did you do for rims and tires? it will be about1 3/8" wider per side
 
I can't say if this would be a good choice or not. I can tell you that my rear axle turned out to be an "A" body rear axle despite the casting numbers. I can share this with you. You will need the larger u-bolts and shock mount plates as the axle tube will be larger and the 7 1/4 stuff won't work. Also, be sure to keep the stock e-brake cables to retro into whatever you choose to put in the car. On the surface, you could probably move the spring perches and make it work with the correct offset wheels but unless the charger rear axle is free, I would probably try to find an "A" body axle. The change is hard enough if everything is right!
Good Luck with whatever you decide, DR:coffee2:
 
mopops said:
I have a 72 dart 7 1/4 rear and want to use a 66 charger 83/4 I can move spring perches and what ever else needs to be done without narrowing the rear. has anyone done this swap? and if so what did you do for rims and tires? it will be about1 3/8" wider per side
Click to expand...

The '66 Charger 8 3/4 rear should be 1-3/16" wider per side, that accounts for the width of the axle and the wider BBP brakes.

You shouldn't have any issues moving the perches in and using that axle. All it means is that you'll need to add more backspace to the rims you use, to the tune of 1-3/16". So, instead of a 15x8 with 4.5" of backspace, you'll need about 5.7" to 6" backspace. If you wanted to use 17 or 18" rims, it would be a piece of cake, because you could use Mustang rims. 17x8 with 5.72" backspace, and that would work in the front too. So really, for the larger rims, the 65-67 B rear is ideal, because it matches the front and rear backspacing.

It would be even less of an issue if you had a Barracuda or Duster, I run a 68-70 B body rear in my Duster, which is a whole 1.5" wider per side, but it has a lot more room to the quarters than a Dart.

Since you're moving the perches anyway, grab a set of offset hangers/shackles from Dr. Diff. Moves the springs in a 1/2" so you can run more tire, should be able to get up to a 275 with that offset. :D
 
I have a 69 Barracuda with a 7 1/4" differential and am eager to upgrade, to 8 3/4" if possible but also am considering 8 1/4".

Are all A-body rear axles the same dimension (52 5/8" flange to flange)?

I'm going to upgrade to 74 Dart front disk brakes, which I've heard will bring my wheels out about 1" on each side...so would using an E-body axle be fine when I have to change to new wheels, and that would allow me to get the same offset wheels front and back (as mentioned in this thread)? BTW, can I use 14" big bolt pattern wheels with 11.75" rotors? Or will I need 15" wheels?
 
Hetman said:
I have a 69 Barracuda with a 7 1/4" differential and am eager to upgrade, to 8 3/4" if possible but also am considering 8 1/4".

Are all A-body rear axles the same dimension (52 5/8" flange to flange)?

I'm going to upgrade to 74 Dart front disk brakes, which I've heard will bring my wheels out about 1" on each side...so would using an E-body axle be fine when I have to change to new wheels, and that would allow me to get the same offset wheels front and back (as mentioned in this thread)? BTW, can I use 14" big bolt pattern wheels with 11.75" rotors? Or will I need 15" wheels?
Click to expand...
Yes they're all the same width. Not positive on using 14" wheels but my guess would be no. Figuring that 14" wheels i.d. is a little less than 14" and the rotors are nearly 12" diameter that only leaves about an inch all the way around for the caliper to clear. I bet it'd hit
 
This might help.
Mopar_rear_axle_dimensions.jpg
 
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