The specifics of converting an E Body 8 3/4 rear end housing to an A body 8 3/4 rear end houseing

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ethan santin

ethan santin

Buck eye jim you gotta go
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Hello There FABO

I am going to be converting an E Body 8 3/4 to fit my 1972 duster. I have already done some research and looked through the sticky thread "An accurate 8 3/4" rear axle width list". I wanted to reach out to any members here on the forum who have converted an E body 8 3/4 to an A body 8 3/4 and ask about what sorts of issues you ran into as well as any specific measurements you decided on shortening the rear end to, as well as leaf spring perches locations. I am also interested in what kind of BBP axel options are out there for A body 8 3/4's and what you would personally recommend for this kind of swap. Any and all information about converting an E body 8 3/4 to an A body 8 3/4 would be greatly appreciated. I understand that deciding to use an E body 8 3/4 to adapt to an A body is the least appealing option because of the overall difference in size between an A body rear and an E body rear but its all I got.

Thank you for reading, hope you have a great day!
 
I can narrow your rear end to A body length and specs if that’s what you’re looking for. I’m in San Jose, and have narrowed dozens of 8 3/4 and 8.8 rear ends. If you can weld and have a jig you can do it yourself also.
 
Once you have to narrow an 8.75 it's all the same, whether you want to chop it down to run 15" wide tires inside the wheel wells or if you want to convert an B/C/E body into an A body. Basically you're going to look at that list and cut it down the the specs needed for an A body. Then you're going to need a jig to put it back together that has a rod that goes all the way through from one side to another and through. It's impossible to put it backtogether (correctly) without a proper jig. It's not an easy job, but not impossible for someone to do at home.
As for axles, spring perches and other odds and bits go to Dr. Diff. I got my bbp axles there and I have always been super happy with their service
 
Cass@ Dr. Diff.com is your man. Reach out and talk to him. He has everything you will need to accomplish what your doing, and knows what he is talking about.
 
What are your plans for wheels/tires?

I ask because you may not want to use A-body 8 3/4 specs. DoctorDiff can sell you custom length axles, the price difference is pretty negligible. On a Duster the factory rear track is substantially narrower than the front track, and depending on your wheel choice it may be better not to run the factory width.

Since you’re moving the spring perches already, you may also look into DoctorDiff’s 1/2” spring offset, which will buy you some extra space for wider tires.

Not saying to have to do either, but just considerations. I run a 68-70 B body 8 3/4 in my Duster at the B-body width, with a 1/2” spring offset and 295/40/18’s on 18x10’s.
 
72bluNblu said:
What are your plans for wheels/tires?

I ask because you may not want to use A-body 8 3/4 specs. DoctorDiff can sell you custom length axles, the price difference is pretty negligible. On a Duster the factory rear track is substantially narrower than the front track, and depending on your wheel choice it may be better not to run the factory width.

Since you’re moving the spring perches already, you may also look into DoctorDiff’s 1/2” spring offset, which will buy you some extra space for wider tires.

Not saying to have to do either, but just considerations. I run a 68-70 B body 8 3/4 in my Duster at the B-body width, with a 1/2” spring offset and 295/40/18’s on 18x10’s.
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Great, thank you so much for all the info, I will definitely be looking into all of DoctorDiff.

As far as my plans for wheels/tires, I would like to run 15x8s in the rear with a large tire, probably a 275.
 
what wheel specifically? wheel offset plays into it as well. when I measured my duster, the 7.25 rear is 57.125" wide drum face to drum face (where the wheel mounts). the factory SBP rims are 14x5.5 and measure 3.75" BS (so +1/2" offset). when I measured the tires to the inner fenderwell and the inside of the wheelwell lip, the tires are about perfectly centered. if you're using a 0 offset wheel, the rear would need to be an inch narrower to get the tire centered again. if you plan on using a high offset wheel (like a Mustang Bullit, which is +30mm/1.2" offset), you'd want the rear 1.4" wider, which would put you at about 58.5" wide to get the tire centered again....if you wanted to use say, late model mustang rims (2005-newer, +45mm, 1.75" offset), you'd want the rear to be more like 2.5" wider than factory A body spec.....
 
ethan santin said:
Great, thank you so much for all the info, I will definitely be looking into all of DoctorDiff.

As far as my plans for wheels/tires, I would like to run 15x8s in the rear with a large tire, probably a 275.
Click to expand...

For 275/60/15’s on a Duster with a 15x8 and BBP axles you’re basically looking at using the standard A-body 8 3/4 housing width. The BBP axles widen the track compared to the SBP axles, and a 4.5” to 4.75” backspace on a 15x8 is about what you need to center the wheels.
 
Well, here's my story : 72 duster . I put in an 8.25 out of a 75 dart. Meant to be a temporary rear so I could get 4.5 BC on the car until I could build a proper rear.. Put on 15x8 4.5 BS with 275/60-15. Clearance to the outside was great. Clearance to leaf spring was very tight. Would sometimes rub the spring and inner wheelhouse on tight turns. I narrowed an 8.75 to stock Abody 52 5/8 width , put the perches at 42 and used the Dr Diff 1/2 offset shackles and hangers. Dr Diff axles and big brakes. Now , plenty of space between tire and spring . Tire is too close on outside. Rubs on Quarter lip on hard bumps. Trimmed the lip . Tire still rubs the outer wheelhouse on hard bumps . If I was to do it over, I would have made the housing a little narrower, maybe 52.00. A 4.75 BS wheel would fix it , but that size is not as common as the 4.5 . Moral of the story : It is better to be too narrow than too wide. You can always add a wheel spacer.

duster 8-31-21 003.JPG


duster 3-5-23 002.JPG
 
72bluNblu said:
What are your plans for wheels/tires?

I ask because you may not want to use A-body 8 3/4 specs. DoctorDiff can sell you custom length axles, the price difference is pretty negligible. On a Duster the factory rear track is substantially narrower than the front track, and depending on your wheel choice it may be better not to run the factory width.

Since you’re moving the spring perches already, you may also look into DoctorDiff’s 1/2” spring offset, which will buy you some extra space for wider tires.

Not saying to have to do either, but just considerations. I run a 68-70 B body 8 3/4 in my Duster at the B-body width, with a 1/2” spring offset and 295/40/18’s on 18x10’s.
Click to expand...
Yep i am doing exactly this, i got a 8,3/4 cheap. Got the Dr diff 1/2 inch offsets and running a 8.5inch rim with a 275 and a 3.5inch back space, so i will shorten diff accordingly hopefully be able to fit inside the guard line.
 
forphorty said:
Well, here's my story : 72 duster . I put in an 8.25 out of a 75 dart. Meant to be a temporary rear so I could get 4.5 BC on the car until I could build a proper rear.. Put on 15x8 4.5 BS with 275/60-15. Clearance to the outside was great. Clearance to leaf spring was very tight. Would sometimes rub the spring and inner wheelhouse on tight turns. I narrowed an 8.75 to stock Abody 52 5/8 width , put the perches at 42 and used the Dr Diff 1/2 offset shackles and hangers. Dr Diff axles and big brakes. Now , plenty of space between tire and spring . Tire is too close on outside. Rubs on Quarter lip on hard bumps. Trimmed the lip . Tire still rubs the outer wheelhouse on hard bumps . If I was to do it over, I would have made the housing a little narrower, maybe 52.00. A 4.75 BS wheel would fix it , but that size is not as common as the 4.5 . Moral of the story : It is better to be too narrow than too wide. You can always add a wheel spacer.

View attachment 1716189634

View attachment 1716189635
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This has me nervous as i am a 3.5 back space going to have to cut the diff so i am super close to the offset leaf. Main issue with the duster is no point even trimming the quarter guard lip as the wheel well also dives in rather than straight up

IMG_1537.jpg
 
Ozyduster said:
This has me nervous as i am a 3.5 back space going to have to cut the diff so i am super close to the offset leaf. Main issue with the duster is no point even trimming the quarter guard lip as the wheel well also dives in rather than straight up

View attachment 1716189661
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Yep, and the area of the outer wheelhouse that makes contact with the tire is very stiff and not easily "clearanced" with a big hammer . You can cut and modify the outer wheelhouse , but my car is already painted. In my case, I have a narrowing bar and pucks. If I ever get too annoyed by it , I have another housing I will cut.
 
Ozyduster said:
Yep i am doing exactly this, i got a 8,3/4 cheap. Got the Dr diff 1/2 inch offsets and running a 8.5inch rim with a 275 and a 3.5inch back space, so i will shorten diff accordingly hopefully be able to fit inside the guard line.
Click to expand...
an 8.5" rim with 3.5" backspace is -1.25" offset. to use that wheel you'll need to probably make the rear end more like 54-55" drum-face-to-drum face. if you're looking for potentially less expensive alternative, starting with a ford ranger 8.8" out of a 2002-2011 FX4 gets you 31 spline axles, likely a 4.10 limited slip, and if you can find 2 right hand axles in a junkyard, (the pumpkin is offset 1.5", so the RH axle is 3" shorter than the LH), you can narrow 1 side and you'll end up with a rear that is 55.5" wheel mount to wheel mount.
 
Thank you for all the responses so far everyone, they have been very helpful.
And thank you for all the information on the kind of products DoctorDiff provides, I had not heard of them until I read some of the responses.
 
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