7 1/4 to 83/4 swap - A Body

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ClarkDart70

ClarkDart70

Street Machines Limited
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Ok, I'm looking to buy a 8 3/4 open diff from a forum member to swap out my 7 1/4 for.
What can I expect during this swap?
Will the drive shaft need shortened?
Will the U joint sizes be different?
Will my 14" rallyes fit or will I need to look at 15" due to larger drums?
Any axle width differences?

I am trying to keep this as straight forward as possible.

Thanks FABO!

Clark
 
Plenty of threads on this subject but here's a quick run down . You'll need the following .
Larger u bolts
8 3/4 " shock plates or modify The ones from your 7 1/4" to fit the larger u- bolts
Yes your d/s will need to be shortened
Install the axle get measurements and have a reputable shop build you a New d/s
Chrysler uses two size u joints determine which your differential has and have your d/s built with that size u- joints and yoke.
If this is an a-body axle the width should be the same .
and if the brakes are stock your wheels should be fine.
You don't state what cars are involved in this swap.
Therefore I am answering on the assumption that this is between two a body mopars all stock with SBP .
 
Sorry... coming out of a SBP Duster and into a SBP Dart. Thanks for the info. I found a local DS shop and they can build what I need (at a price of course!). Thanks again!
 
The only reason I'm going to contradict the gentleman that said you'll need to shorten your driveshaft is because I just walked in the door from putting brakes on my 8 3/4 rear that came out of a 70 Dart and am about to install in 69 Barracuda. If you have access to the Direct Connection chassis book it will explain in great detail what you need to do. But I know the 7 1/4 third member extends forward at the yoke than does the 8 3/4 so you'll need to have a driveshaft made that will be roughly 2-3 in. longer. As far as wheels they should be the same.
 
So, I guess I have getting conflicting info on the drive shaft. I read before that I needed roughly 2 1/4" taken out, but is the current drive shaft actually going to be too short requiring a longer one like MoparMike said?
Also, will the U joints be different sizes? Do they make a U joint that will adapt the 8 3/4 to the 7 1/4 drive shaft? I know I had to do this when I swapped an 8.8 into a jeep a few years back.
 
When removing a 7 1/4, and installing a 8 3/4, the driveshaft needs to be shortened.
There are two different yokes possible on the 8 3/4 rear. I forget the number designations, but there is a large and a small. On an "A" 8 3/4, it should be the small yoke, unless it had been changed in a prior life, that is the same as on the 7 1/4 rear. If the 8 3/4 rear has the large yoke, there is an adapter u-joint available, at most part stores. Don't remember the part number, but if you need one, send me a pm, and I will look it up.
I just installed one of these joints on my 66 Valiant, when I installed a borrowed 4.88 chunk that had the large yoke.
 
Awesome! Thanks Charlie. The 8 3/4 came from a 71 Duster and is going into a 70 Dart. Maybe I'll catch a break and they'll be the same U joint size.
 
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