7 3/4 to 8 3/4 swap only

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josekh7

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Hey guys so i came across a rear end where the seller is willing to swap rear ends for my small 7 3/4 from my slant six. Now my rear end is currently in the car which i still use. What do i need to do this swap so i can drive off the same day. My dart has its original 904 transmission and slant 6. His 8 3/4 rear end is coming out of a 340 v8 duster. Woukld the drive shaft need to be cut ? or can i just bolt it on and go?
 
josekh7 said:
Hey guys so i came across a rear end where the seller is willing to swap rear ends for my small 7 3/4 from my slant six. Now my rear end is currently in the car which i still use. What do i need to do this swap so i can drive off the same day. My dart has its original 904 transmission and slant 6. His 8 3/4 rear end is coming out of a 340 v8 duster. Woukld the drive shaft need to be cut ? or can i just bolt it on and go?
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Not sure on driveshaft length...you'll just have measure both to see. You will need 8.75 shock plates and U- bolts.
 
Don't forget to bleed the rear brakes - but will the lines fit? Better compare your current brakes with the ones going in.
 
I did the swap in a '70 Dart when I was 17. I was disappointed to find out that with everything bolted up, the driveshaft would not fit. It was not off far so I ended up taking the rear back out & drilling new holes in the perches for the alignment dowels in the leaf springs to make it work.

Your 7 1/4 rear should have the small u-joint, but 8 3/4s can be small or large. You can get a 'crossover' u-joint from big to little if needed.
 
I did what you are going to do on my car. The drive shaft needed to be cut a fraction over 2 inches. I tried measuring it and came up with that amount, then discovered the specs in the driveshaft section of my 67 Plymouth shop manual which confirmed my measurements.
 
the width of 7 1/4 and 8 3/4 third members are different. you also have difference in wheelbase. quit possible the 340 has the larger u joint no doubt. your slant has the small ones. ya better soak the brakes lines if you will be able to take off and reuse? like he said different u bolts and mounts.

remember NOTHIN ever goes as planned.
 
You didnt say what year anything is but you could easily run into a much larger problem than driveshaft length...I would be willing to guess that a /6 Dart is going to be SBP and its quite possible that the Duster is BBP, in other words, your wheels might not bolt back on!!! Check bolt pattern on both vehicles BEFORE you pull any parts off.

Measure from front edge of one stud, skip one and then measure to front edge of next one. That will be either 4" or 4.5"
 
magnummopar said:
You didnt say what year anything is but you could easily run into a much larger problem than driveshaft length...I would be willing to guess that a /6 Dart is going to be SBP and its quite possible that the Duster is BBP, in other words, your wheels might not bolt back on!!! Check bolt pattern on both vehicles BEFORE you pull any parts off.

Measure from front edge of one stud, skip one and then measure to front edge of next one. That will be either 4" or 4.5"
Click to expand...

If its a stock A body 8.75, it is guaranteed to be small bolt pattern. When Mopar changed the A Bodies to the 8.25 integral axle is when they also changed to BB pattern.
 
Check bolt pattern on wheels, I believe all 8-3/4 had small pattern. Also, right rear may have left hand threads.
 
65Val said:
If its a stock A body 8.75, it is guaranteed to be small bolt pattern. When Mopar changed the A Bodies to the 8.25 integral axle is when they also changed to BB pattern.
Click to expand...

You are probably right, I have two BBP 8 3/4 in shop but they were probably converted, one has non stock axles. Other might be redrilled, but now that I think about it, I have never pulled the hubcap off....front is BBP but....selling 8 3/4 rear disk kits in BBP throws me off :D
are all 7 1/4 SBP? I know not all /6 are SBP, my 74 sport /6 has BBP 8 1/4
 
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