8 3/4" swap info

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Claydart

MOPAR to the very bones
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Hi all, I decided to rebuild, and swap in a 8 3/4 in my dart now that I have a little more power under the hood. Tired 273 gone, healthier 340 in its place. I know there are a few things I have to do, but the one thing that has me wondering is, can I just figure the length of the driveshaft by subtracting the axle to yoke measurement from my spare B+T driveshaft, and having it cut down by 2.25" and welding back together. I will have a driveshaft place do the work, but can I just give them the measurement to build it, with the original u-joint yoke, and get a dual sized u-joint?
 
Safest thing to do is wit till the rear is on and do the measurements.

But technically you could measure your current axle centerline to rear U joint centerline and that of the 8 3/4 to determin how much to take off.
 
My A body 340 Demon has a 48 5/8 driveshaft
just for reference.
What year is your car?
 
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The parts books have dimensions and which rear end and trans combo it goes to.

BUT. You would be better off installing and measuring.
 
Difference at the yokes between a 7.25" rear and an 8 3/4 is 2.25". So if you changed from a 7.25 to an 8 3/4, changed nothing else, and the driveshaft was the right length before then taking 2.25" out of it should work.

Best bet would always be to measure. Measure twice cut once as they say.

My A body 340 Demon has a 48 5/8 driveshaft
just for reference.
What year is you car?

Looks like an early A, so what exactly is the Demon measurement good for? Also, that's not the factory measurement for Demon with an 8 3/4.
 
All sizes of driveshafts are known it you just post what body and trans you have...
 
Difference at the yokes between a 7.25" rear and an 8 3/4 is 2.25". So if you changed from a 7.25 to an 8 3/4, changed nothing else, and the driveshaft was the right length before then taking 2.25" out of it should work.

Best bet would always be to measure. Measure twice cut once as they say.



Looks like an early A, so what exactly is the Demon measurement good for? Also, that's not the factory measurement for Demon with an 8 3/4.

The gentleman did not state what A body Wheelbase he had or what transmission.
I did not assume that in his picture was his car he was currently working on!
I measured my Demon just to give him a starting point of reference as I stated.
The 108 Wheelbase is the most common of any of the A bodies.
The rear ride height and spring configuration will also affect the length a bit.
In anything except a restoration that is completely production original = You
need to measure it with the car with weight on rear end.

The reason I asked what year it was = I own a dozen turnkey A bodies with
all different Wheelbase and transmission combo and I would measure any
one of those on a 4 post ramp and give him my measurement that would get
him close enough to double check his measurements against.

What is a reference point good for = I have often mismeasured things the
first time around AND I do not trust charts without verify them.
 
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