7 1/4 to 8 3/4 swap question about driveshaft length

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Chryslerkid

Chryslerkid

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hi guys,

i am getting ready to swap my stock 7 1/4 rear end for an 8 3/4 rear end. I currently have a '71 dart 2-door, 727 transmission with a 7 1/4 rear end. my question is, how much if any, will i have to cut from my current driveshaft to fit the new 8 3/4 rear end? i have the driveshaft from the other car, but it was a 904 transmission to the 8 3/4 rear(so i assume it won't bolt in without fabrication). All of the parts i am using came out of a '72 dart so everything should fit....i hope. any thoughts or info is appreciated. thanks
 
mounting points and yokes can vary slightly so the only true way to do it is to install everything then measure it .
 
I always recommend measuring it after you install the rear. It would need to be measured with full vehicle weight on the rear suspension.

What I did when I swapped mine, I called the local driveline shop and asked them "how" they wanted it measured. I did so and it came out perfect.

There is one other possibility here, and I'm not up to speed on this, BUT if the 727 slip yoke will fit on the other driveshaft, it might work. Someone else can chime in on that.

What ever you do, when you put the shaft in (as in experimenting), just because it might fit with the rear hanging, doesn't mean it will when you lower it to the ground.
 
Not gonna work because the tranny's are different length and the rear ends are different sizes and pinion lengths as well , you hit the nail on the head call the local drive shaft guys and ask how they want it measured , it can often be done the same day if they aren't too busy and you get it in early .
 
my 1967 dart factory service manual shows a 6 cyl with a 7-1/4 rear end has a drive shaft length 54.61.
the 273 with 8-3/4 rear end has drive shaft length 52.58 BUT i dont know the the difference of the trans length. or if the back end of the engine being in the same place. both for manual 3 and 4 speed and auto trans.
 
My documentation does not show any Mopar 727 transmissions with a 7 1/4 rear end. The documentation shows a 70 340 Dart with 727 and 8 3/4 rear has driveshaft length of 47.99".
This should be used as reference ONLY! As everybody else said " you should measure and do as your driveshaft shop tells you". This should give you a ballpark idea of the right length, hopefully.
 
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