7 1/4 TO 8 1/4 Swap

-
JR

JR

Pissed off senior member.
Joined
Oct 17, 2005
Messages
4,404
Reaction score
18
Location
East Renton,WA (Seattle)
Just wondering if anyone has done the swap and NOT changed the driveshaft. I have been hearing from guys that say "It's no problem" and others that say "oh god, your going to die if you don't change the driveshaft". What about changing the drive shaft but not right away, how long before anything gets screwed up?
 
Been there, done that. They are different lengths, but I don't remember the number. I thinks I have seen it on here and I know I have seen a chart showing the difference between 7 1/4, 8 1/4, and 8 3/4 axle centerline to pinion yoke.
 
You need to shorten the drive shaft about 1.5" to maintain the 1-2" of travel in the slip yoke at ride height (it will be less at full extension or compression).
 
The difference is 1.6" between the two.

What exactly will end up being the problem, worn seals, bearings, u-joints or the end of the known universe? I'm not talking the stock mopar to the book specs here I am talking real world experience. I won't be leaving it like that forever just a few months of daily driving.
 
If you don't shorten it you could slam the yoke into the tailshaft of the tranny, like on a speed bump or other situation that causes the rear to move.
 
Dido what BW dart said...if you max out the suspension, you could hammer the yoke into the tranny. When i swapped my 7-1/4 to an 8-1/4, the driveshaft would not go into the rear u-joint at all, which made me shorten it. good thing, because if i did, it would have been a big mess!
 
You could move the rear back 1.5" to make up for the longer driveshaft. Most spring perches have two extra holes in them, just drill the one in the front to fit the centerbolt in the spring.
 
It cost me $60 to shorten and balance the drive shaft for the swap. Easy stuff to do. Hardest part was waiting for it to be done. And you need it done.
 
.are these 8 1/4 rears good to build for mild hp applications?..seems everyone wants the 8 3/4 rears..looking to swap my 7 1/4 sometime..
 
mine road to far in the trans and wore the rear house and bearing out of the trans/ was going to swap the old three on the tree for a four speed/ but i ran it that way for 2 or3 years as a daily driver and drove it from fla. to ohio . never let me down
 
I did the swap few years ago, Had it shorten 1"an 3/4's cost me 75.oo dollars, Other than that no problems used the same leafs
 
You must log in or register to reply here.
-

Back
Top