SM420 Trans with a Model 20 rear end

Hi all, I am new here but I am a seasoned Jeeper. I am thinking of putting in a SM420 trans for a better crawl ratio in my 82 CJ5. I have the inline 6cyl, which is fuel injected, Dana 300 Transfer case, and the stock model 20 rear end. I recently put on a suspension lift and found my rear driveline had to be shortened (I currently have a T18 transmission). Has anyone done this conversion before? Were you able to still use the Model 20 rear end? If not, did you have to change to a different rear end and which one? Any help would be great. Thanks.

Wes

 

I would say that the 20 axle is ok for light wheeling if it still has two piece axles and 31" tires but they will eventually spin, replace with one piece axles and truss the housing and you may be able to handle up 35's depending on how you use it. For my money I would rather put a 4:1 gear set in the transfer case than change out a good T-18 (wr 1st 6.32 cr 1st 4.02) along with adapter length and driveshaft mods to fit the 420. jm2c

 

Why did they have to shorten the rear driveline with a lift? Unless you went high enough to need a cv you shouldn't need to shorten anything. I agree with dave74 go with the 4:1 in the t-case if you need lower gear than what the t-18 gives you. You will get more good out of that than changing the tranny.