Dana 18 To Dana 20 Conversion Advice

Robert, your post so I will answer you first.
To begin with changing your 1971 cj from Dana big hole D18 to become a D20 becomes quite involved.
It can certainly be done but you must be committed to many other directly related changes.
There are several Dana 20’s that can work and this in part depends on your transmission selection.

Twin2, most D20 castings have shaft recesses provided excepting the very latest C18-15-24-8 version.

Robert again you can use any of the cases marked 24-1 and later excepting the final casting ending in 24 -8.
The -8 has no recess pockets required to fit earlier transmissions.
The “24” implies big hole (4” index bore) and the “8 “ signifies the revision sequence.

Again I repeat ..... they are not D18 nor D20 castings.
All are embossed with either a “10” implying small (3-5/32”) index or “24” implying big (4”) index bore.

 

This is tcase I picked up over the weekend...original D18 for a 70 CJ V6. Its the -5 version like posted above. It has an interesting tag on the back too...

 

947384 = CJ5/CJ6, V6, with standard transmission, with 4.88 axle ratio, used with T-14 transmission, single shift lever control.

 

Except it had 3.73's....

 

3.73 TC for a 1970 CJ would be #947383.
The only difference would be the tag itself and the speedometer driven gear.
The driven gear can easily be changed.

 

Minor mystery i guess....i know the history of this jeep since it was bought hew in California in 70, and it originally had 3.73's