Model 18 and 20 swapability?

For the life of me I cannot find an answer online. Will a large hole model 18 bolt to a tranny that came with a model 20?

Ok, found it, I think. Same bolt pattern. Will depend on input shaft spline count. I think?

 

Yes, a large hole 18 will bolt where a 20 was and vice verse. The key is the transfer case input gear and what transmission they are bolting to. With Jeep manual transmission all were a 6 spline output shaft except the T-14 (both V-6 and I-6 models) which were 10 spline and had to have not only the correct spline count, but the correct tooth count and tooth pitch to match the transfer case gears. There were variations like the ones used behind the T-150 ('76-'79 CJ) that had a seal surface machined in the gear. LOTS of variations which is why you have to have the correct input gear # to match the transmission and transfer case you are using.

Novak Enterprises has one heck of a database showing what works with what.

When you get into Jeep Auto transmission there are different gears that must be used, also listed in Novak's database.

 

Be very careful! I once bolted an 18 t/c to a T15 trans. Everything seemed OK till I got on it hard & broke 3 mounting ears off the transfer case Turned out, the shaft for the reverse idler gear stuck out just a little too far for the transfer case to bolt up flush. I wound up buying a model 20 case & putting the 18 guts in it, but I could have accomplished the same thing with a little grinding on the model 18 case to clear that reverse idler shaft.

 

Doh! Forgot about the reverse idler shaft and counter gear shaft sticking out.

Good catch Colojeepguy

 

Well, false alarm. went to go look at a "t98 just pulled from 77 CJ, transfer case is somewhere in the shop too..." , price was right, I was thinking it was really a T18 with the 6.32 first gear, 77' was right year. Well, here is what I get for thinkin', an early ford t98 2wd. Wah, wah,wah. Gotta love craigslist.

 

Some D20's have the machining done so the ilder shaft will not interfere with the mounting.

 

i have a dana 20 i behind a t 14 i put dana 18 guts in the t case i just grinded the reverse idlier shaft down flush to bolt up the t case no problems yet