T90 To T14?

Ok so im new to the forum but have read many posts on the website for years before making an account. so a little background info, and if this isn't the correct place to post feel free to lmk i have a '68 cj5 im doing a common sense/ minimalist restomod. so im changing things to improve drivability, but not going way over the top and making it too nice that ill be afraid to drive it. ive swapped out the F134 for a completely rebuilt chev 153 (or omc 2.5/ mercruiser 3.0, not completely sure which) its mated to a t90a via a novak GN9 and a dana 18 with warn od. i recently picked up a '70 cj5 as a parts jeep for cheap, and it had a 225 v6, t14, and D18 w/ OD that has all been rebuilt also. now im not interested in the v6 rite now because i did a Saginaw manual steering conversion, and the light weight and compact size of the 153 are perfect for that, and i can 1 hand the steering even at a dead stop. but im wondering if the trans t case combo would mount up to the chev bellhousing without any major mods? my t90 is a 2.79 first gear, and the 3.10 first of the t14 seems more appealing to me. i know id have to change the clutch disc, but i already have a new one that would work.

 

Sounds like a lot of work and expense for a 10% change. I would be more interested in a sm465, t18, or t19 since there will be a transmission rebuild anyway. What axle ratio are you running?

 

If the 153 uses the standard GM bellhousing bolt pattern, and the V6 has the 2 piece bellhousing with adapter, it should bolt up.

 

Im running 5.38. the only reason i even considered it is because i already have the t14 trans and t case and crossmember. it would also put my crawl ratio the same as my buddy who runs an ax15 and 4.11's in his yj.
actually i have a good sm420 sitting in my shop, but with the length of the adapter to mate it to the D18, and where the engine is placed in the frame, id get like an 11" rear drive shaft. and i think thats too short.

 

Another advantage to the T14 over the T90 is a synchronized 1st gear.

 

Yes. This is a distinct advantage.

The T-90 adapter has a different pattern from the T-14 adapter, so you need to keep the matching adapter whichever transmission you use. The T-14 shifts easily and is pleasant to drive around town. I'd guess parts are more available for the T-90 than the T-14. Realize that your T-14 has a different spline count on the output (10) than the T-90 (6) and you'll need an output gear that is 10 spline and compatible (tooth count, tooth angle) with your transfer case. Novak has a table of part numbers - The Novak Guide to Dana 18 & 20 Gears Interchange 1941-1979

I would go through the new transfer case before I used it. The Dana 18 is known for wearing out the intermediate shaft, and I would service the case with a new high-quality intermediate shaft and bearings (not Omix!) before I installed it. Also an opportunity to improve sealing and rebuild the parking brake, as needed. Lots of info on here about these topics.

If it's actually the 181/3.0 that's pretty cool. The 181 was available as a crate engine a decade ago, and saw industrial usage as well as boats. We have members with the 181 and the 153, if you have questions about the swap in general. Fine choice.

 

The t14 has a t case already mated to it, so output spline count shouldn't be an issue. whats the easiest way of checking the intermediate shaft and bearing status? and if they are bad do i need to remove the t case to replace any parts?

 

Since you can't drive it until it's together, I would say that you can't check condition without taking the transfer case apart. You could install it and run it and see how it goes. The intermediate shaft gets noisy as it wears. Unlike transfer cases with a centered rear output, all the engine power goes through the intermediate shaft. The shaft and bearings wear out relatively fast. Aside from leaks, that's the main issue with a Dana 18.

To me, rebuilding the transfer case is an easy bench job. You're going to have the transfer case on the shop floor anyway. I would go ahead and install the new parts, seal and adjust it. Same with the T-14 - I'd probably go through it and replace the blocking rings and front main bearing. Once on the bench, the work is easy and satisfying. Removing and replacing the transmission or transfer chase is not difficult with a Jeep, but most of the work is in the R&R.

Others here have infinitely more experience with the Dana 18 than I have, and could better make specific recommendations.