Swapping A T-15 For The T90

Has anyone ever heard of or completed a swap out of a T-90 for a T-15 ? I have a T15 with a mated twin stick Dana 20 and a centered Narrow flanged Dana 44 with a locker. I'm thinking about putting this tranny into a 55 cj2a, behind the F-134. Has anyone done this in the past or know a link to a build thread where this has been done. Or last option, is this not possible?? Thanks

 

You will need an adapter plate from the transmission to the belkhousing. The T-15 input what is very much longer, the input pilot is a larger diameter, and the splines area for the clutch disc is much larger diameter. The input shaft is longer than the 4 cylinder T-90 input and the transmission is much longer. This means the driveshafts must be modified, the crossmember must be moved plus the transmission mount modified. The shifter will be in a different location which means the inside (floor) sheet metal must be modified for the transmission shifter and the transfer case shifter.

Is this a factory or aftermarket twin stick 20? If factory then it must be a Scout 20. Is the T-15 a Scout or Jeep? They are different in primarily the input shaft and front bearing retainer.
The front bearing retainer is another thing to think about as the throw out bearing you want to use may or may not be compatible.

All things to consider.

 

Thanks Nick. The T15 is out of a jeep and the Dana 20 is also out of the same jeep. The Dana 20 just has an after market twin stick conversion. Do we know if anyone here has ever attempted this one before. I just have a very nice tranny and TC along with a much better Dana 44 rear that I would like to use and this early 5 is a good candidate. I much prefer the T-15 over the 90 and love the ability to rock between R and 1st, if I get into trouble and also having the synchronized first gear. The T-15 behind a F-Head should be a worry free tranny. I just have never heard of it being done and I am always looking for more PAIN.

 

I have a T-15 behind my 4.3 Vortec in my 47 right now and like it a lot.

 

You may be in uncharted territory here. I've never heard of it being done but doesn't mean it can't. The adapter and pilot size would be the two biggest issues that I can see.

Edit: one other thing to think about is the first gear ratio and the jump to second gear being used behind the F-head. While 3.00-1 first gear isn't horrible it may not be that great behind your engine either. The jump from 3.00-1 to 1.83-1 is pretty significant behind a low hp low torque engine.

 

A custom or modified crossmember is always ideal whenever fitting non-standard engine/transmissions combinations

I would not consider a T15 / Willys 134 combination to be practical.
T15 maindrive gear (input shaft) is 1-1/8" diameter.
It's 10 spline and you will need a custom pilot bushing made up.

You must get into modified engine fore/ aft placement and or transfer case fore/ aft placement issues.
I just don't believe the 134 power band can justify all the fitment concerns.
Basically your only getting a smoother transmission and quiter transfer case out of the deal.

Dauntless / T15 / D20 fitment would be a completely different matter with far greater potential.

 

If I'm not mistaken the T90 stickout is 6-1/2" and I just measured the T15 stickout at 8-1/2".
The T90 = 8" OAL and T15 is 10" OAL so you need to figure 4" of added drive train length.
That also means a custom made 2" thick adapter plate.

Your clutch driven disk will have to be 1-1/8" @ 10 spline.
I happen to have a Kaiser NOS disk (Borg Beck) with 1-1/8" @ 10 spline.
It fits under the 9-1/4" Auburn pressure plates.
As far as that goes I also happen to have one of the NOS Auburn pressure plates.
I was saving these clutch parts in case I ever wanted to install the GM 153 engine to a T15.

 

I knew about the gear ratio difference on the T-90 and 15. I didn't think that that would be as big a deal as it sounds like now. I was going to see if chassis unlimited might have a bell housing or adapter or the normal channels like AA or Novaks. Right now I am weighing the pros and cons. Coming out with a smoother tranny and TC ain't to bad a deal. Cross members and engine and driveline placement is not make or break for me. Too short a rear driveshaft, could pose a problem, but a woods part may take care of that, but at what price? Coming out with a nice Dana 44 with extra splines and a selectable locker, not so bad with 11 inch brakes. I should start a pole and see where it goes. You have to admit, it does sound interesting and I like a challenge and just think, it could get a bunch of people thinking, what if.

 

nikmill, could the jump between gears be tamed by different differential gearing ? Making it a smoother transmission between gears when shifting

 

Personally, if I was going to do the work, I wouldn't do it for a three speed. If it's going to see mostly road use, a Saginaw car 4-speed would be my minimum, but I'm a sucker for that transmission.

I hate when people tell me this, but just because you have it laying around, doesn't always make it a realistic swap candidate.

 

If your T-90 is in good shape then I'd just use a T-86 rear bearing retainer to index the 20 transfer case and be done with it.

 

The gear split isn't going to be any different based on axle gearing and then you are changing the overall final drive ratio. Not the path to fix your problem.

 

A Saginaw 4 speed would have to adapted on both ends and then you get to cut up your floorboards for the shifter. And depending on which ratio transmission version you can find the first gear may not be any better. Even more work and expense than the T-15 he has now. Plus parts availability is seriously waning on these. I've been running a 3 groove wide ratio unit in my 59-5 since 1989.

I agree, just because you have it doesn't make it a good swap.

 

Agreed; the point I was trying to make was that if it's going to be a major job regardless, at least try to get a 4-spd out of the deal.

 

Yeah, I'd think you could figure out a way to get an all-synchro 4-speed or 5-speed, rather than the all-synchro 3-speed. There are Jeep 4-speeds (SR4, T4, T176) and 5-speeds (T5) that work with the New Process transfer cases, are top-shift, and I'd think would be plenty stout to stand up behind a F134. Your usual motivation for the T-15 is V8 power, since it's the only strong enough 3-speed option that also works with the Texas Pattern Dana 20. It may also be possible to use some more exotic parts like Geo/Suzuki/Hyundai trans and transfer case, since you are going to be inventing a way to mate the transmission to the engine anyway.

Another option is a T-98 that was optional for the F134. Then you'd have 3 speeds forward synchronized, plus the low 1st. It's not an easy shifter though.

 

I do have a T86 tranny kicking around. By the sounds of most here, the T-15 swap for the T-90 does not sound like a good choice. I'm disappointed. I was looking forward to finding a way to at least try it. My T-90 is not in bad shape at all and I even have a spare that is also in good shape, but the thought of having the T-15 is just following me around. The bearing retainer from the T86 and the Dana 20 and then centered 44 in the rear is still better than what I have, but that nagging possibility of rocking between 1 and R and having a down shiftable first gear........................................................... its just nagging at me.

 

Yeah I fully agree going from 1st to reverse and back should be a breeze.
A great way to get out of a deep midwest mud hole
And the T15 is plenty smooth shifting and strong for a little jeep.
It' really just that extra 4" of length that makes it questionable

 

Nag, nag, nag. Sounds like you have irreconciliable differences with that T-15. As your attorney, I strongly suggest you divorce it and get on with your life.
(that will be $5,000, payable now)

 

And excuse me if I didn't see it above, but unless regeared, the D20 is going to be 2:1 low range and the D18 2.46:1. That's quite a hit if you like to use it on any even slightly challenging trails. It's also quite a hit to the wallet to regear the D20.

IMO, time and money much better spent with many other options. I, like Nick, have been running some version of a wide ratio Muncie car 4 speed since the mid 70's. Currently, it's Auto Gear Equipment's wide ratio version of the M22 (2.56:1 1st gear). Those only really work well on the trail with an engine that produces significant bottom end torque. AGE now makes a version of that transmission with a 2.88:1 first gear. They do shift very smoothly and I have never worried about scattering them on the trail.

 

Just to note the difference, the (Muncie) M22 is an aluminum cased close-ratio trans, and the 3-groove Saginaw 4-spd is a wider ratio (3.50:1 first gear) cast iron case.