T90 Transmission

Cacti_Ken · Post by **Cacti_Ken** » Mon Mar 01, 2010 1:04 pm

Why would there be two different output gears in the T90 on some transmissions. Some have a 29 tooth gear and some have a 26 tooth gear.

idiocrates · Post by **idiocrates** » Tue Mar 02, 2010 9:19 am

That's an excellent question.....but I'd be willing to bet it doesn't have any kind of conclusive answer. Being as how the T-90 and T-18 have been around so long and both have been modified in so many ways (especially the T-18) I'd guess that it has to do with engineering attempts to make the T-18 more robust and durable. Like the three different intermediate gear shaft diameters....and the various gear tooth counts that are available all the way through the transfer case....the super T-18 and all the way up to the T-20...plus the ability to mate them up with bigger engines....bigger transmissions....and so forth and so on. Or maybe its just to make sure the guys out there doing the rebuilds are paying attention....cause it will bite you if you aren't careful. Then throw in the civilian requirements of the last few years....and.....well there ya go. The little T-18 should get a lot of credit for making a jeep what it is....and while you are calling the gear the transmission output gear.....to me its really the transfer case input gear.....so I suspect its the history of development of the transfer case that led to the various gear counts more than anything else. Just my $.02 worth....

Post by **wesk** » Tue Mar 02, 2010 10:14 am

Jim,
You almost got her figured out. D18 right? The T-18 is a 4 spd Warner Gear Box very akin to the T-98.

Gearing is dependent on application such as CJ, Wagon, Pickup, Willys, International etc. as well as power, 4 cyl, 6 cyl, 8 cyl, V6 etc.

idiocrates · Post by **idiocrates** » Tue Mar 02, 2010 11:24 am

Yeah.....what he said! T...D.....Model 18.....despite what you may be thinking......I'm not nearly as used as I confused to be. Me and a keyboard is kinda like a duck and a june bug.......once he finds one he keeps peckin away at it until he gets it.
The first thing I did when I started rebuilding my transmission and transfer case was count and record the number of teeth on all gears, measure lengths and diameters of all intermediate shafts, record spline counts, and document any and all shims found. Even with all this I still got fooled by the four wheel drive sliding gear on the front of the transfer case. Almost figured out.......right....pfffft.

Cacti_Ken · Post by **Cacti_Ken** » Tue Mar 02, 2010 6:01 pm

I called it the output gear because it is on the transmission shaft.
But I see in the parts manual it is called input gear.
Ok, different vehicle application. Would that have anything to do with the vehicles having different gear ratios in their differentials.

Post by **wesk** » Tue Mar 02, 2010 11:47 pm

Gearing covers the entire propulsion system. Tranny gearing, transfer gearing, differential gearing and tire diameter all are elements of the gearing equation. Vehicle weight, engine HP, preferred RPM operating ranges, and preferred driving speeds are the parameters that create the numbers used in the gearing system. Each is inter-related and in some way dependent on the other.

Cacti_Ken · Post by **Cacti_Ken** » Wed Mar 03, 2010 12:55 am

How would my M38 (that has a 26 tooth gear) function if I changed it to a 29tooth gear and changed the gears in the D18 to accomodate the change in the input gear?

Post by **wesk** » Wed Mar 03, 2010 3:35 am

Ken,
Nice try at trying to sucker me into doing the math for you!

You can figure the ratio's of the gear sets and compute the final drive ratio.

Cacti_Ken · Post by **Cacti_Ken** » Wed Mar 03, 2010 5:43 pm

Naw that's too complicated for me. It ain't that important anyhow. But I should take your answer you posted where you indicated different vehicles have different gears according to the weight, tires, engine HP, rpm operating ranges and so on and leave it at that.