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T90a to T90c...need for clarification |
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gunner 
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Joined: 05 Dec. 2005 Location: NW Status: Offline Points: 157 |
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 Posted: 27 Jan. 2014 at 2:33am |
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That's about what I thought too. I'm hoping to get the trans done this spring, but the DJ project has priority since I'm using a friends' shop and the jeep has been in there long enough already.
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Jeff J
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Joined: 12 Mar. 2018 Location: USA Status: Offline Points: 441 |
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Posted: 12 Mar. 2018 at 12:45pm |
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I ran into a situation where it is cheaper for me to install a T90C cheaper than I can replace the 2 worn out gears in my T90A. I understand top speed will be about the same. Anyone have a review on how the T90C drives with the 5.38 differentials?
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oldtime
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Joined: 12 Sep. 2009 Location: Missouri Status: Online Points: 4184 |
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Posted: 12 Mar. 2018 at 2:56pm |
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Regardless of manufacturer: all transmissions excepting those equipped with O.D. have a 1/1 ratio in high gears.
So top speed will not ever be effected by the transmission itself. The T90 A and the T90 C utilize different ratios for 1st and 2nd gears. For T90A the 1st gear ratio is 2.798. and for T90-C it's 3.339. The 1st gear normally used for on-road is what I prefer to call the TAKE-Off ratio. For road use you multiply the 1st gear ratio by the DIFFERENTIAL RATIO. (DR) T90-A with 5.375 DR = 15.03 or 15/1 TAKE OFF RATIO. 15/1 TAKE OFF ratio is the time proven Willys standard. T90-C with 5.375 DR = 17.95 or 18/1 TAKE OFF RATIO. Multiply those figures by your transfer case reduction ratio to achieve the exact crawl ratios. The time proven standard Willys crawl ratio is 37/1. With T90-C your new crawl ratio will be slowed down to 44/1 ratio. It takes at least 5% change to effect a barely notice-able difference in gearing. Most typically 10% changes are considered at noticable. T90-A to T90-C is approximately a 15% change so it will definitely be noticeable both on-road and off. Because the 1st gear is notsynchronized; with T90-C you may find the jeep now capable able to do rolling stops at STOP signs. Because 2nd is also lowered you may find it easier to not use 1st gear at some stop signs. The common yet technically Illegal rolling stop.... |
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Currently building my final F-134 powered 3B .
T98-A Rock Crawler using exclusive factory parts and Approved Special Equipment from the Willys Motors era (1953-1963) Zero aftermarket parts |
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Rick G
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Joined: 17 May 2015 Location: Amarillo, TX Status: Offline Points: 1467 |
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Posted: 12 Mar. 2018 at 5:58pm |
I really like my T90c and 5.38s. I really don’t notice the difference driving around town. If you do notice it, you’ll get used to it. Plus it is much better offroad. I recommend it.
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Stev
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Posted: 12 Mar. 2018 at 6:26pm |
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Rick G. - I have T90c with 5.38 differentials. In low range, it is hard to match the speed of a stock CJ2A when trail riding. Great otherwise.
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Stev
1946 CJ2A Trail Jeep (The Saint), 1948 CJ2A Lefty Restored |
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smfulle
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Posted: 12 Mar. 2018 at 6:52pm |
I too have the T90C in my 2A. It has been an asset off road. I have noticed that I need to leave it in 2nd gear just a little longer when driving on pavement or the 60 horses of the Go Devil strain a bit when I shift into 3d. Not really an issue considering the up sides on the trail. As Oldtime mentined, I may, or may not execute a somewhat abbreviated (read rolling) stop at some stop signs so that I can just leave it in 2nd and not have to stop dead or grind it into 1st. Having an overdrive makes it much easier to match the trail speeds of others in your group. |
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Jeff J
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Joined: 12 Mar. 2018 Location: USA Status: Offline Points: 441 |
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Posted: 12 Mar. 2018 at 9:52pm |
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Thanks all for the input. It looks like I will be saving some time and money by installing the “C”.
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Oilleaker1
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Joined: 06 Sep. 2011 Location: Black Hills, SD Status: Offline Points: 4412 |
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Posted: 12 Mar. 2018 at 11:09pm |
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My 1951 M38 has a T 90 C. 5:38 gears. The jump from 2nd to 3rd sucks. You will want a overdrive like I did. When pulling a good hill on the highway, the jump from 2nd to 3rd is too much. The OD is a thing of beauty with a T 90 C. The crawl is noticeable and welcome in the woods. If you go with Terra flex gears in the transfercase, you will need to buy the special bowl gear to go with it. Enjoy. John
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Green Disease, Jeeps, Old Iron!
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Rick G
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Joined: 17 May 2015 Location: Amarillo, TX Status: Offline Points: 1467 |
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Posted: 13 Mar. 2018 at 4:11am |
This is absolutely true. If there is a hill or long incline, you are not going to like driving the T90c without an overdrive, or rather the people behind you won’t like it😉. There’s an overdrive in my near future because of this. In town, you won’t notice it much, but on a highway hill you will. Hope I didn’t mislead you earlier. All in all, it is still worth it if you do any off-roading at all.
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Jeff J wrote: