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T90C or not to T90C? That is the question. |
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smfulle 
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 Topic: T90C or not to T90C? That is the question.Posted: 07 Oct. 2015 at 4:11pm |
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So I spun a rod bearing and have pulled everything out of Grampa's Jeep, including the transmission and transfer case.
While I have everything out I am considering some gear changes to ge a little lower crawl speed. Also, I think I will add an overdrive. Looking at Herm the Overdrive Guy's website he seems to have a coulpe of different options. He has the D-18 transfercase with Tera-Low gears that give you 3.15-1 in low range. Looking at his transmission options, he has a T90C that has a 3:34-1 1st gear. What I can't figure out is if it would be better to get the T90C and marry it to my current t/case and the overdrive, or to get the Tera-Low t/case and marry it to my current transmission and the overdrive. Some of factors that I am thinking about: 1. My current transmission was rebuilt by me and it is the 1st and only transmission I have ever cracked open. It works and shifts, but it seems a little noisy and I can't seem to get it to stop leaking no matter what I do. To have a transmission built by someone that knows what they are doing would be nice. 2.The T90C seems to give one a lower crawl rate that the Tera-Low D18, but I honestly don't understand how all the numbers work out to moving-across-the-ground speed when you combine lower transmission 1st gear with a regular low range t/case, or a lower t/case gear with a regular transmission 1st gear. I'm a librarian and a history major. All this math and engineering makes my eyeballs bleed. 3. Herm's T90C is about $500 less than his Tera-Low D18 which is a huge factor to me. But being the world's cheapest man, I often go for the up-front-cheap-that-costs-you-more-in-the-end option. Lots of times buying the more expensive thing later because the cheap one didn't work out. I'd like to avoid that. Any opinions or experiences that you all might have would greatly be appreciated. Here's Grampa's Jeep undergoing surgery. Everything is out. Just got to decide what to put back in.  |
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jpet
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Posted: 07 Oct. 2015 at 4:36pm |
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The Teralow is the lower option.
Teralow/stock: 3.15/2.46 = 1.28 T90-C/T90-A first gear: 3.34/2.79 = 1.2
T90-A has a 2.79 first gear D18 has a 2.46 low range Diffys are 5.38 2.79*2.46*5.38 = 36.9 or 37:1 crawl ratio Change T90-A to T90-C 3.34*2.46*5.38 = 44:1 crawl ratio T90-A with Teralow: 2.79+3.15*5.38 = 47:1 crawl ratio ... and if you go all the way T90-C and teralow: 3.34 * 3.15*5.38 = 56.6 or rounded up to 57:1 crawl ratio |
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CJ2A #29110 "General Willys"
MB #204827 "BAM BAM" "We do what we can, and we try what we can't" |
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oldtime
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Posted: 07 Oct. 2015 at 5:06pm |
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If you will be happy having a slightly slower geared Willys then go with the T90 C.
It will be geared just enough lower so that you can notice it. It is about 10% lower in first gear. It's also lower in 2nd gear. The T90C is a simple conversion requiring no other modifications to the Willys. The Tera Flex transfer case has certain advantages and also a couple disadvantages. It will provide you with 25% lower gearing but only when shifted in "low range". In my mind the 3.15 (actually 3.16 if you do the math) is the absolute optimum transfer case reduction ratio. Optimum in part because Low gear @ High range = High gear @ Low range. In other words the only gearing repetition is 1st gear @ high range. The Tera Low 3.15 will require use of a big hole transfer case. For Tera Low to T-90 you will need to locate a special transmission rear bearing adapter. The required bearing adapter can be found behind 1966-1967 Dauntless powered CJ-5/6 with T86 transmissions. For Tera Low to T98A You will need to install a T18 rear adapter plate to fit the "big hole" index bore. Also the Tera Low transfer case will require using a special "bowl gear" if you plan on installing an O.D. The slowest possible gearing will only be available via installing a Borg Warner T98A transmission. That transmission alone will provide a 50% gear reduction. Half as fast as standard gearing. The T98A installation is much more involved. Read: http://cj3b.info/Tech/T98A.html These modification effect your stock crawl ratio. The Standard CJ-2A crawl ratio = 37/1 CR If you double that number "37" then it becomes half as fast T90C = 44/1 CR TL 3.15 = 48/1 TL 3.15 plus T90 C = 57/1 CR T98A = 84/1 CR T98A plus TL 3.15 = 1.09/1 CR |
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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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smfulle
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Posted: 07 Oct. 2015 at 6:09pm |
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Thanks jpet and oldtime.
All this is definitely food for thought. I think if I am reading Herm's website right, he has used the small hole d18 and ground the cases for the Tera-Low. Not sure if this counters the adapter requirements you state or not. I really don't want to make my rig into a "crawler." I still want to drive it around town, but I do love to take on the rocks from time to time. Also didn't want to go to the 4 speed and change the original personality of this CJ2A. And of course, the budget plays a large part in this decision. Hmm...
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oldtime
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Posted: 08 Oct. 2015 at 12:50am |
Yes it is possible to put 3.15 gears into a small hole transfer case but it is impractical to do so. One would essentially have to grind a hole through the small hole transfer case to allow for intermediate gear clearance. Then one needs to weld an ugly patch over top of that same hole. It is certainly do-able but that obviously yields a weakened transfer case. Yes using the small hole case negates any need for a T86 rear bearing adapter. I do have a OEM NOS bearing and rear adapter that is required to mate the T90 into a big hole transfer case. I will likely sell it before long, but not until or before I sell my last T90C transmission. If T98 4 speed has been ruled out then I suggest that you should modify with the T90 C. Like I say T90 C is the cheapest and easiest change you can make toward lowered gearing. "Cow bell" is running the T90C with no other gearing modifications at this time. Go watch his recent videos... |
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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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jpet
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Posted: 08 Oct. 2015 at 2:09am |
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CJ2A #29110 "General Willys"
MB #204827 "BAM BAM" "We do what we can, and we try what we can't" |
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Oilleaker1
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Posted: 08 Oct. 2015 at 1:29pm |
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I believe Colorado has turned Jpets attention to rocks. My wife found a card on her cardmaking sites that shows a Jeep with it's front tire parked on top of a rock. It says: It's Just a Rock-------Get Over It!
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Green Disease, Jeeps, Old Iron!
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pjensen641
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Posted: 08 Oct. 2015 at 5:28pm |
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If you go with a T90C, I would suggest the 30% OD. It ends up splitting the gears better than the 25%. plus gives you a little better top end.
If you stick with a T90A, the 25% is better match for splitting, the 30% is too much. I put the first combo behind my Kubota diesel. With a 2000 RPM rev range, the T90C wider ratios are at the maximum limit for shift points. In direct drive, the jump from 2nd gear to 3rd forces me to run up to my 2800 RPM max revs in 2nd on order to get to 3rd at about 1200 RPM. An original L134 won't be as bad, but it will be noticeable that you must rev higher before shifting. With the 30% OD, I can split by running 2nd OD and then jumping to 3rd direct. Almost a perfect split. It makes you feel like an old school trucker  . Its surprisingly easy to do.Offroad, the T90C seems to be a significant improvement. However, the Kubota is such a huge change, that I can't really make a good comparison. I can basically put the thing in 1st low and let it idle over the rough stuff. I use the OD more offroad than on due to the perfect gear splits. The T90C + 30% compliment each other so well that the sum is better than the parts, so to say.
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pjensen641
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Posted: 08 Oct. 2015 at 6:08pm |
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Here are some gearing charts I worked up to visualize the gear combos. You can see how nice the T90C with 30% overdrive is split. The speed is calculated with stock 5.38 final drive and 28" (600 X 16) tires. You can ratio from there for larger tires.
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pjensen641
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Posted: 08 Oct. 2015 at 6:20pm |
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Here are some Low Range Charts comparing standard and Terra Low gears. Again, this is 600x16 tires
I really wonder how useful the Terra low is with stock-ish tires and 5.38 gears? How often do you have so much traction that you can crawl that slow up an obstacle? Often, you have to have some speed to overcome an obstacle. If you were running 33" tires and 4.56 gears or something it might make more sense. I also worry about project creep personally. A T90C and OD is a simple and cheap operation, even starting with the original gear cases.   Edited by pjensen641 - 08 Oct. 2015 at 6:25pm |
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smfulle
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Posted: 08 Oct. 2015 at 9:35pm |
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"Project creep" is where I'm always at.
Thanks for the charts. They really help me to understand the numbers. I'm pretty math challenged. I have this little jeep on some pretty good rock crawls and it has performed amazingly well. I have wanted an overdrive since I first got the wheels turning. Panting for a lower crawl ration has come along as a result of my rock crawling experiences and also as a result of watching the "Qwaazy Eight" on Chinaman Gulch at this years Fall Color Tour. You've about sold me on the T90C and the 30% overdrive. I've posted this before, but this is what we like to do and why I'm thinking about a lower gear. |
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oldtime
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Posted: 09 Oct. 2015 at 1:23am |
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Yeah those charts are excellent for visualizing the "gear split proportioning".
But what they don't reveal is the limitation of the L-134 engine. Because of meager power I am sure that the Willy 134 engines are better off with no higher than a 4.03 compound final drive ratio. I drive a lot of interstate with my rig so I tried to get more speed out of my strong running CJ-3B. I had the typical 5.38 differential ratio in my 3B and I always run mine with a 25% overdrive. 5.38 differential ratio X 25% O.D. yields a compound final drive ratio of 4.03. I switched my differential ratio to 4.88 gearing and the Jeep performed very notably worse. So bad that I switched it right back to 5.38's before the week was through. The F-134 simply could not handle that meager gearing increase. 4.88 gears roughly provides a 10% change over the 5.38 gears. If my strong running Hurricane could not handle 10% gear increase then I'm fully certain that the Go Devil will not be able to handle even a 5% speed increase. In other words if you have a Go Devil engine you'd best stay somewhere below a 4.03 compound final drive ratio. Perhaps 30% O.D. is desirable on perfect flat ground or for running down hill with a Go Devil But the slightest uphill I am fully convinced that the 30% O.D. gearing will be a definite liability. |
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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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Lee MN
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Posted: 09 Oct. 2015 at 1:50am |
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X2 what Oldtime said. I run a standard OD in my 2A, it runs very well, but a 30% OD is not going to happen with a L head engine, just not enough oats there to pull it!
 ...... Interesting thread.Lee 
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LEE
44 GPW-The Perfected Willys 49 2A “If you wait, you only get older” 67 M715 American Made Rolling History |
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jpet
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Posted: 09 Oct. 2015 at 1:57am |
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Just to be clear, I don't think pjensen641 is suggesting a 30% OD for higher top end. He's just suggesting it for better splits off-road with a T90-C which is what Stan is most interested in.
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CJ2A #29110 "General Willys"
MB #204827 "BAM BAM" "We do what we can, and we try what we can't" |
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Lee MN
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Posted: 09 Oct. 2015 at 2:39am |
Yes, I understand that, Just say'in the 30% is going to be a big disappointment on the road and that needs to be considered as well. Lee
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LEE
44 GPW-The Perfected Willys 49 2A “If you wait, you only get older” 67 M715 American Made Rolling History |
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pjensen641
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Posted: 09 Oct. 2015 at 3:48am |
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Yeah, I have no experience with the L-134 and 30% OD. Best to take others advice on that. I forget how limited they are.
The Kubota would like a 40% OD if one was available :-). I plan to run some 215/85-16s to get a little lower revs at 55. Next year maybe :-). I suppose just as important, my charts show why you would never run a 30% OD with a T90A. Almost no gear split. Starting to look like maybe the Terra Low would be better for Stan and his rig.
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smfulle
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Posted: 09 Oct. 2015 at 6:37am |
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Well dang, I did think of the Go Devil being a little short on ponies.
I'm not looking to go 65, but 55 would nice. The chart shows about 2500 rpm st 55 mph. I wonder if it couldn't really do that? Seems like I remember General Willys topping out at a little over 50 in overdrive. I'm sure he has the 25% overdrive. I would hope that I could at least get some of the road benifit of an overdrive while getting all the variety of offroad gear options. This afternoon I had decided on the t90c and the 30% overdrive. Now I'm not sure. |
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jpet
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Posted: 09 Oct. 2015 at 9:24am |
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GW can do well over 60 with 25% OD. Even without OD he can do 60+ but in both cases the pedal is hammered
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I think if I am reading Herm's website right, he has used the small hole d18 and ground the cases for the Tera-Low. Not sure if this counters the adapter requirements you state or not.