T90C vs T90A and Terra Low D18?

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   Interesting comments - I agree that driving skill, watching the Jeep in front of you (if you are not leading), reading the trail, understanding the limitations of our Jeep all play into to this.  Trails change over time, at least out there in fly over country.  They seldom get better with time.  Maybe your rock trails are static from 1974 - ours are not static.  There are times here  when you can spend several days and never drive the same trail and then it will poor rain and you can spend 7 hours trying to get 6 capable Jeeps with experienced drivers off a two mile trail loop.
But back to the topic of gearing.
I drove a CJ2A with a T90c off-road for years.  When trail riding with other Cj2a/3a/3b's that had stock T90A1 transmissions - It was impossible to match their speed on the trail (1st low) and I ended shifting up into second every now and then to catch-up  to the next Jeep.  But if the Cj2a/3a/3b's that are currently going on the Vintage Rubicon type runs have the T90c and Tera lows then matching their speed for the basic trail driving parts alone would make the trip more enjoyable. 

I was looking through my parts on hand and have two empty T90 cases one is a standard T90A1 the other is a T90E1.   Probably will uses the T90A1.  What is a T90E1? - any magic gearing for it to consider?

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Stev Members Profile Send Private Message Find Members Posts Add to Buddy List Member Sponsor Member Joined: 27 July 2016 Location: Cincinnati Status: Offline Points: 2391	Post Options Post Reply Quote Stev Report Post Thanks(0) Quote Reply Posted: 09 Aug. 2018 at 2:03pm
	Interesting comments - I agree that driving skill, watching the Jeep in front of you (if you are not leading), reading the trail, understanding the limitations of our Jeep all play into to this. Trails change over time, at least out there in fly over country. They seldom get better with time. Maybe your rock trails are static from 1974 - ours are not static. There are times here when you can spend several days and never drive the same trail and then it will poor rain and you can spend 7 hours trying to get 6 capable Jeeps with experienced drivers off a two mile trail loop. But back to the topic of gearing. I drove a CJ2A with a T90c off-road for years. When trail riding with other Cj2a/3a/3b's that had stock T90A1 transmissions - It was impossible to match their speed on the trail (1st low) and I ended shifting up into second every now and then to catch-up to the next Jeep. But if the Cj2a/3a/3b's that are currently going on the Vintage Rubicon type runs have the T90c and Tera lows then matching their speed for the basic trail driving parts alone would make the trip more enjoyable. I was looking through my parts on hand and have two empty T90 cases one is a standard T90A1 the other is a T90E1. Probably will uses the T90A1. What is a T90E1? - any magic gearing for it to consider?
	Stev 1946 CJ2A Trail Jeep (The Saint), 1948 CJ2A Lefty Restored

oldtime Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4186	Post Options Post Reply Quote oldtime Report Post Thanks(0) Quote Reply Posted: 09 Aug. 2018 at 4:30pm
	On longer trails with few stops its certainly easier to run with similar geared jeeps. That' just another reason why some would consider installing multiple crawling ratios. Only those 2 ratios were ever available for T90's. So it's either !8 main drive teeth or 16. No others ratios were made. Many variations were built due to maindrive diameters and shifters. Besides the maindrive and the countershaft gear. There is only one other difference between T90-A and T90-C. The oil collector was omitted with T90-C and so the T90-C case casting has the bosses that are not drilled to accept an oil collector. If your T90 case is drilled for an oil collector you can simply plug those tapped holes... Edited by oldtime - 09 Aug. 2018 at 4:32pm
	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

Stev Members Profile Send Private Message Find Members Posts Add to Buddy List Member Sponsor Member Joined: 27 July 2016 Location: Cincinnati Status: Offline Points: 2391	Post Options Post Reply Quote Stev Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 2:16pm
	More Questions: -Is it better to use the Dana 20 case over the Dana 18 case for the Tera-Low? - Is the Dana 20 just stronger? - Dose the Dana 20 case hang down below the skid plate or hand up on the frame or hit the floor? Thanks, Stev
	Stev 1946 CJ2A Trail Jeep (The Saint), 1948 CJ2A Lefty Restored

oldtime Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4186	Post Options Post Reply Quote oldtime Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 4:08pm
	All Dana model 20 transfer cases are built using big hole (4" index bore) cases. But a big hole case does not mandate it was from a Dana 20. Jeep Dauntless 225 CJ's have single stick Dana 18's and those also use big hole cases. The obvious difference between the two similar cases will be that big hole cases all have twin shift rail thimbles exiting the rear of the case. The big hole cases are larger in the area where the intermediate gear resides. Furthermore, one may note that not all big hole cases were identical. There are certainly some minor variations from one big hole case to another. For example the 1970' s era big hole cases have the fill plug located above the rear output cap. So the the lube fill plug may not be on the right side as all D-18's have it. The large hole case itself takes up no more space than a small hole case excepting the shape change surrounding the intermediate gear. Not absolute mandatory but I certainly feel its best to use a big hole case because it takes little to no internal grinding to make Tera Flex gears fit inside. Small hole cases may become paper thin in that area in order to clear the larger diameter Tera Flex gears. The main difference is how the transfer case is to be built. Is it built to become a D18 or to become a D20 ? The ultimate Dana 18 is built inside of a large hole case. Basically it is a Jeep V-6 case that's been modified using a factory twin stick front bearing cap. Yes it also has twin thimbles yet both are not used. Anyway this must have Dana 18 shift rods not the Dana 20 shift rods. The shift rods will be specific for either the single stick or the twin stick shifters. I always prefer the factory twin sticks in lieu of a factory single stick. I also prefer to keep the propeller drum parking brake. I consider 3.15 reduction to be ideal for use with most all Borg Warner Jeep transmissions.
	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

3A Steve Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 10 June 2016 Location: West Virginia Status: Offline Points: 880	Post Options Post Reply Quote 3A Steve Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 4:21pm
	I went to a Tera Low in my 3A early this Spring. I didn't really need it for local WV trails but in Moab this May it was a different experience than last year without it. Without the Tera I did Hell's Revenge (minus the tubs, escalator, and Hell's Gate) and other than having to overuse my brakes which can be dangerous it went fine without the lower gears. Fins and Things This year was steeper and the Tera was quite useful. The biggest difference was in Canyonlands on Elephant Hill/Bobby's Hole. I had run it two years earlier with the stock setup (and no lockers) and it was unpleasant to say the least. Engine kept dying and I banged stuff up going too fast and having to slip the clutch. This year it was not a problem. Kept running and was relatively easy. Did break a shock but that gave me the opportunity to put some better ones on. Should also mention that I was at Uwharrie and Brown Mt in NC last month and the gears helped a good deal on the hardest trail at Uwharrie and the least hard trail on Brown (which is harder than the hardest trail at Uwharrie). If you can afford it get it. Must say the overdrive has made the most improvement of anything. It is a joy to be able to run at 45 to 50 without loosing your hearing or blowing something up. Isn't really all that useful off road but sometimes it does smooth things out a bit.

Stev Members Profile Send Private Message Find Members Posts Add to Buddy List Member Sponsor Member Joined: 27 July 2016 Location: Cincinnati Status: Offline Points: 2391	Post Options Post Reply Quote Stev Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 4:56pm
	3A Steve - Are you using the large hole (Dana 20 case) set up as with the Dana 18 parts plus the Tera-Low parts? Assuming you are have a Dana 44/41 rear and not a center diff rear end. Assuming yes since you reference the OD. OldTime - Good information - So the Dana 20 case gets stripped and the Dana 18 parts get bolted to it - so it is configured as a Dana 18 with a 1 1/4" cross shaft. Which Dana 20 case is best to use (photo would be a great help)? "Yes it also has twin thimbles yet both are not used." What are "thimbles"? "Anyway this must have Dana 18 shift rods not the Dana 20 shift rods." Can the current Dana18 shift rods be used in the Big hole case or are they something special for this adaption? "The shift rods will be specific for either the single stick or the twin stick shifters."
	Stev 1946 CJ2A Trail Jeep (The Saint), 1948 CJ2A Lefty Restored

oldtime Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4186	Post Options Post Reply Quote oldtime Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 5:07pm
	Probably makes little to no difference which big hole case you use so long as its not from a Ford Bronco. They will all be somewhat stronger than a small hole casting. The shift rail pockets at rear of case look similar to sewing thimbles. Shift rods will normally fit a specific front bearing cap (front outtput casting) Yes re-use your D18 shift rods and D18 twin stick bearing cap.
	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

oldtime Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4186	Post Options Post Reply Quote oldtime Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 5:14pm
	Here's a big hole case set up as a Dana 18 . Has Jeep Dana 18 twin sticks and propeller parking brake. This ones only 2.46 ratio because here you see it mated to a T98-A.
	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

3A Steve Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 10 June 2016 Location: West Virginia Status: Offline Points: 880	Post Options Post Reply Quote 3A Steve Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 5:34pm
	Mine is a large hole D-18 from Herm the Overdrive Guy. He has a strong opinion that the large hole D-18 is the way to go. Beats me. Yes the diffs are 25 and 44.

Stev Members Profile Send Private Message Find Members Posts Add to Buddy List Member Sponsor Member Joined: 27 July 2016 Location: Cincinnati Status: Offline Points: 2391	Post Options Post Reply Quote Stev Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 7:30pm
	3A Steve, Point of Clarification - "Large hole D-18 is the way to go" means - Dana 20 case set up in the Dana 18 configuration? Correct?
	Stev 1946 CJ2A Trail Jeep (The Saint), 1948 CJ2A Lefty Restored

3A Steve Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 10 June 2016 Location: West Virginia Status: Offline Points: 880	Post Options Post Reply Quote 3A Steve Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 7:42pm
	My understanding is that the large hole D-18 was used in late 60's early 70's. Oldtimer can probably clear that up. From my conversations with Herm I understood that use of the D-20 was something to be avoided... at least he got upset when I brought this up. Not that he is that hard to upset. Again, Oldtimer can weigh in. Chasendeer was looking into a Tera gear set but I believe he ended up with a 4.10 Rockeater. Maybe you can ask him where he got it and how it worked out.

bobevans Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 31 July 2005 Location: Pittsburgh, PA Status: Offline Points: 844	Post Options Post Reply Quote bobevans Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 8:32pm
	Stev, From what I can find, there were large hole D18 cases used. They were primarily used in the V6 CJ5s, maybe like '67 - '71. I have been trying to find one, but they seem pretty hard to come by. They will have the large 4" indexing hole ("big hole case") and already have the proper, offset outputs and block off plate to use as a D18. There are some folks, apparently Herm is not one of them, who say the actual casting, wall thickness, etc, is better on the D20 case.
	'48 CJ2A '56 DJ3A '79 CJ7 And two of them actually run!

oldtime Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4186	Post Options Post Reply Quote oldtime Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 10:40pm
	F-134 engines only ever had the small index bore of 3-5/32" All Jeep small hole transfer cases were twin sticked. Large index bore Dana 18 "single" stick was used on all V-6 CJ 1966 through 1971. Jeep nor anyone else ever built the big hole D-18 with the twin stick front bearing cap. It's easy to build one and makes for the the finest possible off road transfer case. Installing of a D18 vs D20 is somewhat a separate topic all it own. There are basic pluses and minuses to both transfer cases. I have weighed some early vs late big hole castings and yes they can and do vary at least 1-1/2 pounds from one to another. that said it's not apparent that some are thicker nor are they machined significantly different than another to make that 1-1/2 pound or so of difference.
	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

oldtime Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 12 Sep. 2009 Location: Missouri Status: Offline Points: 4186	Post Options Post Reply Quote oldtime Report Post Thanks(0) Quote Reply Posted: 10 Aug. 2018 at 11:28pm
	Some big hole cases are tapped for clutch control pivot balls and some are not. For T98 and T18 traqnsmissions the lever/tube assembly clutch controls will pivot from the pivot stud that is mounted on the transfer case adapter plate. Note that this one is an actual D20 case. If the fill plug is located at the rear it must be a D-20 case. Here I have 2 Dana 18 gear sets. They have 4 gears. Fcatory 2.46 and Tera Flex 3.15 Here you see a Tera Low bowl gear compared to a Standard Warn O.D. 29 tooth bowl gear. Here yu see a D18 3 gear set plus special bowl gear. Here you see 2 identical Tera Low intermediate gears except one has tapered intermediate shaft cups. installed Tapered bearing intermediate shaft kit. Perhaps the best way to reduce excess noise in a Dana 18. If your Dana 18 is going to have lots of hiway time this could be helpful. Compare to the standard intermediate shaft set. Here you see a Tera Flex 5 gear set. An extra gear is required inside the Dana 20 transfer cases.
	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

chasendeer Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 24 Feb. 2012 Location: Napa,CA Status: Offline Points: 1088	Post Options Post Reply Quote chasendeer Report Post Thanks(0) Quote Reply Posted: 11 Aug. 2018 at 12:05am
	You can leave the T90a in it for better around town gearing, and install a Rockeater Dana 18 in 4.1:1. That way you have town gearing and crawling gearing. Jay

3A Steve Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 10 June 2016 Location: West Virginia Status: Offline Points: 880	Post Options Post Reply Quote 3A Steve Report Post Thanks(0) Quote Reply Posted: 11 Aug. 2018 at 12:25am
	Jay, I have the Tera in my 3A but have been interested in your Rockeater. I now have a 51 Wagon with the Lightning 6 and am thinking of lower gears since it (I think) has 4.10 diffs. Where did you get your Rockeater and how do you like it? Steve

chasendeer Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 24 Feb. 2012 Location: Napa,CA Status: Offline Points: 1088	Post Options Post Reply Quote chasendeer Report Post Thanks(0) Quote Reply Posted: 11 Aug. 2018 at 2:01pm
	I got them from Jack himself. I have about 100 miles on the case, no issues other than leaking oil!!! O'brains four wheel west is who makes them. Jay

Stev Members Profile Send Private Message Find Members Posts Add to Buddy List Member Sponsor Member Joined: 27 July 2016 Location: Cincinnati Status: Offline Points: 2391	Post Options Post Reply Quote Stev Report Post Thanks(0) Quote Reply Posted: 15 Aug. 2018 at 2:03pm
	Thanks for all the advise on this Transfer case and Transmission. Here is where I ended up: Large hole DANA 20 case configured as a JC2A Dana 18 with Tera-Low and set up to run a Ramsey PTO1 out of the back for the front winch. The parking brake is stock for now - Hopefully will develop a mechanical disc emergency brake down the road. Transmission will be configured as a T90C. Starting to order parts for this build. Thanks, Stev
	Stev 1946 CJ2A Trail Jeep (The Saint), 1948 CJ2A Lefty Restored