Low gear transfer case swap advice

Lotta good points so far, one of the great things about this forum. Dvader made a good point that swapping to a T18 only gives you a granny gear as the 2nd,3rd and 4th gear ratios between the T15 and T18 are the same. It also gives you strength in the form of bigger internals. I've got a T15 and a T150 laying out back you can have (they're very broken) hence my swap initially to a T18. I also wanted to go slower for the rock crawling here in AZ. Nickmil gave us the crawl ratio options for the T18 and Teralow which confirm just how much we'll gain by the different swaps; all good info. But let me throw in another option. Don't overlook the NP435 as a choice for a T15 replacement. Not only does it have a slower first gear (6.69 as compared to the T18's 6.32) but it also has a lower 2nd gear (3.34 as compared to the T18's 3.09) which will not only benefit you in low range but high range 2WD as well. I had originally put a T18 in my 75 but after a year I pulled it and put the 435 in. That was 17 years ago and I've been totally happy with it. It has the same bellhousing bolt pattern as the T18. If there is a downside at all it would be that the 435 is an inch longer than the T18 and the adapter is 2" longer than the T18 adapter but my rear driveshaft is still over 15" long and I have no problems. I finally broke down and spent the money on the Teralows and now I'm at nearly 80:1 crawl ratio but with 3.73 axle gears I can do 65-70 down the highway all day long. Like nickmil said you just gotta look at what best fits your needs. Also, when I was researching all my options I made up a spreadsheet with gear calculations for various combinations of transmissions and transfer cases. If anyone wants a copy, shoot me a PM.

 

I've got the wide ratio T-18 and a TeraLow kit and it works great. With 4.56 gears it's about mid-90's crawl ratio which works well even in rocks with 35" tires.

 

Dunno where my mind is at today. The NP435 is actually a little over an inch SHORTER than the T18...gotta learn to proofread.

 

IMO the main downside of the NP435 compared to the T-18 is a lack of any junkyard swap for the NP435. The T-18 (and T-19) can be adapted with junkyard parts, either starting with the Jeep T-18 or using parts from a Jeep or IHC T-18 (or IHC T-19). If the advantages of the NP435 outweight the additional cost of an aftermarket adapter kit, the adapter is available for the NP435 from Novak and also Advanced I presume.

 

I have been keeping my eye on this one TC from STaK 4X4 which is a 3 speed TC and different gear options. I just tried their website and it is not coming up. They had many options...I think up to a 6:1....has anyone tired this in a CJ? Could it fit?

 

I recently ordered a 3-speed Mini-Box from STAK, should be readt for me to pick up next week. It is a direct bolt in replacement for the D-300 I was running, just a tad bit bigger. It is coslly, but has the advantages of being clockable so I will be gaining over 5 inches of clearance under the belly and it comes with choice of yolks and the shifters included. It's medium gear is like 2.97 :1, compared to the 300's 2.62:1, and the low gear is a massive 5.22:1, which will put me at a 90:1 crawl ratio.

When I started looking to upgrade I considered the Atlas 2, which runs around 2300$, but when you consider also having to buy the yolks I needed as well as a quality twin-stick shifter and then pay shipping on it all, the STAK 3-speed min i-box became a real bargain at 2499$ as it was 100% complete and it is local so I can pick it up and pay no shipping, add to that the extra gear and for me it is a no-brainer. I will have all the swap details posted later in the build thread.

Weigh all your options before committing, if I hadnt I'd be in the middle of rebuilding & trying to upgrade the 300 right now.

Oh, and for some reason their website is down right now, but their phone number is 915-584-2400

 

IIRC the Stak and Atlas are not adaptable in place of a D20. They do not support the "texas" bolt pattern. They do, however, bolt into any circular d300/NP mounting bolt pattern.