Low gear transfer case swap advice

I have a buddy who wants a lower geared tcase he has a 304,t15 with a stock 20 tcase and was wanting a Atlas case.
but they, A/A say it wont fit, behind the t15 in his 73 cj5.

What options could I recomend?

 

Tera low makes a set of low range gears for the dana 20. its 3.15:1 vs the 2.05:1. Its around a thousand bucks.

 

IIRC Teraflex has a 3.15 low range kit for the D20.

Found it for you
http://www.teraflex.biz/products/low20-manual.html

John

 

Yep, atlas not available/adaptable to the texas pattern d20.

3 options,

1) t-18 or some other granny gear trans

2) tera-low KIT, 3.15 low I've got this, it works GREAT.

3) swap in a scout D300, has a 2.46 LOW. these cases are hard to find.

 

Or a combination of 1 & 2.

 

T18 worth every penny, IMHO.

 

I am not sure the tera low kit alone would be enough for him.
he wants more options on the trail.

It looks to me the t15 is the real problem.
The bell housing is not compatible to the T18
And the t15 is not compatible to the Atlas

But that would be nice to use Teralow t20 and the T18 combined.
trying to keep the driveshaft lenght in mind...

Could you use a different bellhousing?

I see Herm has both think I'll call him tomarrow too.

 

the tera low does not add any length. THe t-18 only adds about 1.5". a bellhousing from a cj with a t-18, t-150, or t-176 will bold right up an accept the t18.

 

The t-18(wide ratio)/Terra Low Dana 20 combo gives you 7 effective gears from 1:1 to 20:1. You multiply that by the axle gears and you get your final drive.

I.E. with 4.56 axle gears that gives you a final drive of 91:1 in 1st gear low range.

The above is what I have and it is great on the trails and on the road.

Also do a search here for short shaft t-18 to get an idea of what you will need to do to make it as short as possible.

 

There's lots of info buried in the forums about the T-18 swap. Search for the intersection of nickmil and T-18. He knows more about these swaps than anyone else on these boards, IMO.

The T-18 can be done at least a couple of ways using junkyard parts, or you can buy the adapter kit from Advance or Novak and swap in a 2WD Ford T-18.

The only way you can reuse the T-15 bell is if you find a T-18 from a 1970-79 258 (258 only!) Jeep pickup or Wagoneer. This transmission will fit the bell, but it is not the shortest combination available. If you find one of these, it is essential that you get the plate adapter that goes between the transmission and bellhousing. Won't work without it.

Otherwise you will need a new bellhousing from a Jeep CJ T-150 or any Jeep T-176. The bell from a SR-4, T-4 or T-5 CJ will also work, but it will need to be drilled to fit the transmission.

Really, the bellhousing side is the easier side to deal with. You either need parts from a junkyard Jeep or IHC T-18 to adapt the transfer case side, or one of the adapter kits. A Ford 2WD PU T-18 plus the kit would be the easiest, but the kit is ca $600 IIRC.

 

You could put a Teralow kit in an IHC Dana 300. Then you would have 4 to 1 low range.

 

Talked to Herm today and my buddy.

Herm thinks just start with the T18 conversion might be enough then if he wants more we could still do a teralow kit later.

Herm has the newer bellhousing we'd need.

Not sure about the clutch linkage yet but thats what were leaning towards.

 

I am a big fan of T18s, but I don't think your buddy is going to get what he is looking for. The 1st gear in his T15 is 3.00 to 1. The second gear of a T18 is 3.09 to 1, almost the same as the T15. What he will get with the T18 is one new crawler gear in low range. Once he shifts to second, it will be like he still has his three speed. He will also see a high range benifit in that he will have a granny gear to start out in, if need be.
If what he wants is more usable lower gears, he should consider a SM420 with a 7.00 first and a 3.60 second, or an SM465 with 6.55 first and a 3.58 second, or a NP435 with a 6.68 first and a 3.34 second.
Since he was considering an Atlas Transfer case, I am going to assume that money is not a big issue. In that case, I would take the opportunity of a tranny swap to also change to a Dana 300 set up. Then he could use the Dana 300 stock, with a Teralow, or go ahead and get the Atlas.

 

Money is never a free for all but if its gets what he wants then its there.

I was woundering about this issue too.

frankly I dont have enough real world experience to answer.

Will the t18 on its own meaning one real low gear really be enough to satisfy rock crawling needs...

How does the sm420 convert to the 304?.

I have the sm420 in my Commando but havnt tried it as yet.

 

Honestly I did the t-18 route before the terra lows. It was ok but there were still times I needed slower wheel speed. Adding the terra-low kit to the t-case in addition made a world of difference. I am very happy with the way its working now. A lot of my wheeling is done now in second or even third gear low range.

I say start with the t-18 and see if he likes it. If he decides its not enough then put the terra-lows in the t-case.

 

The Ford transmissions (T-18, T-19, NP435) are easier, but the Muncies are not difficult. Novak has a page http://www.novak-adapt.com/knowledge/420_to_amc.htm about adapting the SM420 to AMC engines. Lots of good info on the Novak site.

 

Just a vote for the t-15...

I love my 3 speed, strong, reliable, already there. I have always liked the R to 1 positioning as it is way easier to do a 15 point turn around with it like that.

I struggled and struggled with the same choice, Teralow in the case (whichever case) would be what I would say and what I did. I am very happy with my 3 new lower gears. Plus less than $500 and 1 day to do the work I put what I was going to spend on the t-18 and got an OX locker.

 

The 77-79 Jeep bellhousings have the dual mounting holes that the T18's use. The NP 435 will also bolt right up to this bellhousing. When I did my swap 17 years ago I got one of those bellhousings from a wrecking yard to put a T18 in. I pulled it and put a 435 in a year later.

 

You can run the D18 gears with the rear slider out of an early bronco 20 to get the 18 lower low range in your 20.

 

Let's do some basic final crawl ratio math here.

Stock T-15, don't remember the exact first gear ratio but let's use 3.0-1 as a basis for comparison.
Stock model 20 transfer case, 2.03-1
Don't know what axle gears but let's say 3.73-1

3.0x2.03x3.73 = 22.7

Right now he has a 22.7-1 crawl ratio.

Change transmission to a T-18 with 6.32-1

6.32x2.03x3.73=47.85

Now has roughly a 48-1 crawl ratio

Back to stock transmission and upgrade transfer case to 3.15 (Tera, JB, etc)

3.0x3.15x3.73=35.2

Now has roughly 35-1 crawl ratio

Now lets change to a T-18 and low range conversion

6.32x3.15x3.73=74.2

Now has roughly a 74-1 crawl ratio

We could continue all day by changing to an aftermarket transfer case like an Atlas or a STAK or by different transmission and transfer case combinations but this gives an idea what the most dramatic change would be without changing axle gear ratios. The transmission hands down is the biggest change in this formula without spending big bucks (read Atlas or Stak) if you are simply looking for lower gears. Any of these combinations are good ones, just gotta look at the one that best fits your needs.