Tera Low

Instead of changing my stock t14 trans to a sm420 for the low first gear, I am considering a tera low kit for the d18 t-case. Any opinions on sm420 vrs tera low. Leaning towards a tera low, because it will only require modifing one componet.

 

The Tera Low is something most amateur mechanics could do in a weekend; the scope and amount of the work is not comparable to the transmission swap.

A truck 4-speed will give you that really low 1st gear ... the Tera conversion won't approach that. IIRC, the Tera Low goes from a 2.46 ratio to 3.15 ... something like that. That's a change of roughly 28% better. The SM465 changes your 1st gear ratio from 3.1 to 6.55, or 111% change, a difference of about 4 times.

So, the Tera gears are an improvement , but not really comparable to the truck 4-speed.

 

So your opinion is that the would be a better swap as far as money and time goes. It seems that I see more people swapping in a sm420 than installing a tera low. Is this because they are intimidated by installing the tera low or is the sm420 simply a better swap.

 

It kind of depends on you. The scope of the two projects is very different.

 

witch one would you choose to do or are you happy with your jeep just the way it is.

 

Haha. I can't make the decision for you.

I'd do both, but I'd also pick a different transmission. Plus I have plenty of other things to do before I get to that point.

 

if more than 50% of the Jeeps usage is going to be crawling in the rocks, go the sm420.
my 0.2 worth

 

Re: Terra Low

Its poring down rain here in Redding Ca today, norther Ca. Used to have smaller tires and 488 gears. Now I am running 31 9.5's and 427 gears. Now I'm not real happy with my low 1'st gear. I won't be making any changes until next winter, unless I have problems with my trans or t case.

 

This is definitely a decision only you can make.
I will start by saying that 90% of my Jeeps use is rock crawling and the tranny swap cost about $1500 total.
After I put the SM465 in my CJ, I considered the Tera Low gears. Right now the crawl ratio is around 76:1. With the Tera Low gears it gets down to around 99:1. For the cost of the gears it really doesn't seem like it would make that much difference. The tranny is a beast and I doubt I could ever hurt it in any way. I understand with the Tera Low kit there is come clearancing of the t-case that needs done.
For what it is worth the tranny swap was one of the best mods I ever did, right behind the Detroit Locker. I don't use first gear alot but it is great for going down rocks or on really technical stuff, just drop the clutch and let it idle over things. BTW reverse is equally as low, definitely a good thing.

 

Re: Terra Low

Sorry I thought I saw that you had 4.27's. What gears do you have in the pumpkins?

Quick Calculations on crawl ratio. Diff gears 4.27, Stock D18 2:46
T14 32.5:1 Current
Tera Low 41.7:1 w/T14
SM420 73.5:1 w/stock D18
SM420 94.1:1 w/Tera Low gears
SM465 68.8:1 w/stock D18
SM465 88.1:1 w/Tera Low gears

 

Re: Terra Low

I have 4.27. The sm420 or sm465 seems to be the way to go. I guess I need to start looking for a trans and misc. parts. Study the swap, this should make things go smothly. The reason I am talking about trans vrs tera low is that I just don't hear much talk about the tera low. Most of the jeeps seem to have a trany swap, and there must be a reason. Thanks for your opinion. May need some help and tips on mistakes some people may have made so I don't make them. It seems like after doing some projects you wish you had done it a little diffirently.

 

Re: Terra Low

The pinion gear in the front axle broke, a dana 27. I used to have 4.88 gears. They no longer make the 4.88 gears so I regeard to 4.27 gears. I also have a overdrive. I now wished I had been a little more patient and look for a good set of used 4.88's or lower. Not to happy with my crawl ratio now. Seems you guys are pretty happy with the sm465. If you could do the trans swap over would you still go with the sm465 or the sm 420.

 

Re: Terra Low

Thud. When did this happen?

There's always the classifieds or a 4.88 D30.

I'm a little confused, your sig line says you've got a T-18 installed.

 

Re: Terra Low

clint
the D27 4:88s have been disco for quite a while
used is all that's out there.

 

Re: Terra Low

antony - your sig line says T-18 (truck 4-speed trans) but maybe you meant D18 which is the stock t-case. Or, I'm just confused.

I looked in to the tera low thing before putting in the SM420 and it just didn't look like the way to go for me.

I can tell you that it's a huge difference with the SM420. Having the real low 1st and reverse makes a big difference at certain times.

In your case if you went back to 4.88's and the tera low it would help some and would be less work than the trans swap.

As to which trans, just do a bit of research and keep your eyes out for a good one. It may just come down to what you find first or for the right price. The sm420, 465, and T-18 are all heavy duty and most have the low gearing.

 

Re: Terra Low

Personally I'd go with a T-18 or SM-465. If all you want is the lowest first gear possible then the SM-420. Reason I'd go with T-18 or SM-465 is parts availability now and in the future. Remember, the SM-420 hasn't been manufactured since 1967, You're talking 42 years and parts can be very hard to come by and expensive. I recently rebuilt one for a customer. Front bearing retainer was missing. Finally found a used one in ok shape for $65. None of my usual transmission supply houses (warehouses who don't sell to the public) had one or could round one up. Just an example.

 

What Nikmil said. SM 420 is a great tranny but getting real hard to find around here, especially parts. When I installed my 465 it needed some parts because of water damage. I went to a local tranny shop and the guy had 3 or 4 on the shelf.
As far as would I do it again, in a heartbeat!
Oh yeah, paid $50 bucks for the 465.

 

Don't forget the NP435, it's a Dodge/Ford tranny but Novak has adapter plates for it.

 

Re: Terra Low

http://www.jeep4x4center.com/jeep-axle-differential-parts/dana25-27-front-cj-willys.htm

4.88 gears are all they list for the 25/27 front axle.