One more question... Axles gears

One more question for yall before I probably wont have the internet again for a while

With the 304/t15/d20 setup, a planned Eaton E Locker in the d44, running 31's or 32's, what ratio should I go for? I was thinking 4.10

I wasn't planning on regearing when I first started but now with the plan for the locker I figured to consider new gears as well.

 

Just the typical moderate trail/creek driving

 

Hard to go wrong with 4.10s and 32" tires. That gives you a decent ability off road using low range, but still allows you to drive on the freeway.

 

4.27's were a rare, but now popular and desirable factory option. If you aren't planning on running highways much, the 4.27 would be great on the trails.

I know with 3.73's and 33" tires on my Jeep the crawl gear was not crawl-y enough for my tastes. Lots of clutch work. 3.73's to 4.10's is not a big jump.

 

I had two of these Jeeps in the day, one with 4.27s (1st) and one with 3.73s (2nd). I regretted going with the 3.73s ... but there's a lot that I regret about that Jeep.

In your case, I would keep the 3.73 axle gears (which I presume you have) because you had previously asked about "modern" transmission swaps with an overdrive gear. The 3.73s will be better on the highway. Then I'd fit a truck 4-speed to get the low trail gears that people want when they go to lower (higher numeric) axle ratios. IMO these V8 Jeeps don't need any help on the highway, wrt gearing - so a change in gears is entirely for better trail performance. Read the Novak pages about the T18/T19 and the NP435. You have two sets of ratios to pick from with the T18 and three with the T19. The T19 is also full-synchro, having a synchromesh on 1st gear. Any of these transmissions would increase the value of your Jeep, and make it more appealing to a larger pools of buyers (heaven forbid, but life happens).

http://www.novak-adapt.com/knowledge/t18_t19.htm - lots of good info on the Novak site - I suggest a lengthy browse, and you'll keep going back for reference.

<comment> I don't think the '72-75 optional 4.27s would qualify as "rare" - I'd guess that more than a quarter of the CJ Jeeps in this era were sold with 4.27s. But the 3.73s are more common, unfortunately.

 

Gear calculator.

http://www.grimmjeeper.com/gears.html

I’ve found it to be a very useful tool.

 

Using this Gearing Calculator I punched in the numbers from your combination and get a rather sickly 25:1 Crawl Ratio. Axle gearing by itself isn’t going to help that much, I used your same combination with 5.38 gears and only get a 33:1 Crawl Ratio which isn’t much of an improvement.
Therefore I think your best bet is to keep the gears you’ve got and source a truck transmission with a compound low first gear just like Tim said.

 

X2!

We went through this question years ago with our '74. We stuck with the 3.73's and did the Ford T-18. Very happy with it! Made wheeling a whole new, and much more fun, experience! Giggled the whole day on that first trip out with a granny box!

 

As others had said you'll get more bang for your buck with a granny box. The farther forward in your drive train you have the low gears, the more they are multiplied through the other components.

Simple calculation to figure it all out:
Tranny 1st gear ratio X transfer case reduction X axle gears = gear reduction.

I'm a fan of 3.73's with a truck 4 speed, as you get good street drive ability and good gear reduction off road.

 

Right, this is also the “Crawl Ratio” I was talking about earlier.
Just for an example I’ll use my Jeep, since it’s easy for me to explain and I went through the same thing you’re going through.
When I got it the transmission was a Borg Warner T-10 out of the same Corvette the327 came out of. The T-10 is a great hotrod transmission with close ratio gearing and a short shifter throw but sucked for off road because of the too tall to crawl ~2.64:1 first. Coupled with a Dana 18 and 4.27 gears that made for a Crawl Ratio of 27.7:1, in other words just about where you are.
I replaced the T-10 with an SM420 and discovered a completely different Jeep. Now that the compound low first gives me a ratio of 7.08:1 my Crawl Ratio is 74.4:1, all other things remaining the same. The difference off road is amazing, now instead of constantly slipping or riding the clutch I can take my foot off the clutch completely and use the throttle and brakes to control my progress up a trail. Much easier to drive, and I don’t leave the trail reeking of burnt clutch.

 

what about the 3.73's and a tera low kit for your t case. I would think it would be cheaper than regearing or the hassle of a tranny swap. that way you would have good highway manners and good craw ratio.

 

That's probably the easiest path to gear reduction. More effective then re gearing the axles and not quite as effective as a granny box swap, and a whole lot easier than either of the other 2 methods

The T-15 / stock d20 / 3.73 combination gives a crawl ratio of approx 22:1,
T-15 / terra low / 3.73 approx 35:1 and
T-18 6.32 1st / stock d20 / 3.73 approx 47:1.

IMO where the Terra low's really shine in gear reduction is in combination with a granny box to yield a crawl ratio in the neighborhood of 74:1 with the T-18 6.32 1st gear.

 

The tera low's are awesome. I've got them, and its been the best upgrade I've made.

BUT the OP stated he was adding an E-locker, so the rear will be apart anyway.

 

Yep, Tera low's are definitely on my list of to do's.

Ah, yes, the OP. But there is the added expense of re gearing the front to match. Which is why I say to go with another gear reduction method.

 

Ok I'll chime in FWIW. My 75 has an NP435, Dana 20 w/Teralow's and 3.73's. I put a T18 in 19 years ago and ran it for a year before finding the 435. Personally I like the 435 better as it has a lower 1st gear (6.69 vs the T18 6.32) plus the 2nd gear is lower (3.34 vs 3.09). Every little bit adds up. With this combo I can run 65-70 mph all day long but on the
trail I have nearly an 80 to 1 crawl ratio. I ran Trutracs until they quit making them then went 32" BFG's. The only downside to the 435 as opposed to the T18 is the transfer case adapter is a little longer but the 435 is an inch shorter than the T18 so that helps. Have ran this combo since the Teralow's came out for the Dana20 and love it. It is a true dual purpose rig which for me is what I was shooting for.
Hope this helps, keep us posted...

Sgogpn,
Mike

 

I've been looking at the 435 and ford t19 and doing some research on the measurements with the adapters.

The T19 with the adapter for a d20 is 12.9" long.
The NP435 w/ adapter is 14.2" long.

The t19 is 17.5" tall, and the NP435 I read somewhere is 17" tall

I bring up height because I also read about having to drop the trans x-member to fit the 435 in. Was that necessary for your build? I havent heard of anybody having to drop the x-member for the t18/19.

Also what length rear driveshaft did you use dor the 435?

 

I already had my cross member dropped to correct for a 2.5 inch lift. The t18 just happened to fit with out any additional drop. It completely fills the area from the cross member all the way up to the bottom of the tub. The truck 4 speeds are quite a bit taller that the 3 speeds. Depending how much space you have between the tub and tranny, it's possible you may have to adjust the cross member accordingly. I did have to move the cross member back a couple of inches to accommodate the new tranny mount position.

Sent from my LS670 using Tapatalk

 

The CJ-5s from this era with the factory T-18 use a different, taller floor panel. Typically you have to do something to the floors to make any of the truck 4-speeds fit.

 

Isn't it close to $1,000 to do the Tera Low conversion. Probably not much less to put in a truck 4 speed. I spent nearly that to put a Ford T18 in my Jeep. Re-gearing axles will probably be right in there as well.