NH Dana 20 low gears 3.15. Atlas?

[4lofun]

City: Concord

Been out playing in the rocks and although I have 456 gears on 35-in tires I am going to need lower gears in the transfer case for a slower crawl.
I am unable to find any of the low gears. I believe they probably have been stopped being produced.
So I am looking for a transfer case that may already have the gears in it or a set of the gears.
I'm also considering buying an atlas preferably used or I may have to go with a new one so that research has begun as to which gears to buy for that.
Let me know if anyone has a Dana 20 with the low gear set in it or an atlas for sale

 

[bigmuddy]

What tranny are you running, C-4?

 

[Yeller]

I’ve never been fortunate enough to find the correct atlas used. I also believe you are correct about the 3:15 Dana 20 gears. Your transmission and transmission will dictate which gears are most desirable and also your driving style and wheeling locations. To really help pick we need to know what transmission and engine you are running. I feel for the best of all compromises that 1st gear in low with an automatic the overall crawl ratio needs to be between 40:1 and 50:1. With a manual between 70:1 and 80:1.

As an example a C4 has a first gear of 2.461 multiply that by say a 3.8:1 Atlas and your 4.56:1 axle gears and your at 42.63:1. In my opinion that is just about perfect. Gives control, wheel speed when needed, and keeps the engine and transmission happy. Also an important consideration is you can stop it at an idle without shifting to neutral, once you get past 50:1 that becomes difficult to impossible.

Same scenario with a 4R70W. 2.84:1 first gear, Atlas 3.0:1, diff at 4.56:1 equals 38.86, just barely below the 40:1 base line, but close enough, go to a 3.8:1 Atlas and it jumps to 49.21:1 which depending on the engine and your driving style, either works great, with a stock low compression 302, the 3.8 would be my choice. With a healthy 302, 347, 351, or 408 (or desire to go there) the 3.0 would be my choice.

More Horse Power and Torque need less gear to perform well. As an example, I used to work on a King of the Hammers car, it had 500hp/500ftlbs at 34:1 it felt too low, when we first built it it was at 40:1 and was too low. We always felt 28:1 to 30:1 would have been perfect for that car. All of my personal cars are 35:1 to 45:1 and most know the dumb stuff I do lol.

 

[4lofun]

Thanks for the detailed information..
I do have a c4, 2500 stall ( great for the street) big electric fan transmission cooler for the trail.
350 HP, 238hp Dyno to the ground, it's a fuel injected 5.0. cammed, trick flow cam, heads, intake, roller rockers.
Mostly just class six roads up here in New Hampshire. A few rocks and hill climbs. I just feel like I could use lower gearing to go at a slower speed.

 

[tasker]

WHO ARE YOU???

 

[bigmuddy]

Thanks for the detailed information..
I do have a c4, 2500 stall ( great for the street) big electric fan transmission cooler for the trail.
350 HP, 238hp Dyno to the ground, it's a fuel injected 5.0. cammed, trick flow cam, heads, intake, roller rockers.
Mostly just class six roads up here in New Hampshire. A few rocks and hill climbs. I just feel like I could use lower gearing to go at a slower speed.

The reason I ask is that I used to run a very similar combo but ran the ZF manual tranny and with that low first gear and the D20 it was plenty low. Recently swapped to a 4r70w and a 3.0 Atlas with a new EFI 351w, so hopefully that will be plenty to play with as well.

 

[4lofun]

WHO ARE YOU???

Lost cause!
Dranged!
4x4 Brat
4lofun
Junk
All of the above
Depends who's asking?

Now back to our regularly scheduled show.

Anyways need lower gears in a transfer case.
350 HP, c4, Dana 20, Currie 9" 4.56 Detroit locker, 31 spline,4 discs , silly long pedal.

What's my current crawl ratio with stock 75 Dana 20¿

Atlas w 42.63% sounds awesome

 

[Yeller]

If my memory is correct of the Dana 20 being 2.46 it is 27.6:1. A 35.3% difference, so just over 1/3 slower.

 

[ntsqd]

As it happens I own a Jeep D20 with those 3.15:1 gears in it, or so I've been told. It's getting replaced with a RHD NP241 in that vehicle. But, I'm a ways away from doing that as it is a whole power-train swap and nothing happens fast in my yard.

You don't mention having one of the 300M D20 output shafts. If you do not have one, then quit thinking about a D20 and go right to an Atlas. By the time you do all of the updates to a D20 you'll have nearly the cost of an Atlas into it, and it won't be as good.

 

[Yeller]

And why I have a few of them in the garage. Today there are 3.

 

[4lofun]

2.46stock d20
3.00 atlas
.54 is a big difference between the two?
I may be missing something?
I also have 2 other D20 around here collecting dust..
It's a stock D20 just resealed and painted.. No updated output shaft

Ah I would need the 3.8atlas. That's what I was missing

 

[Yeller]

the cost of the output shaft, gears and time are why my go to is typically atlas, even if everything else is brand new. Last year I needed to rebuild and repair a transfer case, my cost on the parts was $2300. I didn't even look at it again, just ordered an atlas and installed it, took a few less hours and needed some driveshaft work to fit but I won't have to work on it again as long as I do maintenance and change the oil in it every 10k after the initial 500 mile break in change.

 

[Ol'Blue]

This Atlas set up for c4/5.0 is in the parts section, but ratios not listed. Maybe a long shot if you havent checked this one out already. Good luck!

https://classicbroncos.com/forums/t...t-case-flares-steering-parts-and-more.325574/

 

[4lofun]

Hey thank you.
Sent a message. So we see. It says 5.0? Hope that's not the ratio, I would need 40 inch tires...
I want the rear bumper as well..

 

[Ol'Blue]

Hey thank you.
Sent a message. So we see. It says 5.0? Hope that's not the ratio, I would need 40 inch tires...
I want the rear bumper as well..

Finger crossed for you man!

 

[Yeller]

5.0 is the ratio, if it had been 3.0 maybe even 3.8 I’d own it already, have something it would fit in.

IMO the only use for a 5.0 requires a 4cyl with a turbo or super charger in the back seat, portal axles, 4 wheel steer and 42” sticky tires. Oh and a power glide transmission

Something like this
Pretty Penny

 

[Ol'Blue]

5.0 is the ratio, if it had been 3.0 maybe even 3.8 I’d own it already, have something it would fit in

Bummer

 

[ntsqd]

Looking back up I see that you have a C4. With an auto trans there's a variable torque multiplication in the converter that isn't always considered. I've not found hard numbers for this "ratio", but I can report that I've been told by a racing converter builder that 2.25:1 to 2.5:1 is pretty safe. Those GMC FWD RV's from the 70's had a stock converter in them with a 2.6:1 "ratio" and I was told that those are a very rare and unusual converter with an unusually high "ratio." Keep in mind that this only happens under the stall speed of the converter and tapers off as you approach stall speed. After it stalls the "ratio" is about 1.005:1 or so. At least, that is my understanding of the topic anyway. I've been wrong before.
I've always used 2.5:1 in my calculations, even if it might be a tiny bit optimistic.