Auto Crawl Ratio Advice (1 Viewer)

[70CRZR]

I know a few on here have autos, and I want to get some advice on a T-case. I am currently running 36" tires with a SM465/NP205 , Dana 44 and Eaton Rear w/4.10 r&p. My current crawl ratio is about 53:1. It does pretty good, but there are some occassions when a little lower would be nice.

I just got a 700R4 to rebuild, but I am not sure what I should do with the transer case. I don't really want to change the R&P, I like the 4:10s. Will I be ok with a NP241, that would put me around 34:1, or should I go Atlas 4.3 making it 53:1 ? To me, the Atlas may be too low. If the NP241 is not going to be low enough, should I bite the bullet and try to find 4:56 gears for the Eaton ? That would put me close to 38:1.

 

[woody]

I run a 700R4 with a 4:1 Dana 300 behind it and 4.1's in the Toyota diffs.....LOVE it. There are rare times I'd like to be slower, but I have never had an instance where I wished for 2.6's t-case gears.

Changed over from a SM465/cruiser case and the auto is great.

Have about $1000 in the trans, run a stock HD stall converter, and the D300 has about $1500 in it with 32-spline front and rear shafts and the 4:1 kit.

 

[70CRZR]

Thanks Woody. I thought the Atlas would be too low, good to know 4:1 works good. I would rather be a little deeper than not having enough.

If I can find the extra money, maybe I will spring for a Stak 3spd or Atlas 4sp case.

 

[freds40]

Another option is the Lomax 205. Cheap and super stout. I ran this behind a TH400 and 5.38s in my 40 on 42s and it worked awesome. I had a 2k TCI "truck" converter that let the rig stop no problem but would wind up great.

I liked the Lomax because a donor 205 is roughly %100 and the Lomax at the time was right @ $1K. Can't beat that price for a geared case with 32 spline front and rear outputs.

 

[70CRZR]

That's a good option too, especially since I already have a 205. The only problem I see is that the NP241 is 2.72, and I would not be gaining very much going 3.1. I should be able to source a 241 for nothing or very little, versus the $1K for the Lomax. I would also have to mess with mounting the 205 on the 700R4.

 

[Tapage]

the question is .. what kind of off road you do .. coz I don't really feel that 53:1 it's too low .. I'm close to 69:1 and I feel it's fine for mud .. and that's why I ask ..

 

[70CRZR]

A little bit of everything. Since I really don't have the money for a multispeed case, I wanted to make sure I could crawl but still have a little wheel speed. I don't get hardcore in the rocks, but I keep trying more difficult lines everytime I go out.

 

[Eskimo]

I was at 59:1 with 38.5's, and felt it was too much except for extremely technical rocks.. I usually started out in 2nd, which was about 33:1 for general trail running. 1st didn't give me much wheel speed at all...

Now I'm at 40:1 with 42's and think it's lacking just a little in the very slow stuff, but I have a very good cooler, and just 2-foot it.. I certainly don't have to bring it to stall to climb any rocks though. With 36's I think it would be ideal. (I'm assuming you have a v8 by the way)

I will likely be doing a lomax 3:1 in my NP205 in the future, but mostly because I can't leave well enough alone and it'll help get the engine into the powerband more quickly, and can always rip into 2nd if I need wheel speed.

 

[70CRZR]

Thanks Eskimo, yeah I am running a 350 V8. If I can find some 4:56 gears for my Eaton, I will go with the NP241, which will put me close to 40:1. I would swap it out for a 14 bolt, but it is already locked and has disc brakes.

 

[rapovt]

I am thinking about going auto, not surewhetrher 700r4 or t400
will have TPI 305 with cam 36 irocs, 100" wheelbase, soa front, linked rear, wheeling in the east
currently hf42, 3.55-toybox,2.28, 3speed transfer,2.28-4.11 rp=75.8 could be just a hare slower in the rocks, use mostly 2,3,4 with the toybox on trails

t400 2.44-2.28-4.11=23 or 2.28 for the toybox=52.1
700r4 3.06-2.28-4.11=28.7 or 2.28 for the toybox=65.3

Woody- yours figures out to be 50-1, what size tires? do you ever want lower?

 

[green40]

I am thinking about going auto, not surewhetrher 700r4 or t400
will have TPI 305 with cam 36 irocs, 100" wheelbase, soa front, linked rear, wheeling in the east
currently hf42, 3.55-toybox,2.28, 3speed transfer,2.28-4.11 rp=75.8 could be just a hare slower in the rocks, use mostly 2,3,4 with the toybox on trails

t400 2.44-2.28-4.11=23 or 2.28 for the toybox=52.1
700r4 3.06-2.28-4.11=28.7 or 2.28 for the toybox=65.3

Woody- yours figures out to be 50-1, what size tires? do you ever want lower?

Gary, doing the engine this winter?

 

[woody]

the 700r gives you two advantages.....deeper first gear AND overdrive....I'm amazed at the number of times I pop into overdrive between trails

37's on my rig right now...orangefj45 created my build list/recommendations for the tranny and my builder added a few minor things (like a 5-pinion planetary)....ended up right around $1k with labor....the tranny works PERFECT...at a 600ish rpm idle, it just barely starts to creep with no brake....come to an obstacle and a gentle throttle gets it crawling....easy to control, a breeze to drive.

A few folks have driven the rig over the past years...ALL have been impressed with how easy it is to handle, and it's 'point and shoot' capabilities.

luck I tell ya, all luck....

 

[Gumby]

I have the TH400 only because I wanted to do the 203/16 spline doubler. The 400 came with the 203 so it was easy.

The 400 has a slightly higher first, but Woody and I "raced" once for about a 100 years. 2000 RPM in low 1st (low/low 1st for me) and it was pretty darn close. His bigger tires probably made up the difference in first gears.

The 400 is arguably stronger, but not to where you would see it in an under 500 hp rig.

I don't miss OD going from trail to trail too much, but I have the extra set of gears to go 2:1 when Woody might use 4:1 and OD.

The TH400 sucks more power to run it, but again not much of a problem behind a 350 on the trail.

the quick version of all that is a 700R4 would be nicer, but a TH400 is a perfectly acceptable trans

 

[orangefj45]

the 700r gives you two advantages.....deeper first gear AND overdrive....I'm amazed at the number of times I pop into overdrive between trails

37's on my rig right now...orangefj45 created my build list/recommendations for the tranny and my builder added a few minor things (like a 5-pinion planetary)....ended up right around $1k with labor....the tranny works PERFECT...at a 600ish rpm idle, it just barely starts to creep with no brake....come to an obstacle and a gentle throttle gets it crawling....easy to control, a breeze to drive.

A few folks have driven the rig over the past years...ALL have been impressed with how easy it is to handle, and it's 'point and shoot' capabilities.

luck I tell ya, all luck....

i'm stoked to hear you're still happy with the th700. i was very confident that you would be.


ask me, 40:1 is enough with an auto and tires between 33-37" for mild to medium wheeling. if you're gonna go in the rocks, the opt for the atlas.

for this application, i'd run the 241 with the sye and call it good. quite geartrain, very reliable and easy to find parts for. no expensive adapters required.


if you want lower gearing, i have a new atlas for sale with the 27 spline input for the th700 and the 32 spline front upgrade. overkill for this setup but it's your $s...........

 

[fj40charles]

I'm running a TH400, Atlas 3.8 and 4.88 r/p and 42" tires behind a 350 TBI engine. It provides me with a 42.8x:1 crawl ratio (2.48 x 3.8 x 4.88). I have a low stall (~900 rpm) Allison type RV torque converter.

Works well for a trail rig, but if I were to put some street miles on it, then I'd consider a TH700 or lower r/p gears.

 

[warpdriv]

I love by 700r4/np203/3sptc (3 speed transfer stock case). The 2:1 in the np203 helps find the right gear. I usually run the 203 in low and my 3sp in hi. Stupid low (1st/low/low) is fun on the rocks. A couple things I did was to keep the 700r4 stock because it will help absorb the shock in the drive line when your tires are spinning and they suddenly get traction. Also I built a bracket between the cross member on the mount on the 700r4 and the np203. The 700r4 only has 4 bolt holes in an aluminum case. They will strip out because of frame flex.

To help fit all that in, I flipped my springs and my rear spring hangers. It moved my rear axle back 7". So I only had to cut my read DS 1".

Hope this helps and good luck.