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T case gearing for 40s

dirtybird

Red Skull Member
Joined
May 19, 2020
Member Number
287
Messages
143
Loc
Mayetta, KS
I'm currently building a fj40 buggy. I have a questions on t case gearing. Running built tons spooled with 4.56 gears. Tires are 40" trep stickies. TBI 350 TH400. I was going to do a 203 205 doubler but the length is going to kill me. What would be the sweet spot for low range gearing? I figure I will just order an Atlas at this point but not sure what ratio to go with. Mostly will be midwest wheeling but plan to go out west to moab and hammers in the next couple of years. Any recommendations on T case gearing? Pic of what I'm starting with.
20230904_151353.jpg
 
The dana 300 integrated eco box cases are short and easy to package. Could also do the 205 the same way. Just gotta wait a little if you're ordering one today.
 
Elaborate on 'tons'. Are you limited to 5.38, or able to go 7.17.

As you sit with 40s and 4.56s, you are effectively worse than a stock vehicle. Minimum 4.3 if you plan to do any crawling and not burn up the TC/trans.
 
Yeah, I figured I am going to have to regear the axles. So 5.38s and and 3.8 be the sweet spot? What is the length of the 300 ecobox? Front axle is driver side drop so I'd have to flip a 300. Just running the numbers I will be money ahead just going atlas. I'm not seeing any way to do a doubler without have close to 2k in it. I have the th400 32spl 203 and ford 205 sitting here but with front axle placement the front will definitely need a carrier bearing,
 
TRINDU said:
Elaborate on 'tons'. Are you limited to 5.38, or able to go 7.17.

As you sit with 40s and 4.56s, you are effectively worse than a stock vehicle. Minimum 4.3 if you plan to do any crawling and not burn up the TC/trans.
Click to expand...
Ford hp d60 and 14 bolt.
 
Have you looked in the LT230 version ?

they have a 3.2 low range. and depends on model you buy a 1.0-1.2-1.4-1.6 high range.

I have 5.38 in the axle and i drive almost everything in 1.6 high range with th400 and a 41 tyre

Only downside off the lt230 is the output is offset and thats not ideal with my 14 bolt
 
Short rear shaft length is my biggest concern at the moment, just some rough measuring puts the rear yoke less than 36 inches from rear axle centerline with the 203 205.
 
My rear shaft is 28" on my buggy and there is 25" of suspension travel without any issues.

That said the angle is way better than what you're showing here.
 
Bebop said:
My rear shaft is 28" on my buggy and there is 25" of suspension travel without any issues.

That said the angle is way better than what you're showing here.
Click to expand...
I need to get the rear axle sitting under it and check for sure yoke to yoke. Do you still have that atlas for sale?
 
Seems to vary by region

My buddy did the exact gearing combo you are at with a 5.3 and said it wasn't low enough. Back east guys seem to run a little higher gearing since creepy crawling doesn't usually get you anywhere.

If it were me, I'd probably run what you have and see how it is, but if it's not working out length wise, lile someone mentioned, maybe look into the ecobox I. That will net you 2/2.7/5.4:1

Problem with just going 4.3 atlas is that for one, it's not that much lower, and 2, you're stuck with 1 range vs 2.
 
First a disclaimer because this subject is always subjective. People get away with ratios I can’t stand. For the wheeling I do, 40’s 5.13’s/5.38’s and 4:1 or 4.3:1 is my t-case sweet spot.

That is accounting for 300 ish average flywheel hp and an automatic with a normal torque converter. My crawler has true 40’s 5.13’s in the axles and a 4.3 atlas but my first gear in the auto is lower than 1st in a Th400.

I also like a 700R4 which has a way lower 1st gear with 4.3:1 case 5:38’s in the axles and 40’s. YMMV.
 
JR4X said:
First a disclaimer because this subject is always subjective. People get away with ratios I can’t stand. For the wheeling I do, 40’s 5.13’s/5.38’s and 4:1 or 4.3:1 is my t-case sweet spot.

That is accounting for 300 ish average flywheel hp and an automatic with a normal torque converter. My crawler has true 40’s 5.13’s in the axles and a 4.3 atlas but my first gear in the auto is lower than 1st in a Th400.

I also like a 700R4 which has a way lower 1st gear with 4.3:1 case 5:38’s in the axles and 40’s. YMMV.
Click to expand...
IDK how you deal with that.
I have 300hp, 3:1 case and 5,13 with 43s and find it almost too low of a ratio.

I know, the wheeling types are very different.

dirtybird said:
I need to get the rear axle sitting under it and check for sure yoke to yoke. Do you still have that atlas for sale?
Click to expand...
Yes. But have an interested party
 
Bebop said:
IDK how you deal with that.
I have 300hp, 3:1 case and 5,13 with 43s and find it almost too low of a ratio.

I know, the wheeling types are very different.


Yes. But have an interested party
Click to expand...
Traction: I need wheel control not wheel speed. Most of the time. But it will zing the wheels as fast as I need it when I need it.
 
Since we're on the subject.....anyone want to comment on gearing for a 4cyl/auto?

Normally I'd say some sort of doubler would be almost necessary but I already have a 3.8 atlas with the right input and mounting face for the aw4 ill run, and 60s with 6.17s, this comes out to almost identical to 4.3/5.38s.

Gearing calculator says like 45 mph top speed in low, which is probably faster than the squirrels will pull anyway.

Only issue would be if low isn't low enough for high traction shit like sand hollow.
 
one buddy has similar set up v8 th350 and 4:1 d300 and 571 gears in the axles. he bitches about its too low for between the trails and always has to move to high side going from hard spot to hard spot. but that could be just him... if only one case i look at something with 2:72 to one...
 
Sounds like I may just put lower gears in the axles and just run the 205 as it sits and wheel it some to see how I like it before spending big bucks on a t case.
 
I would say for the OP.
5.13 in the axles and a 3.0 or 4. 1 tcase.
241/205 doubler is my first choice
3.8 Atlas
4.1 D300
2.62 D300
 
So what is the junkyard setup to mate the ford 205 to the 400? NP208 adapter notched for the shift rail? I have a long 32 spline input if that's what I need.
 
5.38 gears to me is standard operation when mounting 42" ish tires. Lower if possible depending on HP.

Have to remember that you need high range torque also. For example, when you jump out on the back roads of Tennessee that are equally steep, you'll be working hard with 4.10s high range.

Don't want to stop to grab low range mid mountain pass
 
I read somewhere that the 6 bolt round pattern was pretty close to the ford 205 round pattern.
 
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