FJ40 Drivetrain Options/ Final Drive Ratio For 37s? (1 Viewer)

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I would actually like to run an 80 front if I can, but I would need to sell my 40 axles first and I'm not sure I'll find someone willing to pay what I have into them for parts in a timely manner. But we'll see. And no, I don't expect nor would I want to do 81 in a 40 with a 2F on 37s... lol. Just comparing gearing.

40's drive pretty well at speed with a stretched wheelbase, even a few inches makes a big difference.

I ran an NV4500, toybox, splitcase for a while and the compound low was great. I was around 156:1. Didn't use it much, but it was nice for some stuff.
 
40's drive pretty well at speed with a stretched wheelbase, even a few inches makes a big difference.

I am stretched to 102" and yes, drives awesome at 95. :) I sent @sogncab a video last year. Not a stock motor... lol.

I sent you a message @Drcrane I have a Blackbox I removed if you decide to go that route. Save you some money over a new one.
 
I am stretched to 102" and yes, drives awesome at 95. :) I sent @sogncab a video last year. Not a stock motor... lol.

I sent you a message @Drcrane I have a Blackbox I removed if you decide to go that route. Save you some money over a new one.No way
No way... PM'ed....
 
I am stretched to 102" and yes, drives awesome at 95. :) I sent @sogncab a video last year. Not a stock motor... lol.

I sent you a message @Drcrane I have a Blackbox I removed if you decide to go that route. Save you some money over a new one.

Lmao, I've gotten mine up to about 100 mph, 100" wheelbase lol. Also not a stock motor.
 
I am stretched to 102" and yes, drives awesome at 95. :) I sent @sogncab a video last year. Not a stock motor... lol.

You have the 2.8 jeep diesel currently, correct?
 
The 2.8l's auto trans was the same length as the NV3550 with the black box that I took out. So I didn't have to do anything with my driveshafts or my transmission cross member when I did my motor/trans swap again...lol.

That is why I took out the black box @Drcrane
 
I struggle with this myself. I have a pretty capable rig, but then I go on wheeling trips and I want more, more, more …how far do I take my 40? Do I stretch it for the mythical perfect wheelbase? Tons? Links?

I bought it to have a classic truck I loved. I built it to handle the road(70) and crawling- to the best of my abilities. I also live in an area that doesn’t have a ton crawling to be had, but I enjoy driving it until the magchloride comes back around.

The more trips I go on, I’m not sure I want a bodied rig for crawling. I want that low slung jungle gym on 40’s that says no fear of damage. And I want to build it. Can I have both? Not right now, I have another project in the works. Future? A boy can dream. Can I turn my forty into that vehicle? Possibly, but I may be too deep to justify it.

Why do I write this: as a cautionary tale. The 40 is a beautiful, rough cut beast. Can you build one for your rock crawling dreams? Sure, many have. A lot of them have posted here. However if you’re like me, eventually you realize that it might not be the be the best tool for the job.
 
I struggle with this myself. I have a pretty capable rig, but then I go on wheeling trips and I want more, more, more …how far do I take my 40? Do I stretch it for the mythical perfect wheelbase? Tons? Links?

I bought it to have a classic truck I loved. I built it to handle the road(70) and crawling- to the best of my abilities. I also live in an area that doesn’t have a ton crawling to be had, but I enjoy driving it until the magchloride comes back around.

The more trips I go on, I’m not sure I want a bodied rig for crawling. I want that low slung jungle gym on 40’s that says no fear of damage. And I want to build it. Can I have both? Not right now, I have another project in the works. Future? A boy can dream. Can I turn my forty into that vehicle? Possibly, but I may be too deep to justify it.

Why do I write this: as a cautionary tale. The 40 is a beautiful, rough cut beast. Can you build one for your rock crawling dreams? Sure, many have. A lot of them have posted here. However if you’re like me, eventually you realize that it might not be the be the best tool for the job.

It's a pretty blurred line for sure. 8+ trails are about the limit for my 40 that I will go on, I like to body too much. I too want the legendary jungle gym lmao.
 
It's a pretty blurred line for sure. 8+ trails are about the limit for my 40 that I will go on, I like to body too much. I too want the legendary jungle gym lmao.
The trip to sand hollow last month sent my buddy looking for buggy to buy. We were on trails that were as far as I’d want to take a nice-ish bodied rig. We could see buggies playing and it looked fun. The buddy in question has more money than me to play with, so he’ll probably get one eventually. That will eventually pull me in to one I’m sure- I wanna play too.

We also had a jk on forties in the group, he took it on lines that I wouldn’t put that much money on. Super ballsy. This does not interest me.
 
I struggle with this myself. I have a pretty capable rig, but then I go on wheeling trips and I want more, more, more …how far do I take my 40? Do I stretch it for the mythical perfect wheelbase? Tons? Links?

I bought it to have a classic truck I loved. I built it to handle the road(70) and crawling- to the best of my abilities. I also live in an area that doesn’t have a ton crawling to be had, but I enjoy driving it until the magchloride comes back around.

The more trips I go on, I’m not sure I want a bodied rig for crawling. I want that low slung jungle gym on 40’s that says no fear of damage. And I want to build it. Can I have both? Not right now, I have another project in the works. Future? A boy can dream. Can I turn my forty into that vehicle? Possibly, but I may be too deep to justify it.

Why do I write this: as a cautionary tale. The 40 is a beautiful, rough cut beast. Can you build one for your rock crawling dreams? Sure, many have. A lot of them have posted here. However if you’re like me, eventually you realize that it might not be the be the best tool for the job.
This was the dilemma that originally led me to wanting a milder 40 build, and then a fake 45 crawler. My body is already 80% custom and thick steel, and would probably only wheel hard with the top off. Should be a tough rig. I would still love to finish the 45 one day, but another rig doesn't make financial sense for me at the moment.
 
You guys got me thinking last night. I have a 79 frame that I stretched to 116" for the 45 build using sections from a bent frame. This frame was in better shape than the one I used in the current 40 build. I also have 3 hard tops and extra tub topper rails. While I may have the bud built quarters welded to the B pillers, I am now tempted to shorten up the stretched frame to something close to an FJ43, stretch the body, and cobble together a stretched hard top. Driveline length won't be an issue then, and I will make use of the better frame. May even be able to sleep in it, something that would be nice for big trips.

20200804_160607.jpg
 
I am in the middle of my 40 build and am considering a change in direction from a more mild build on 33s and going straight to 37s. I had another build planned for big tires, but having thought about this all winter I have decided yet another rig isn't worth all of the money, hours, storage, insurance, etc. just to go up a size or two in tires and would like to just commit to one rig I will be able to enjoy more rather than have one sit most of the year.

I am sticking with my 40 as far as I have taken it, but will be making some changes to axles, drivetrain, and body to get it where I want it, which is a capable wheeler I can drive moderate distance, potentially cross country for big trips out west, and won't be afraid to wheel hard. Part of the equation will be deciding on a drivetrain setup. I want adequate gearing to run 37s (Will not be going bigger) with the 2F and hopefully not feel the need for additional gearing down the road.

That being said, what would a good rock crawling final drive ratio be for running 37s and the ‘ol 2F?

I have listed a number of results calculated using the GrimmJeeper gear ratio calculator for a variety of trans/tcase and black box combinations and approximate cost of parts that I’m sure others with the same dilemma will find useful for comparison. Unfortunately the only doubler option currently being produced for the H42/H55f is the NWF black box. These are all assuming 37s and 4.88 diff gears. (with one bonus 4.10)

Current prices:
NWF BB - $3600
4:1 split case gears for 34mm idler gear split case -$1300
Orion kit-$1950
H55f-$2400

Prices are only considering the above listed parts assuming I already have an H42 and split case. There will obviously be other costs associated with rebuilding a used trans/tcase.

H42 and 4:1 orion ($1950)
Final Drive- 70:1
2500 rpm cruise speed: 56
3000 rpm cruise speed: 68

H42 and 4:1 split case (10% underdrive) ($1300)
Final Drive- 70:1
2500 rpm cruise speed: 51
3000 rpm cruise speed: 62

H42 SS, NWF BB and stock split case ($3600)
Final drive ratios:
L1- 40:1
L2 - 47:1
LL - 108:1
2500 rpm cruise speed: 56
3000 rpm cruise speed: 68

H42 SS, NWF BB and 4:1 split case(10% underdrive) ($4900)
Final drive ratios:
L1- 70:1
L2 - 52:1
LL - 189:1
2500 rpm cruise speed: 51
3000 rpm cruise speed: 62
----------------------------------------------------------------------------------------------------------
[4.10 gears]
H42 SS, NWF BB and 4:1 split case(10% underdrive) ($4900)

Final drive ratios:
L1- 58:1
L2 - 44:1
LL - 159:1
2500 rpm cruise speed: 61
3000 rpm cruise speed: 73
--------------------------------------------------------------------------------------------------------
H55 and 4:1 split case (10% underdrive) ($3700)
Final Drive- 94:1
2500 rpm cruise speed: 60
3000 rpm cruise speed: 72

H55 , NWF BB and 4:1 split case (10% underdrive) ($7300)
Final drive ratios:
L1- 94:1
L2 - 71:1
LL - 257:1
2500 rpm cruise speed: 60
3000 rpm cruise speed: 72

H55 , NWF BB and stock split case ($6000)
Final drive ratios:
L1- 54:1
L2 - 64:1
LL - 146:1
2500 rpm cruise speed: 66
3000 rpm cruise speed: 80

As you can see, I would be struggling on long highway drives with an H42 and 4.88s. Going to the H55 will make a big improvement, even with the 10% reduction of the split case gears eats into that extra gear. However, with 4:10s the H42, BB and 4:1 split case gears option gives a wide range of gear options and good highway speeds, all while sticking with stock 4.10 gears. The 10% underdrive in high range would be about the equivalent of running 4.56s in high range with 4.10s, which would probably be livable on the street with 37s.

I currently have an FJ60 H42 with extension and split case. Having this option now means I can finish out my build using this combo and later add an H55 and 4:1 split case gears and not have to mess with anything. The black box, as cool as it is, is an expensive option and don't think I could make it fit with the H55 without moving the rear axle back quite a bit more than I already have. I could also find a short shaft H42 and potentially fit a black box and go the 4.10 diff gear route.

I am leaning towards the H55 and 4:1 split case option. I would have a 94:1 final drive ratio, good highway speed, and don't need to worry about an oil cooling setup on a black box for highway driving. The question though, will this be low enough or will I feel the need for a doubler when I get into progressively more technical trails down the road? The H42 short shaft, Black box, and 4:1 split case gears option is a close second, if deeper gearing is worth it.


Thoughts?

PFA, on 285/70r17s and FJ60 2" lift springs at the moment.

View attachment 3285966
Are those front fj60 springs or rears. I’m working through fj60 rear springs on the front of my 40 but it looks like I need to relocate my spring hangers.
 
Speaking of 60 springs.... I just took out a newer set of rear 60 OME springs I put in my 40 2 years ago if you need them. I should be setting the rear on coils this weekend.
 
Are those front fj60 springs or rears. I’m working through fj60 rear springs on the front of my 40 but it looks like I need to relocate my spring hangers.
FJ60 fronts in the front, rears in the rear. Front springs are same length as 40 but pin is centered whereas 40 is offset rear, so front is moved forward 1.5". I moved the fixed hanger back to compensate, but this also moves the hanger down, so I am also running longer shackles to compensate. Rear springs are a little longer and shift the axle back about 2.4" (not flipped). My quarters are from Bud Build and I had Bud widen the wheel well to center the wheel and be a better fit for bigger tires.
 
So, an option that you'd not posted.
There is a 3:1 gearset available for the split case that does not affect the high range.

An H55F + 3:1 + 4.88's in the diffs will give you decent legs for 37" tires and get you about 70:1 crawl ration which many think is about perfect (I run about 68:1 with an SM420 and 4 speed single piece t-case, and never feel like I need to go any lower).

This is what I am considering currently for my FJ40, though I am still waffling between keeping the 2F with a sniper or going to a 1HD-FT diesel. If I did that I'd probably go back to 4.11 or 3.73s in the diff.
 

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