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31s and transfer case upgrade

  • Jimima
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07 Feb 2023 19:17 #247419 by Jimima
31s and transfer case upgrade was created by Jimima
Hi guys
new to the forum but long time follower. Im seeking clarity on replacing the chain drive/push button transfer case in aid of allowing bigger tyres, probably 31s, and lower low ratio gearing. Jimny is used 99% off-road and only sees the tarmac on its way to local 4x4 trips and sometimes when our daily’s are having services etc. I know this subject has been done to death but cant find all the info i need in one place.
As I understand you get a sj413 transfer case and some of the shafts, tear it down and reassemble it with the new mounting bracket and a trail gear lobster kit.
my jimnys a 2014 m13a manual currently with Maxxis mudder 753 215/75-15 muds
ROH 15x7 black trac steel 0 offset
Dobisons 2 inch lift
Dobisons castor correction 
Tough dog steering damper 
Zukparts rear shock relocation brackets
ARB diff breather kit
Zukparts transfer case mounts
Zukparts transfer case armour plate
Zukparts radius arm protection 
ARB onboard air compressor 
Optima yellow top battery 
Custom snorkel/airbox
runva 9500 winch and homemade winch plate 

 
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  • Lambert
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07 Feb 2023 20:27 #247425 by Lambert
If you look in the information section on the top banner there's a list of all the various ratios used in the various models and markets. Basically you have 1 to 1 high at the moment and will benefit from 1.3 to 1 for 31s. This either means finding a push button case out of an automatic or fitting an earlier lever action box. That or as you suggested finding an SJ box and doing a mini lobster.

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
ADOS Attention Deficit Ooooh Shiny!

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08 Feb 2023 01:28 #247432 by Jimima
Replied by Jimima on topic 31s and transfer case upgrade
Thanks Lambert, i want to move away from the chain drive transfer. When you say an sj box do you mean a 410 or 413 and a “mini lobster “ is just a swap of transfer of the box without changing any internals?

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08 Feb 2023 04:19 #247433 by Lambert
That's correct, yes.

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
ADOS Attention Deficit Ooooh Shiny!

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08 Feb 2023 08:28 - 08 Feb 2023 09:23 #247435 by yakuza
For me doing much more than 1% on road I found that the total build process and what revs I ended up with did not make a SJ lobster case a good alternative. The gears are very different on the 2005 and newer compared to the older Jimnny.
I used the grimjeeper online gearing calculator to see what revs I would get at various gearing alternatives and different tire sizes. i did not plan to go to 31" but 29 or 30 maybe sometime but still. and the amount of building needed with making a driveshaft and the cradle and mounts and most likely also change the axle gearing, it was too much work. And I even got the SJ case and the drive shafts in my garage.
I changed the gears in my original case. But that said, the noise from the chain does bother me a bit.

For me on 235's that is, driving 8-10 hours to get to the offroad sites :dry:

Still I would recommend anyone doing tire or gears to check the figures thoroughly to avoid coming out with a bad result.

www.grimmjeeper.com/gears.html

put all your own data in there and see. :)

Norway 2005 Jimny M16A VVT, 235 BFG MT, 2" Trailmaster, ARB rear lck, 17%/87% high/low gears.
Last edit: 08 Feb 2023 09:23 by yakuza.

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08 Feb 2023 09:35 #247436 by jackonlyjack
I'm sure if you swap R72 gearbox for an R7ME 
Then fit sj 410 transfer you will be good for 31's/32's

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  • Jimima
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09 Feb 2023 04:52 #247457 by Jimima
Replied by Jimima on topic 31s and transfer case upgrade
I had a play on the Jeepers creepers page but can’t really tell how it helps me. I just want to know if i put a samurai tranfer case with a trail gear 4.19 gear kit in it and slap a set of aggressive 31s on if I’ll still be able to climb steep hills or if I will be able to do it better than standard on the 215/75s or if I’ll create an unworkable loss in torque.

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09 Feb 2023 08:37 #247459 by sniper
The VVT gearbox (R72) doesn't match the ratio's for the chain or sj transfer boxes, I'm no mathematician and can't explain the gearing but I have seen others do it and be unhappy.

To put a VVT (4.3 diffs) car on 32's and have a useable low range, you need to change the gearbox to the pre VVT (R7ME) gearbox. Standard chain drive transfer box and away you go. I run this set up with 30's and its under geared, wants 31's / 32's.

Fitting an SJ transfer box or lobster would want pre VVT (3.9) diffs. I have a lot of friends with this combo and they are very happy.

sniper

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