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Newbie Gear Reduction + Rocklobster Questions

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04 Apr 2019 22:00 #205550 by deathwobble
Hello new to this so sorry if this has been covered before. I have tried my best to search for it in the search bar.

I have just purchased a 2002 jimny with a manual transfer box. I have plans to go 235/75r15. I understand this is going to arise some issues with the jimny stock gearing.

I am aware that there are two options, rocklobster or a gear change. I am hesitant to change the stock gears as there is multiple complaints on here of the chains wearing and slipping. Although researching to see how much replacement chains cost all the chains online say electric transfer box. Does the manual transfer have a chain/suffer from the same problem?

Secondly regarding the rocklobster. There are very few sj410 and 413s where i live (n.ireland) so i am considering buying one from rockwatt engineering. Does the rocklobster and 235/75r15 combination leave the high range still driveable on the road as i only use the jimny for offroad events but i would like to be able to drive to these events.

Thanks

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04 Apr 2019 22:17 #205552 by jackonlyjack
YES it will be fine :)
Just to say you will need different prop shafts and a cradle to fit it ;)
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05 Apr 2019 16:50 #205572 by Riccy
I used to run 235's with a 4.16 lobster box (1.5 in high). Ran well, but was revving a bit high on the motorway. Shouldn't be an issue for you there. Excellent in low box as well. Much lower than standard.

Another option is to consider swapping the diffs to the later VVT jimny ones, which a 4.3 instead of the earlier 3.909. This is probably much cheaper than a rocklobster box.

Numbers for whats what in different years of jimny are in the wiki, put them into grimjeeper website and see what result you get.

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R7me gbox & 5.16 Rocklobster, 285 75 r16 Toyo MT, 2x ARB Lockd' diffs, 7" lift, Recaro's, Custom bar, arches & guards, Snorkel, K&N, Winch, CB, etc, etc

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05 Apr 2019 22:25 #205584 by deathwobble
Thanks for the reply I just came across posts about changing the diffs today. Is it a straight swap changing the crown and pinion or is there other parts required. I couldn't find in much in the way of carrying out the swap.

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06 Apr 2019 06:38 #205593 by Riccy
Even easier than that playing with the crown & pinion, you just unbolt the prop and take the whole unit out from the axle housing, then bolt a different one in.

Minor grinding of the axle casing is needed to fit the crown wheel in, maybe a couple of mm off the hole it fits into.

Obviously the half shafts need pulled and oil drained, but its a lot easier than the landrover style where its a sort of lid on the non driveshaft side of the axle.

Finally bear in mind that if you were to go to larger tyres in the future then you would be forced into the rocklobster route, meaning the diffs would be to swap back again.

J999 MNY, M16 VVT
R7me gbox & 5.16 Rocklobster, 285 75 r16 Toyo MT, 2x ARB Lockd' diffs, 7" lift, Recaro's, Custom bar, arches & guards, Snorkel, K&N, Winch, CB, etc, etc

SL06 ULS ULYSSES
06' pickup tipper project

www.youtube.com/user/riclemus
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06 Apr 2019 07:00 #205594 by kirkynut
A diff swap will not reduce the gearing as much as a Rocklobster doors or as much as a Trail Gear gearset in your Jimny transfer box.

Rocklobsters are noisy because they have new gears put in, which run on old gears, which causes a whine. I was on the understanding that Trail Gear gearsets overcome this but a recent post from the owner of a Trail Gear gearset in their Jimny said they too are a little noisy.

A Rocklobster mounts with a bolt through the chassis outriggers and the cradle it sits in with poly or rubber bushes between. This causes vibration and noise through the car from the transmission as that bolt touches the chassis and the transfer box on its way through them, effectively making a mechanical join or link.

The Trail Gear gearset could be used with standard Jimny transfer box mounts that are rubber bonded, so dampen the noise and vibration greatly, however the torque will tear those rubber mounts apart and you'll end up using the bolt through mount in the end anyway.

If it's an off road toy the noise on the road is unlikely to be an issue as you don't have to listen to it daily.

I wouldn't do this if it's your daily ride though. I'd consider the diff change option but accept it's not anywhere as good as a Rocklobster off road and your clutch will still take a battering off road.

Kirkynut

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