Help me gear is...

Hey gang,

Well as it turn's out my gear box is completely stuffed and i need a new one. I have 2 options here ( it think)

A) Install a non-vvt gear box which is a bit stronger than a vvt box and install a sierra t-case later down the track
b)Install a vvt box and risk the gear box breaking again.

I would like to do option A...but i don't know what the final drive ratio is going to be.

So here's where i would like some help,

With the current setup i have 4.3 diff's ratio's, a vvt transfer case with trail jimny 20% gear's and a vvt gear box. With that setup i am about 4-5% over geared with the 31's which is fine. Also worth noting 5th gear in a vvt jimny has a ratio of 1:1 rather than a over drive gear.

So what i would like to know, what is my rev's going to be at 60MPH (100 KPH) with this setup:

VVT transfer case, 20% reduction gears, 4.3 diffs and a non-vvt gear box?


Current rev's are 4000rpm @ 100 KPH.

Please help if you can!!!

Thanks Andrew

Here is a very useful gear ratio calculator that may help you

www.planet4x4.net/forums/calculator.php

I don't think the non VVT gearbox is a straight swap for the VVT one - the mountings are different and its a different length. However if you go down the route of rocklobster transfer box then the non VVT gearbox would be much better as otherwise you will end up very undergeared with very high engine revs for low speed. You could then change the diffs to earlier 3.9's which helps a bit but still it will be low geared.
Another option if you saty with the VVT gearbox is to use an auto VVT transfer box as they are lower geared.

Too many options!!

you may be able to get the bell housing cut off and replaced with vvt bell housing will need a alloy welder.
Rob storr was doing this to fit a vit eng into an sj. it would need presion.

I wouldn't have thought the bell housing for a VVT engine would be a different fitting from a M13 engine. In other words the VVT engine is essentially a modified M13.

The gear box bolt's straight up to the motor. A few holes have to be drilled to get the gear box to line up with the original chassis mount's- no big deal. The other thing that has to be done is a shifter mechanism bracket has to be made- no big deal either, its all been done before

I do want to put a rock-lobster t-case in, that's the reason why i am changing box's while i have the chance to....plus this box is meant to be a tad stronger.

Where' can you get 3.9 diff's from? I know a sami rear diff center will fit, but can't not find 3.9's for the front cus it's a high pinon mount center....

From what i have figured.... i will be about 10% under geared....dose this sound right?

3.9 diffs are the standard diff for a non VVT manual car so shouldn't be difficult to find. In addition your 4.3 diffs should be very saleable to non VVT cars with bigger tyres!
The overall gearing is a bit subjective as it rather depends on what you want to do with the car when its finished.
Certainly, for my mind anyway, I prefer slightly lower gearing than higher particularly if you drive a lot of tracks. Its much easier than continually changing between high and low. On the road thay are not the fastest car anyway so as long as at say 100kph its not revving really hard (which mine is - 4600rpm !) 4000 would be nice - its ok.

Are you sure non-vvt are 3.9? I thought they were 4.11?....

Hi Monkey

I'm quite sure - I don't think there is a 4.11 diff. All the autos are 4.09.

www.bigjimny.com/images/documents/transferboxratios.pdf

You guy's must have different diff ratio's to us. We only got 4.09 (not 4.1! 4.1 have one more tooth than 4.09) and our auto's have the same diff ratio's as our manual's....

All VVT jimny's have 4.3 diff ratio's...

Any way i got the car back today with a recon'd non-vvt gear box. The gearing is all out of whack but i have sierra t-case to go in next year.