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Help required - transfer ratio issues

  • Dom
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31 Jan 2018 21:47 #189024 by Dom
Hi all,
Firstly; apologies if this is in the wrong section or has been covered already (I'm new here...) but I'm after some advice on options to solve my transfer ratio issue.

I have an old 02 plate Jimny special which I use for light off-road but mostly on-road purposes (also have a land rover for heavy towing and off-road use).

My issue is that the poor little Jimny engine screams on the road, and I'm looking at a way of manipulating the drive ratios, preferably in the transfer box.

The transfer box is the manual type with a 'high' ratio of 1.3:1.
I see the later electronic one is 1:1 so can I fit this or is there a better option?

I'd like to retain the 4wd functionality (not fussed about the low range ratio), and an accurate Speedo would be great!

Do any of you have any experience or ideas on how I can achieve this economically?

Many thanks :)

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  • Busta
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31 Jan 2018 23:35 #189025 by Busta
Whilst the engine revs are relatively high at motorway speeds, this is necessary due to the Jimny's low power, brick like shape and high mechanical resistance. Any efforts to make the drive ratio higher will result in very sluggish performance and even worse economy. In later Jimnys the overall drive ratio is lower and yet they achieve better performance and fuel economy. The good news is that the small 16v engines used in the Jimny are very reliable and happy running at high rpm for days on end, so if you can get over the fact the needle is pointing at the 4 then everything is fine.

If you must change it, the simplest way to achieve what you are after is to fit larger tyres. I run 215/75r15 which have a 5% larger circumference than standard and the negative effect on performance and economy is noticeable. The 30% difference changing the transfer case would make would render 5th gear unusable, and make 1st gear like pulling away in 2nd!

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01 Feb 2018 05:02 #189026 by Lambert
My dad is constantly complaining about this very issue and whenever he drives Ermintrude i am constantly telling him to change down a gear or two. The problem lies in expecting a 1.3 petrol engine to have the same rev characteristics as a turbo diesel with twice the displacement. Quite simply the Jimny doesn't have the torque to pull fifth gear from two thousand revs. In order to make progress in a Jimny you have to be prepared to keep your foot in it way past four thousand rpm in each gear. Like Busta says it's not doing any harm, it's just how they are..

It's not a Jimny. It's my Jimny

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Boing said Zebedee (blue)
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01 Feb 2018 06:38 #189027 by yakuza

Busta wrote: If you must change it, the simplest way to achieve what you are after is to fit larger tyres. I run 215/75r15 which have a 5% larger circumference than standard and the negative effect on performance and economy is noticeable. The 30% difference changing the transfer case would make would render 5th gear unusable, and make 1st gear like pulling away in 2nd!


This is the hard facts. Changing to even bigger 235/75/15 tires like i did, helped even more on the revs on the highway.
But uphill the car is sluggish and slow, and offroad there is allmost no low gear anymore.
(changing from m13 to m16 helped of course.)

2005 Jimny M16A VVT, 235 BFG MT, 2" Trailmaster, 17%/87% high/low gears.

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01 Feb 2018 08:23 #189029 by Busta
Lambert, I've had exactly the same thing with my girlfriend going from a 1.3 td to a 1.0 petrol, expecting it to lug up hills at 30mph in 5th, and complaining it was slow. The petrol is actually the quicker car, and far more engaging to drive but TDs corrupt people's expectations.

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  • Dom
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01 Feb 2018 12:57 #189032 by Dom
Replied by Dom on topic Help required - transfer ratio issues
Thank you for your inputs.

I agree that the 30% change would probably be way too much, so changing the transfer box would probably render the vehicle useless.
A tyre size increase would probably be more subtle so I'm going to look into that, but probably stick to the stock width for steel wheels if I can find some at my local breakers.

So the question of 'can I fit a later version 1:1 transfer box is a definite no, but I'm still curious to know if it can be and has been done...

If mechanically speaking it's a straight swap, then I think I'd like to give it a go and then come back and rant about what a bad idea it was.
In order to try out the 1:1 high rang on the road I wouldn't need any of the electrics connected (assuming the box is in the 2 high already), or the front prop.
So, other than it being a generally bad idea, are there any differences between the manual and electronic boxes on the mounts or drive flanges that will be a problem?

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01 Feb 2018 18:08 #189036 by Riccy
I did the reverse swap (in a round about way).

i found it was possible to fit a stick t-box into a push-button jimny, so i would assume its possible the other way from a nuts and bolts point of view.
The connector for the speedo is the same, mount points are the same and the props are the same spacing/bolt pattern from memory (spline count on gearbox to t-box prop is different depending on gearbox, but t-box end is the same). Electronics beyond the speedo are totally different and would be a headache to splice into an earlier model however.

I suppose you could try and fit one in to see what it does in 2wd high, I would expect it to be fairly un-driveable due to over gearing. As the others say, its designed to rev high and works best like this. Even my 1.6 vvt sits at 4000 rpm for motorway speeds (deliberately geared that way for 31" tyres)

J999 MNY, M16 VVT, R7me gbox & Rocklobster,
31x10.5r15 Cooper STT, 2x ARB Lockd' 3.9 diffs & twin compressor,
6.5" total lift, Zookbob HD steering shock, Ignis recaro's
Custom bar & arches, rocksliders & guards,
Snorkel, K&N, 13500lb Winchmax, Buzzweld, etc, etc

Plus ULYSSES (06' trayback project)

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