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Diff ratio from 2005 into 1999 Jimny prep for 215/75 15
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Author:  jaszuki [ Sun Oct 11, 2015 7:12 pm ]
Post subject:  Diff ratio from 2005 into 1999 Jimny prep for 215/75 15
My car is a 99 G13BB manual, lifted 60mm. I've taken a front axle from a 2005 M13A manual. From what I've been told and read (although with a few discrepancies) my G13BB ratio is a 3.9. The 2005 M13A is 4.3. Are these figures correct? I don't want to have to open them up to count the gears unless I have to... Is there a number stamped on the housing that can help identify them?

Next question, I'm planning on running 215/75. Will the 4.3's be sufficient to drive these and how far could you go, tyre size? Are there going to be issues with indicated speeds on my tacho and what can be done to resolve them. From what i've read it should be good?

Please feel free to suggest appropriate read ups. My search terms are pulling too many numbers.

Jase
Author:  watermouse [ Sun Oct 11, 2015 8:04 pm ]
Post subject:  Re: Diff ratio from 2005 into 1999 Jimny prep for 215/75 15
The only way to know for sure is to count. You can also do this without disassembly by counting revolutions of the drive shaft to one wheel rotation. My 99 jimny was 4.09 as I believe all G13 Jimnys sold in Australia were.

I had 215/75 on mine and didn't ever feel the need for a ratio change. You might if you want to run any bigger tyre though.

You should try and match tyre diameter % change over stock with ratio % change. If it is ~5% or less, IMO, it is not worth the hassle.
Author:  fordem [ Tue Oct 13, 2015 12:05 am ]
Post subject:  Re: Diff ratio from 2005 into 1999 Jimny prep for 215/75 15
watermouse wrote:
You can also do this without disassembly by counting revolutions of the drive shaft to one wheel rotation.


It's easier to do it to TWO wheel rotations.

Chock the front wheels, jack one rear tire off the ground, and count the drive shaft revolutions for two full rotations of the wheel you have off the ground - this is needed because of the differential action that occurs when one wheel is stationary and the other one rotating. You could do it for one rotation, but you'd have to jack both wheels up and make sure they both rotated the same amount to prevent differential action from affecting the count.
Author:  monley [ Tue Oct 13, 2015 4:20 am ]
Post subject:  Re: Diff ratio from 2005 into 1999 Jimny prep for 215/75 15
As watermouse said g13(manual) jimnys only come with 4.09 in Australia. As for the donor, 2005 was the cross over year from m13a to m13a VVT. If its just a m13a it will still be 4.09 but if its the VVT model it will be 4.3. Thats all for manuals though.
Author:  watermouse [ Tue Oct 13, 2015 8:31 am ]
Post subject:  Re: Diff ratio from 2005 into 1999 Jimny prep for 215/75 15
fordem wrote:
watermouse wrote:
You can also do this without disassembly by counting revolutions of the drive shaft to one wheel rotation.


It's easier to do it to TWO wheel rotations.



that is good advice.
Author:  jaszuki [ Tue Oct 13, 2015 5:10 pm ]
Post subject:  Re: Diff ratio from 2005 into 1999 Jimny prep for 215/75 15
Thanks for all the advice.

The wreckers I got the front diff from did say it was a 4.3 so i'm going to assume that it's from a VVT model until I call them up to confirm tomorrow.
If it's worth a mention, if driving at 100km/h my RPM is sitting one notch below 4000RPM. Does that indicate anything?

I found this reference (http://www.bigjimny.com/images/document ... ratios.pdf) for driveline ratios. Would you say that this is correct?

So the current plan atm is I'm going to get the rear diff from the same vehicle I got the front off. Main reason being is that it's newer and also being a 4.3 it will be useful for the larger tyres i'm going put on the car. As watermouse mentioned it's not necessary for a 4.3 diff to run 215/75 tyres, but what about 225's? If I run 215's with the 4.3 diff, what should I expect with regards to driving quality, torque and acceleration etc. I'm really quite new to playing around with diffs, ratio's and tyre sizes. I know that having a 4.3 will allow the car to turn the larger diameter tyres but will suffer at top end speed having to run at a higher RPM, so fuel efficiency will suffer accordingly <---- is that statement correct?

Does someone have some reference with the maths involved so I could work this out.
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