To change diff ratios or not?

H

Hawkeyes

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Jun 27, 2023
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South Africa
Jip, this would have been discussed already somewhere.....

I have a stock standard 2005 4L Sahara in pristine condition, still with 225 75R15 tyers. (about 27") I am seriously considering going to 31" tyers for various reasons.... Mainly looks. I'm not concerned about spedo correction.... My gas mileage is exceptionally good, guess it's the way I drive.

Do I need to change diff ratios, if so to what?.

PS-I live in South Africa.... And my TJ is right hand drive.

Thanks in advance

Paul (South Africa)
 
You don't have to do anything if you don't want to.

But, if you travel over any mountains/hills or like acceleration, you would benefit from the re-gear.

You would need to figure out what you have before we could suggest what to change to.

What is your rear axle ratio and do you have the manual or auto transmission.
 
It's a manual 4L, stock standard, no changes since new.... I generally don't fiddle so no idea what the current ratios are other than it's standard.....
 
Look at the steel tag bolted onto your differential cover at its 9 o'clock position. Embossed into it will be your current axle ratio.

This one in the photo below is indicating the axle has a 3.73 ratio. Since you're in S. Africa you'd have an export version of the Wrangler which means you likely have a Dana 44 axle in the rear which only comes with a 3.73 ratio. I wouldn't bother regearing for 31's with 3.73.

Axle Ratio.jpg
 
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Hawkeyes said:
OK, it is a 3.73, not going to change diff ratios to start with, and will check it out over the next few miles.... Thanks for the info.... The general consensus is stay standard upto 31". Seems like it becomes an issue once you go bigger.
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I live in an area with a lot of steep long hills. the 3.73 on 31's was great! I would leave it as is. I'm on 35's now and geared to 5.13. The 31's and 3.73 were much more enjoyable to drive as a daily driver. For rocks, my set up now is way better. It all depends what the use of your Jeep is
 
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inkedrose said:
I live in an area with a lot of steep long hills. the 3.73 on 31's was great! I would leave it as is. I'm on 35's now and geared to 5.13. The 31's and 3.73 were much more enjoyable to drive as a daily driver. For rocks, my set up now is way better. It all depends what the use of your Jeep is
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Depends on the transmission.

31s and 3.73 are good for the 3spd auto, not anything else.
 
Hawkeyes said:
OK, it is a 3.73, not going to change diff ratios to start with, and will check it out over the next few miles.... Thanks for the info.... The general consensus is stay standard upto 31". Seems like it becomes an issue once you go bigger.
Click to expand...

Correcting your speedometer is very easy. You just change out your speedometer drive gear.

IMG_7797.png
 
Jerry Bransford said:
Look at the steel tag bolted onto your differential cover at its 9 o'clock position. Embossed into it will be your current axle ratio.

This one in the photo below is indicating the axle has a 3.73 ratio. Since you're in S. Africa you'd have an export version of the Wrangler which means you likely have a Dana 44 axle in the rear which only comes with a 3.73 ratio. I wouldn't bother regearing for 31's with 3.73.

View attachment 482956
Click to expand...

Interesting point you make here, @Jerry Bransford . My build sheet indicated a Dana 44 rear and a 3.07 axle ratio (Aussie export TJ), which I just always assumed to be true. Going to crawl under right now and double check!
 
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