Re-gearimg for 31s and AX15

MattD25

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Raleigh, NC
I apologize, since I’m sure this question has been asked thousands of times, but I get mixed answers and I’m gathering as many resources as I can. Just bought a 98 Sahara with the 4.0 and AX15 5spd manual. Dana 35 rear end just blew on it. Since it needs a rebuild anyways, I’m definitely considering re gearing it. My Jeep expert says for the 31s that are on it, and the daily driving I do with it, I should get 4.10 gears. However I’m getting mixed answers from others. I’ve even used Spicer’s engine RPM calculator for different gearings.

I will be daily commuting about 15 minutes one-way on the interstate, and I want the capability to do some light off-roading (beach sand, gravel/dirt trails at Uwharrie etc). Have two kids under 2, wife and dogs and we all wanna enjoy cruising in it! Without sacrificing too much fuel efficiency, but gaining a little torque on the highways, what do you guys think I should run? Thanks in advance!
 
what's your current ratio? I had a 99 set up the same way with 3.73 gears and I don't think going to 4.10 would have been worth the expense. If you have 3.07's though, then yeah, I think 4.10 would be a good choice.

I believe a lot of 4cyl TJ's came with 4.10, so you could probably save some money picking up a used front axle instead of paying for a regear there, and regearing the rear to match (or pick up a Dana 44 and gear that to 4.10 instead...
 
what's your current ratio? I had a 99 set up the same way with 3.73 gears and I don't think going to 4.10 would have been worth the expense. If you have 3.07's though, then yeah, I think 4.10 would be a good choice.

I believe a lot of 4cyl TJ's came with 4.10, so you could probably save some money picking up a used front axle instead of paying for a regear there, and regearing the rear to match (or pick up a Dana 44 and gear that to 4.10 instead...
Currently uses 3.07
 
I apologize, since I’m sure this question has been asked thousands of times, but I get mixed answers and I’m gathering as many resources as I can. Just bought a 98 Sahara with the 4.0 and AX15 5spd manual. Dana 35 rear end just blew on it. Since it needs a rebuild anyways, I’m definitely considering re gearing it. My Jeep expert says for the 31s that are on it, and the daily driving I do with it, I should get 4.10 gears. However I’m getting mixed answers from others. I’ve even used Spicer’s engine RPM calculator for different gearings.

I will be daily commuting about 15 minutes one-way on the interstate, and I want the capability to do some light off-roading (beach sand, gravel/dirt trails at Uwharrie etc). Have two kids under 2, wife and dogs and we all wanna enjoy cruising in it! Without sacrificing too much fuel efficiency, but gaining a little torque on the highways, what do you guys think I should run? Thanks in advance!
I have a very similar setup as you do: '98 4.0L with the AX-15. I wheeled for a while on 31s with 3.73 gears and it was a good combo. 4.10 gears would've been slightly better. Either way, if I were you, I'd be looking for the take-off axles with stock gears at the local pick-a-part. Both gear ratios were an option, as mentioned above. Good luck to ya.
 
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I have a very similar setup as you do: '98 4.0L with the AX-15. I wheeled for a while on 31s with 3.73 gears and it was a good combo. 4.10 gears would've been slightly better. Either way, if I were you, I'd be looking for the take-off axles with stock gears at the local pick-a-part. Both gear ratios were an option, as mentioned above. Good luck to ya.
I have 3.73s with an AX-15 and 31s. It works pretty well, I even tow a small trailer here in hilly New England without much issue.
 
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I ran 4.10 and 31's for a while on the 4.0 AX15. It was a great upgrade coming from 3.55 but honestly I wanted 4.56 after a while. The desire for 4.56/31 is not really any different from those who love 4.88/33 and 5.13/35.
 
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I ran 4.10 and 31's for a while on the 4.0 AX15. It was a great upgrade coming from 3.55 but honestly I wanted 4.56 after a while. The desire for 4.56/31 is not really any different from those who love 4.88/33 and 5.13/35.
I didn't think 4.0/AX-15 came with 3.55 gears?
 
I have a very similar setup as you do: '98 4.0L with the AX-15. I wheeled for a while on 31s with 3.73 gears and it was a good combo. 4.10 gears would've been slightly better. Either way, if I were you, I'd be looking for the take-off axles with stock gears at the local pick-a-part. Both gear ratios were an option, as mentioned above. Good luck to ya.
I second this. My Sahara had 31s and 3.73s and while it was good enough, 4.10s would have been slightly better, but it wasn’t worth the cost of a regear to go up that step. There isn’t near as much rolling resistance with a 31x10.5 as there is a 33x12.5, so being under geared a step is much more forgiving.

But if you can find both or at least a front axle with 4.10s, I say do it.