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Re-gearimg for 31s and AX15

MattD25

New Member
Joined
May 10, 2022
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7
Location
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!
 

freedom_in_4low

Sacred Order of the Coil Spring
Supporting Member
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Sep 26, 2019
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4,870
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Edmond, OK
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...
 
OP
MattD25

MattD25

New Member
Joined
May 10, 2022
Messages
7
Location
Raleigh, NC
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
 

SvtLdr

Search Engine Certified Mechanic
Supporting Member
Ride of the Month Winner
Joined
Nov 26, 2019
Messages
1,776
Location
NE Indiana
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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jeepguy03

TJ Addict
Supporting Member
Joined
Jul 23, 2020
Messages
1,275
Location
Connecticut
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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machoheadgames

LED turn signal club
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Jan 21, 2021
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956
Location
Dallas, TX
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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jeepguy03

TJ Addict
Supporting Member
Joined
Jul 23, 2020
Messages
1,275
Location
Connecticut
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?
 

Jamison C

Can't keep it in my wallet
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Sep 1, 2018
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2,433
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Sedona, AZ
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.