Need advice / recommendations on gear ratio and diff locker...

[canyonfireguy]

Hey gearheads,

I need some advice on gearing down and installing a locker, or at least a LSD cassette in my '99 XJ. It has a 3.5" lift and I am running on 31s, but would like to possibly go up to 33s once I cut the fenders and put on Bushwhacker flares. Anyway, it has a manual trans, so the current gear ratio is 3.07:1. I would like to get it back to feeling more like the factory gearing and get some of my low end torque back. I am also thinking that I don't want to mess with air compressors, so a passive LSD, posi, or locker would be best, or maybe electric.

Would be very grateful for any recommendations on the best gear ratio and LSD / locker assy to install. Thanks.

 

[Anak]

Speaking as someone else who is running a manual trans, you are going to want to go deeper than 4.10s. I am running 4.10s and 30" tires. I am happy with that combination, but I don't think I would be happy if I were to go to 33" tires.

As to a locker, I also wanted to avoid dependence on an air compressor. I went with an OX Locker and am quite happy with the result. I have been running it for several years now and it has worked flawlessly for me. I believe the key to success with the OX Locker is the routing of the cable. It needs to be run like an e-brake cable, with the same provisions taken to keep it out of harm's way. Here is my write-up on that front: https://www.naxja.org/forum/showthread.php?t=1143723

 

[canyonfireguy]

Speaking as someone else who is running a manual trans, you are going to want to go deeper than 4.10s. I am running 4.10s and 30" tires. I am happy with that combination, but I don't think I would be happy if I were to go to 33" tires.

As to a locker, I also wanted to avoid dependence on an air compressor. I went with an OX Locker and am quite happy with the result. I have been running it for several years now and it has worked flawlessly for me. I believe the key to success with the OX Locker is the routing of the cable. It needs to be run like an e-brake cable, with the same provisions taken to keep it out of harm's way. Here is my write-up on that front: https://www.naxja.org/forum/showthread.php?t=1143723

Thank you for the great info. Most helpful. I think I'm giving up on the idea of 33s. I think I would need more lift. I went with the 3.5" instead of the 5.5" because I don't want to futz around with brake lines or dropping the t-case, which I ended up having to do anyway. My 31s rub a tiny bit as is.

So with 4.10s and 30s, what are your RPMs like on the highway, and would you say that it's about like the factory gearing or lower?

I have considered the Ox locker. I read an online review from a guy who sounded pretty skilled and he said that he had to take an angle grinder to the case of the locker to get it to clear the diff housing / cover with proper backlash in his Chrysler 8.25 diff. That kind of turned me off. Right now I'm leaning toward a Yukon LSD cassette, or an Eaton E-locker. Just kind of researching it and exploring the options right now.

 

[lawsoncl]

Yeah, I think 3.5" is a little sort for 33s. I ran 4.11 with 32s and an automatic for quite awhile before swapping in the AW4. I'm pretty happy with the 4.11, AW4, 32s, and about 5.5" lift on my MJ.

Here's a rpm/speed calculator for ya.
https://purperformance.com/p-29669-rpm-calculator.html

The ratios on your AX15 are 3.83, 2.33, 1.44, 1.00, 0.79 (1st->5th)
For comparison, the ratios on the AW4 are 2.80, 1.53, 1.00 & 0.75 (1st->4th)
earlier 21-splined AW4s had a .79 4th gear.

 

[boncrshr]

Hey gearheads,

I need some advice on gearing down and installing a locker, or at least a LSD cassette in my '99 XJ. It has a 3.5" lift and I am running on 31s, but would like to possibly go up to 33s once I cut the fenders and put on Bushwhacker flares. Anyway, it has a manual trans, so the current gear ratio is 3.07:1. I would like to get it back to feeling more like the factory gearing and get some of my low end torque back. I am also thinking that I don't want to mess with air compressors, so a passive LSD, posi, or locker would be best, or maybe electric.

Would be very grateful for any recommendations on the best gear ratio and LSD / locker assy to install. Thanks.

I recently lifted my Jeep and am running 33s. I have the AW4 (so not really applicable to you), and I went with 4.56 and I kinda wish I had went with 4.11. At 65mph the rpm is ~2400. I may get 35s next set of tires because I have plenty of clearance. Point being, unless you tow a lot, I would err on the lower RPM side.

As far as lockers, I put approximately 200K with an Aussie locker with no complaints and will do again. In fact, the shop that re-geared my 8.25 said the locker looked fine and were going to re-install with the new gears, but with the new ring gear it wouldn't fit. Come to find out, you have to grind 2 of the teeth down to fit a lunchbox locker in an 8.25 with 4.56 gears. Yukon Gear has a youtube tutorial video.

 

[xcm]

4.56 and an ARB. Installing an arb compressor is easy, and it’s cool to have on board air.
I wouldn’t want to run anything automatic where it will see snow/ice.

 

[lawsoncl]

I wouldn’t want to run anything automatic where it will see snow/ice.

I agree. Having had an ez-locker in a wrangler, you had to be real careful hitting the gas on a curve to avoid it locking up and kicking the back end out. Clutch-pack limited slip, torsen-gleason (torque sensing type) , or selectable is much better on slick roads.

 

[SlowXj]

Don't let lift height control your tire selection... 35s and 3.5 inches of lift work well imo.

Sent from my SM-A426U using Tapatalk