Gearing Discrepancy

[2006TJ1]

I am a senior in high school, and for my senior year, we have to do a senior capstone project. We have a couple options: research college, complete some applications, etc, and I am going to college, but I wanted to go the hands-on route. After talking with a local dealership/service dept, the GM said he will pair me with his best tech & we are going to regear my Jeep. I went in today to smooth out the details, and he asked me what gearing I thought we should do. Of course, I said 5.13 because I have 33s and the 4spd transmission. He (the GM) wasn't sure what was ideal, so he called his buddy that owns a Custom Jeep/4x4 shop. He told him my setup, and the guy says "I would say 4.10"..... I was pretty shocked. I asked if that is still what he would recommend considering I have the huge OD in the 4spd, and he said "Maybe 4.56 if you are thinking about going to a bigger tire."

So my question is, why would ANYone recommend 4.10 for 33s/4spd? I will be upfront with the tech when I actually talk to him about it and say that I have been strongly suggested to go much lower to get his opinion. But why on earth would the owner of a 4x4 shop think 4.10 is suitable for the 4spd? I can't say I've driven Jeeps with an array of different gears to experience what different gearings feel like, but 4.10 would be a huge mistake, right?

Also, he recommended Yukon. Should I suggest Revolution?

 

[glwood]

You should suggest, even demand, if possible, Revolution.

This seems to happen over and over again with 4x4 'experts' in gearing shops. The only thing I can think of is they are used to regearing V8 monstrosities, where the gearing is not so critical. To regear your TJ with 4.10 or even 4.56 with the 42RLE & 33" tires would be a complete waste of time and money. You want 4.88 at a minimum, and 5.13 ideally. You hit it right on the nose, and need to either convince this shop, or look for another installer.

 

[Jerry Bransford]

The GM's buddy in the Custom Jeep/4x4 shop is clueless when it comes to regearing Jeeps that have your 4-speed automatic transmission. That particular transmission (42RLE) has such a steep (.69) Overdrive ratio that the axles need to be geared to lower than commonly thought of ratios to allow the engine to run at an efficient rpm.

Your 5.13 opinion was exactly correct for running 33's with the 4.0L and your 4-speed automatic transmission. That ratio will produce ideal highway rpms while also working great for offroad use.

 

[Rob5589]

Many people think 4.10 is low, 4.56 being crazy low. They are just uniformed and/or ignorant when it comes to gearing. Should have mentioned stock Rubicon gearing is 4.10 with 31.5" tires, and it isn't low enough with the 4 spd auto. Stick to your guns, you are right on with the 5.13's.

 

[2006TJ1]

Okay, thanks y'all. @Jerry Bransford my 5.13 "opinion" really was yours, I can't take any credit. Everything I've learned has been from y'all on here.

When he said 4.10 I thought "Maybe he meant 5.10 and just didn't realize 5.13 is the closest" but sure enough, he also suggested 4.56, confirming he was definitely thinking in the 4s.

@glwood I will absolutely request/demand Revolution as I will be supplying the parts. I'm not getting any warranty since I will be doing much of it myself, so I will get the parts on my own anyway. Unless of course, they could get them at a lower price, but I don't see how.

@Rob5589 Good point. I will definitely bring that up. Any person who tries to disagree with that obviously has no knowledge or even logical thought.

 

[jjvw]

Show them grimmjeeper.com.

Ask them which of these stock gearing and transmission combinations is preferable.

42rle / 29.5" /3.73 = 2052rpm @ 70mph
NV3550/29.5"/3.73 = 2320rpm @ 70mph (nearly 300rpm higher than the 42rle)
AX-15 / 29.5" /3.73 = 2349rpm @ 70mph (nearly 300rpm higher than the 42rle)
NSG370/29.5"/3.73 = 2498rpm @ 70mph (over 400rpm higher than the 42rle)
32rh / 29.5" / 3.73 = 2974rpm @ 70mph (nearly 900rpms higher than the 42rle)

 

[Chris]

4.10 gears with 33" tires and a 42RLE transmission? :risas3:

That's the worst advice ever.

 

[2006TJ1]

Show them grimmjeeper.com.

Ask them which of these stock gearing and transmission combinations is preferable.

42rle / 29.5" /3.73 = 2052rpm @ 70mph
NV3550/29.5"/3.73 = 2320rpm @ 70mph (nearly 300rpm higher than the 42rle)
AX-15 / 29.5" /3.73 = 2349rpm @ 70mph (nearly 300rpm higher than the 42rle)
NSG370/29.5"/3.73 = 2498rpm @ 70mph (over 400rpm higher than the 42rle)
32rh / 29.5" / 3.73 = 2974rpm @ 70mph (nearly 900rpms higher than the 42rle)

I'll show the GM and see what he says. Honestly, I think gear talk was a little out of his comfort zone because as soon as I started talking numbers, he called his friend. I wish I could show that guy, maybe I can call him and ask for a way to show him that chart... If the GM doesn't tell me no then I'll probably just end up ordering what I want because like I said, he's not even doing the install with me.

 

[Jerry Bransford]

I'll show the GM and see what he says. Honestly, I think gear talk was a little out of his comfort zone because as soon as I started talking numbers, he called his friend. I wish I could show that guy, maybe I can call him and ask for a way to show him that chart... If the GM doesn't tell me no then I'll probably just end up ordering what I want because like I said, he's not even doing the install with me.

Just tell him you did your research with a half-dozen experts in ratios for the Wrangler with your 42RLE transmission and they all agreed 5.13 is the correct ratio to go with. Perhaps also let him know that his buddy probably didn't get that your transmission is the 42RLE which requires a much lower than usual axle ratio for the Jeep to run well.

 

[Vcook]

Just tell him you did your research with a half-dozen experts in ratios for the Wrangler with your 42RLE transmission and they all agreed 5.13 is the correct ratio to go with. Perhaps also let him know that his buddy probably didn't get that your transmission is the 42RLE which requires a much lower than usual axle ratio for the Jeep to run well.

This is the right answer. No need to be argumentative, just confident that after doing the research this is the direction you want to go.

 

[Andy5150]

A lot of these shops work on big v-8 , or diesel pickups with light years more toque than the 4.0 Jeep . They should know they're dealing with a 242 cu.in. motor that needs to wound up tight to do anything.

 

[JMT]

Yeah, like Jerry said, no need to argue, you’ve done your research. The guy who called his Jeep buddy was just looking out for you. But in the end it’s your Jeep. Great opportunity to get your Jeep regeared. Great learning experience! Great price!

 

[AndyG]

I'm regearing my 03 Rubicon with 5 speed nv 3550 and 33" ko2s to 4:56 as I text this .

If it were an automatic , I'd go even lower .

Basically, everything I've read on the forum is based on real experience..not just theory.