Changing Axle Gears in my 2008 Jeep Wrangler JK Rubicon

2008 Jeep Wrangler Rubicon

RPMs at 70 mph with 4.10 gears with 35 inch tires.

RPMs going 70 mph in 4th gear with the stock 4.10 axle gears and 35x12.5r18 BFGoodrich KO2 tires.


RPMs at 70 mph with 5.13 gears with 35 inch tires.

RPMs going 70 mph in 4th gear with 5.13 axle gears and 35x12.5r18 BFGoodrich KO2 tires.


changing gear oil

After 1,000 miles of driving with the 5.13 gears I drained the rear differential case. This was the horrible looking oil that came out. Got me a little nervous that something was wrong. I then drained and replaced the front differential case and the oil looked the same color as well. A couple thousand more miles and I checked the rear oil and it is the pretty golden yellow color as it was when I replaced it. My guess is the shop used some funky conditioner or something that made the opaque silver color.


I will always remember my last trip in my old heavily used 1991 Montero. That trip was to Scout Camp with KB on the East Fork of the Bear River in the Uinta mountains, the last week of July 2018. What a fun trip and great farewell to an old friend that served me well even though she was run down the day I got her over twelve years ago. The Montero ended up being the best $300 dollars I ever spent.

With the passing of my Montero I was in the hunt for a good 4x4 SUV that would take me into places like a side by side ATV. After a long and exhausting search I found that the best option for me was a used four door Jeep Wrangler Rubicon.

As I researched more and more into the Wranglers I knew I wanted one with a little lift, 33" tires or larger, a winch and the locker/sway bar options provided by a Rubicon. I also like the color white and preferred to have a little older vehicle that I wouldn't be afraid of scratching.

After a month or so I found the one I wanted in Logan and a trip or two to the credit union I had my first Jeep — a white with black hard topped 2008 four door Jeep Wrangler Rubicon.

I absolutely love the Jeep however after a couple months of driving it I realized there was one thing that I hadn't researched about with running larger tires — axle gear ratios. The Jeep had 35" BFGoodrich KO2 35x12.5r18 tires which are really only have a 34" diameter when new. My 4 speed auto-transmission with the 3.8 L engine and stock 4.10 axle gears just didn't have enough power to use fourth gear. Unless I was driving downhill I had to turn the overdrive (4th gear) off. 

Weeks of studying gear ratio charts and talking with other Jeep owners I decided I better get the axle gears changed out. Wanting the jeep to last me for a very long time so I felt it best to get the gears changed over as soon as possible. I knew this had to be causing added stress to the transmission and engine by effectively only being able to use three gears of the transmission. I was running some higher than desired RPMs with only being able to use three gears instead of four.

The gear ratio I decided on was 5.13. This would take the gear ratio up three steps from the 4.10 stock gears that were in it. A lot of people tried to get me to go with the 4.88 gears but I really never felt this would offer enough power and I am so glad that I didn't get the 4.88 gears. One of the things I factored in in going with the 5.13 over the 4.88 is that my Jeep has really heavy Rock Slider bumpers and a heavy winch. I also carry a lot of heavy tools and a high lift jack. With the heavier equipment it further helped me decide to go with the lower gears.

I really like the 5.13 gears. I can travel up most interstates in forth gear even on climbs. Some of the steeper grades it does have to downshift to maintain 60+ mph.

If I could do it over again I would really like to try the next step lower 5.38 gears. 5.38 gears are the lowest gears you can fit in the Dana 44 axles that my JK Rubicon has front and back. One of the reasons I probably would prefer the 5.38 gears is when I get new tires. I'm not particularly fond of the KO2 tires I currently have. They are a good tire but I want a more aggressive mud terrain tread on my next set of tires. I'm looking close at the Nitto Trail Grappler Mud Terrain tires and from what I have been reading they are a true 35" tire thus lowering my RPMs from the 34" KO2 tires I am currently running. 

Another thing to keep in mind is that I use a Superchips programmer to get the tires size and axle gears correct. I actually have the tire size set for 33.75" to get the correct MPH using my phone's GPS to verify my speed.

After 500 miles or so of driving it was recommended to me to drain the gear oil and replace it with some new oil. After a bunch of studying on gear oils I chose to use Lucas 85W-140 Heavy Duty Gear Oil. Researching gear oils I found that synthetic gear oil did not transfer heat away from the gears as well as traditional oil so I went with this Lucas 85W-140 Heavy Duty Gear Oil over the synthetic 75w-140 that the owners manual recommends.

6mm Creedmoor Handloads and Ballistics

3 Shot 6mm Creedmoor group, 103 ELD-X

This 100 yard, 103 Gr ELD-X, 6mm Creedmoor group is exactly 1/2". It fits under a penny and almost under a dime. The third shot was the high one. I felt like I was a little high on the target when the trigger broke. Some might want better groups but this is perfectly fine for me.

Below are my personal favorite loads for my Browning X-Bolt rifle(s). To view the loads you will need to read the warning near the bottom of the page, then accept the warning by checking the box inside the warning.

So far the only bullet I have been playing with in my 6mm Creedmoor X-Bolt is the 103 Gr Hornady ELD-X. I've been really liking the ELD-X bullets from Hornady and have been moving more and more of my rifles over to these bullets.

If you are needing printable targets for sighting in your rifle you can get them here.

WARNING: The load information on this page is for my personal use in my personal firearms and is posted for entertainment purposes only. If you chose to reload the 6mm Creedmoor use only data contained in current manufacturer's reloading manuals. Incorrectly reloaded ammunition can cause serious personal injury and damage to the firearm due to excessive pressure. Reload only after proper instruction and in strict compliance with instruction and data contained in current manufacturer's reloading manuals. If you choose to use my load data on theDIYhunter.com you are doing so at your own risk. I am not responsible for injury and/or death resulting from data posted or referred to on this Website. Improper reloading is dangerous. Users assume all risk, responsibility, and liability for any and all injuries (including death), losses or damages to persons or property (including consequential damages), arising from the use of any data posted on this site. If you have read and accept this warning check this box to view my 6mm Creedmoor load data.

X-Bolt Hell's Canyon Speed Rifle — Setup Lightweight and Long Range Ready

Lightweight Hunting Rifle - X-Bolt Hell's Canyon Speed 300 WSM

I often get asked what my favorite scopes are for my rifles. For my long range hunting rifles, my favorite scope has been the Vortex Optics HS-LR 4-16x50 with the generous 24 MOA per rotation elevation turret and a capped windage turret. In my 28 Nosler X-Bolt I can dial up shots waaaaay out there with this combination. So why did I break from Vortex and go with this Leupold scope for my Browning Hell's Canyon Speed X-Bolt?

I wanted to keep this rifle really lightweight. To do so I needed a scope with a short windage cap to make sure that the fat WSM shells cleared the turret on ejection. Why do I need a small windage cap? Because with a scope with large windage caps that is mounted close to the barrel does not provide enough clearance for shells to eject... so you either have to raise the scope up a lot or go with a small windage cap. If I raise the scope up high enough for clearance on ejection I then also have to put something on the stock to raise the comb hieght up for proper head postitioning behind the scope. To keep it lightweight and simple a small windage turret is the best option.

I also wanted to have the ability to dial up most of my shots and have a capped windage turret.  So here is my solution. I have went with a 4.5-14x40 VX-3i with 30mm tube (had to get 30mm tube to get an adjustable objective) and I had the Leupold custom shop place an Impact 32 MOA reticle in it. I also have one of Vortex's small steel bubble levels mounted around the scope tube as well.

I really like the setup for keeping my rifle lightweight. If I had a Vortex, Nikon, Burris and many other brands of scopes I would have to put the scope up on a rail or use really high rings. With a scope up so high I would then have to build comb height adjustment into the buttstock.

What I have now is a lightweight long range hunting rifle that shoots Hornady 200 Gr ELD-X bullets sub 1/2 MOA. I have an awesome tree showing 32 MOA of holdovers in the reticle, I can dial up 14 MOA on the turret (700+ yards) and I have a sticker on the top of the turret marked with actual yardages to dial, currently set for 6,500 ft of elevation. I can always place another sticker on the cap and mark it for a different elevation and bullet combo.

This rifle as shown with a full magazine and a Clincher sling has a total carry weight of 8 lbs 1 oz.

 

 

Additional information