For most of my upgrades, I’ve waited until I found I needed them before going out and making them. For example, I took the stock Jeep out on trails in the area until I found that I needed to improve the clearance if I wanted to continue on the trails or try more challenging trails, so I installed a lift. I busted the Evap Can, then relocated it. I found I needed a little taller and wider tire and got 35s. Etc. I was really hoping to keep the 4.10s, but…

With the 35s and 4.10s:
1. The first time I drove it I noticed it needed a little more gas to get going. Over time I noticed that it felt more like the gears had a very slight binding/I had to drive up a very small hump when starting - no real binding/bump - just felt that way.

2. On very slight hills and in 2WD or 4High in Drive the transmission can’t hold and it rolls back.

3. In 2WD or 4High and going 20mph or less there’s almost no difference between D, 2nd, and 1st (no difference in engine braking, torque).

4. On the freeway it kicks out of OD going over simple/small overpasses.

5. On the freeway going up a steeper hill it kicks down to 2nd to keep up.

6. Going down some steep dirt hills in 4Low had to use brakes.

7. Acceleration from stop not great.

8. Crawling on rocks in 4Low and 1st not much worse than stock.

9. MPG: 32s (14.6K miles): 16.1, 35s (2.2K miles): 15.1


With the 35s and 5.38s:
1. Starting feels great. No extra gas needed.

2. Transmission holds on small hills.

3. There’s noticeable engine braking and torque in 2nd and a lot in 1st. 4High is nicer on the trail with the engine braking.

4. Doesn't kick out of OD on simple/small overpasses and small hills. Doesn't seem to struggle at all on these types of hills.

5. On larger hills kicks down to 3rd and holds with no struggling going up the hill.

6. On the same hills additional braking is not needed. On most hills no braking is needed at all.

7. Acceleration from a stop is great - no issues.

8. Crawling on rocks in 4Low and 1st better than stock.

9. MPG: Breaking in gears (500 miles): 16.8, My normal driving (8.7K miles): 15.0


The shop I brought it to recommended 5.13s or 5.38s and after discussing my driving habits and needs we decided on 5.38s. They installed the gears with Front and Rear Master Overall kits and (verbally) they will warrantee the gears for as long as I own the Jeep (assuming I follow their break-in instructions). The upgrade wasn’t cheap, but so far it drives as good or better than stock and better than 35s and 4.10s.

I’ll update the thread once I break in the gears and try more stuff.

 

very nice i have 35s and 3.73s id love to get 5.38s

 

Good info. I just ordered 35's for my Unlimited 6-speed. Have 4.10's. Am going to try it and see if I can use the trans (again, 6-speed) to make up the difference. I'm sure my wife will want to kick my a$$ if I need to get gears next month because the Jeep's a total sloth with the new tires/wheels

 

BBirish - I’m sure you would see a big difference with 5.38s!

Schantin - from what I’ve read, you may just have to give up using 6th gear.

 

I updated the first post with some MPG info.

I’m halfway through the break-in period. Still looking good.

 

Ballpark? $500-$600 to purchase (w\install or overhaul kit), $500-$700 to install (that's front and rear)

 

The gears were about $400. My shop said they require a Master Kit front and rear (I wanted that too), for approx another $400, and the labor was around $550, than add oil and tax.

 

At 500 miles it’s time to change that oil and get your Jeep out on the trails! I can’t wait till we hit 500.

We purchased our Jeep for weekend wheeling, so MPG was not a big factor in our purchase. If the 35s with 5.38s are better than the 4.10s and 32s I’ll really be happy. I doubt we’ll continue to get 16.4 MPG when we take the Jeep out wheeling, but like I said if we do then that would be a great bonus for us!

At 60 and 70 MPH in OD the 5.38s run about 100 rpm higher than the 5.13s. I’m don’t know what the MPG difference would be yet, but I do know that the 5.38s are turning about 500 RPM more then the 32s. Again I don’t have the actual numbers yet (since I haven’t broken in my gears), but I’ve read that an “optimal” cruising RPM range is 2,700-3,000 RPM. I do know that when I ran the Jeep with OD off (higher RPM) I got better gas mileage than with it on (lower RPM). What’s the optimal RPM, I don’t know yet.

For running off-road the better the crawl ratio the more power and control you’ll have. My off-road shop asked me a few questions about my driving habits, how fast I drive, daily driver, off-road usage, etc. and based on my answers he said I’ll really be happy with the off-road performance with the 5.38s. I know I’ve gone down more than one hill, with the Rubicon transfer case in 4Low, in 1st, and still needed to use a little braking. I’m really looking forward to tackling the same hills with the 35s and 5.38s and seeing if I can stay off the brakes. I’m also looking forward to the extra torque and horse power at the lower speeds when crawling up over rocks.

I really don’t think there’s a gigantic difference between 5.13s and 5.38s (like there is from the 4.10s), but since my primary use for the Jeep is off-roading I went with the guaranteed extra performance gain from the higher ratio.

 

Plus if you decide to go to 37s, Your good!

 

That's the same thing the guy at my shop said!