AEV TJ unlimited build

[Dr. Bob]

I am interested in the all around expedition set up TJ LWB,37",4.88,high line,etc. When looking for used TJ unlimiteds is the rubicon worth the extra cost or since most systems are being changed will a standard unlimited be a better investment. Thanks.

[Mieser]

I am working through a similar project....

I am planning on running 37s also. I think that a 37" tire is going to push D44 axles to the edge. I think they need to be upgraded to alloy axle shafts and better U-joints. It isn't so much that the D44s won't hold up to 37s 90% of the time, its that when they do break your going to be far from home. I think the stock Rubicon lockers are going to be pressed hard by a 37" tire. All LJ unlimiteds have a stock D44 rear axle with 3.73 gears. You can also buy an empty D44 front housing for around $600. The knee jerk reaction is to just upgrade to a set of Dana 60s or something. While almost bulletproof this adds a LOT of weight to the jeep overall. There has been some decent work with the 609 axles ( 9" centers with 60 outers ). These are a fair bit lighter than the Dana 60 stuff and in some cases even lighter than the stock D44s.

The best option I have found for the rear D44 is the 35 spline ARB locker with the 35 spline alloy rear axles. I think this system is going to push the rear housing and D44 ring and pinion. An ARB housing cover may help with some of the cast housing flex making the gears last a little longer. The stock D44 rear axle housing and tubes is going to be a little on the weak side for a heavy expedition vehicle. I am planning on trussing mine and perhaps re-tubing it with some heavier wall tubing.

The front axle is a little more complicated. The easy answer is to upgrade to alloy shats and u-jionts, run quality ring and pinions, and a strong locker. The weak point for me is the outer stub axle. It is only a 27-spline unit which is the same as the D30 stock axle. There is a 30 spline upgrade for the front axle, but it uses custom machined front Uni-bearings.

In the end I think your better off going with the non-rubicon and building from there since your going to most likely have to change a lot of the Rubicon parts out for stronger ones.

[Dr. Bob]

Then again my 1981 Scrambler, 4.11,32". 2" body lift is very capable. I am more interested in an upgrade than the ultimate jeep. Practical expedition and road, not rockcrawler capable. Thanks.

[Mieser]

I'm not talking rockcrawler.

As per your original post you want to run 37" tires. Running that big of a tire is going to take its toll on components just on the highway, let alone in the back country somewhere. If your honest about building a capable jeep on 37" tires I think your going to have to address the axle strength.

I know people who have run stock driveline components with heavier 35-37" tires on stock D30 front ends and been fine throughout thousands of miles. I have also known people who have broken 35 spline D60s with 33s. Its not a matter of IF it will break its WHEN and WHERE....

I think you would be pushing your luck in the back country building a LJ that will run a 37" tire with stock axles. If you constantly wheel with friends and have a strong mechanical background and Macgyver skills I say go for it. You can elect to carry spares as backup but I think doing too much of that compounds some of the strength problems in the first place...by going overweight. Here is my suggestion list for spare parts and common breaking points over the years with TJs.

-In general the first thing to go is going to be the rear U-joint at the pinion. This joint is the most abused in the car. At a minimum I would suggest upgrading the yoke to the u-bolt style instead of the strap. I would also suggest carrying a spare and tools to fix it. The Rubicons had a slightly larger driveshaft yoke ( 1330 instead of 1310 ) but it was still a strap style yoke.

-The next thing to go is always the front axle u-joints. This is a pain on a TJ because of the uni-bearing full time rotation of the front axle. If you pop a u-joint in the front and keep driving it really nackers everything up in the front end. The best option is to stop right away and hope that you can slip in another u-joint and the ears are not destroyed. If you can't make a new joint work your best bet is to remove both inner axles ( even if the other side isn't broken ) and the front driveshaft. The outer axles are needed to preload the front wheel bearings so keep those in there....even one with ruined ears will work just fine. Now your front end will be disconnected from the jeep and you will be able to drive home in two wheel drive and still have low range if you need it for the gearing.

-Wheel bearings. As you know the TJs use a uni-bearing joint in the front and a semi-floating setup in the rear. I would highly suggest carrying a spare front uni-bearing. If one of these fails your up a creek without a spare. Remember you have to have the outer axle shaft in place to make them work right. Having a wheel bearing go out in the rear is also a sticky situation. A 37" tire is a lot leverage on those bearings. I would carry a spare rear bearing even though the prospect of fixing it isn't the best on the trail. You need a press to be able to change them and may be able to find one locally. I have seen some pretty ingenious trail fixes that did get them changed but it was neither quick nor easy. A better option for the rear may be a spare short side rear axle shaft. This would function on either side in a pinch and a spare wheel bearing would be on the shaft already and in good shape. This would solve two spare parts functions or more. The downside is that a rear axle shaft isn't a small piece of kit to haul around all the time.

Best of luck with your project!

[Dr. Bob]

Thanks again for the very complete info, would looking at 35" be a more reasonable compromise, as reliability is a major issue, not being much of a mechanic. How does the rubicon regular unlimited comparison wash out with the 35" tires. Can 35"s be run with stock Rubicon gearing without destroying performance. Thanks.

[JeepinJon]

Thanks again for the very complete info, would looking at 35" be a more reasonable compromise, as reliability is a major issue, not being much of a mechanic. How does the rubicon regular unlimited comparison wash out with the 35" tires. Can 35"s be run with stock Rubicon gearing without destroying performance. Thanks.

The 35" tires would be much more livable with the stock axles than the 37" tires would be. You my want to regear down the road, but if you can find a Rubicon that has not been beat up on then this would be the way I would go, and then in the future upgrade to a super 44 kit with stronger shafts, lockers, and regear to like a 4.56, or a 4.88.

[Jdemonto]

You will be fine with 35's on D44 Rubicon axles, Upgarde to alloy usa shafts for peace of mind.

Its all about the skinny pedal...My D30 lasted 54K with 37's..I just upgraded to a D44 with a E-locker and alloy shafts

Jason

[Mieser]

I think 35" tires are a bit better choice overall if your not looking to do a lot of major work.

35" tires will fit with the AEV Highline kit with a very simple OME lift. If your looking into running a manual transmission the factory NSG-370-6 transmission isn't that bad an option with 35" tires and the Rubicon 4.10 gears. The stock 6 speed has a pretty deep 1st gear and a short overdrive so the gearing works out ok. Its not the best option...but tolerable if your not into extreme rock crawling.

On the other hand if your looking for an automatic transmission I think your going to need to re-gear. Personally I hate the stock 4 speed automatic. The first three gears are ok, but the overdrive is WAY too tall. The transmission also has a tendency to hunt between gears, shift too soon, and just not work well. Personally I think 5.13s are about the best you can get for 35s with the factory automatic.

Even with 35s I would suggest using the advice in my previous post about spare parts and the ability to change them out with the proper tools. I would suggest learning to change some of these parts in the driveway before you venture too far out in the boonies....

[Jdemonto]

I would tend to disagree....

I have 37's with 4.88's and I can launch from a dead spot like nobody's business!!!

5.13's would give and even faster launch or maybe a bit more power on the lowend...The I-6 already has enough power in the lower power band.

I see the reason why the Jk's are geared with 5.13's and 35's...the tj has nothing to offer after 3000RPM

Jason

[Mieser]

The problem isn't so much with the I6 low end torque and off the line gearing. My recommendation has to do with the large gap between 3rd and 4th gear with the automatic. The 4spd automatic always seems to hunt between overdrive and 3rd gear....while trying to figure out if it wants to lock or unlock the torque converter. I may be a more picky than most people however. The jump between 3rd and 4th is just too large for the high drag profile of the TJ. It seems like tall .69 4th gear is almost useless once you get off the flats. It tends to down shift to 3rd too late and up shift to 4th to early in most every situation. I think the 5.13s let you use 4th gear more. With 4.88s and 37s I would think that the overdrive would be fairly useless? To be honest I liked the old 3spd transmission much much better. It did a great job. I don't see why they got rid of it. The mileage didn't go up with the new 4spd as far as I have experienced. Overall I tend to favor lower gearing than most people with the 4.0. My overall favorite gearing package was 3.73s with stock 30" tires on the older TJs ( pre 2002 ). The RPMs where up above 3K on the interstate but I always got 17-18mpg with that combo no matter how bad I flogged it, top up, top down, loaded for Moab, whatever. The 4.0 can tolerate a lot deeper gearing than people would think.

[Jdemonto]

The problem isn't so much with the I6 low end torque and off the line gearing. My recommendation has to do with the large gap between 3rd and 4th gear with the automatic. The 4spd automatic always seems to hunt between overdrive and 3rd gear....while trying to figure out if it wants to lock or unlock the torque converter. I may be a more picky than most people however. The jump between 3rd and 4th is just too large for the high drag profile of the TJ. It seems like tall .69 4th gear is almost useless once you get off the flats. It tends to down shift to 3rd too late and up shift to 4th to early in most every situation. I think the 5.13s let you use 4th gear more. With 4.88s and 37s I would think that the overdrive would be fairly useless? To be honest I liked the old 3spd transmission much much better. It did a great job. I don't see why they got rid of it. The mileage didn't go up with the new 4spd as far as I have experienced. Overall I tend to favor lower gearing than most people with the 4.0. My overall favorite gearing package was 3.73s with stock 30" tires on the older TJs ( pre 2002 ). The RPMs where up above 3K on the interstate but I always got 17-18mpg with that combo no matter how bad I flogged it, top up, top down, loaded for Moab, whatever. The 4.0 can tolerate a lot deeper gearing than people would think.


Just got back from the TDS in SOCAL and I averaged 65mph and was in 4th gear most of the way there and back. I got 16.8 MPG to and on the way back 13-14mpg (Strong 40mph winds)

Jason

[jeepgreen]

Dr. Bob,

I bought a 2006 Unlimited from AEV. Kent tried to talk me in to the Rubicon version, but I figured I could save money and upgrade piece meal from the base Unlimited. I was partly right and partly wrong.
I have definitely spent more money adding the parts that a Rubicon would have come with stock (rear driveshaft and lockers) and I still don't have a 4:1 transfer case.
I didn't go with the Highline kit (wasn't available when I bought), but went with tube fenders instead (cheaper) and still able to fit 35" under 2.5" OME and 1" body lift. If you're only going 35's, then base Unlimited will work for you. Axles easily able to hold up and can even be upgraded for extra insurance.
If you're going 37's, don't bother with the Rubicon because the Rubicon 44s still won't be up to the task. Buy the Unlimited and put the difference into other axles.
I have the I6 and 6-spd manual with 4.88 gears. Lots of power to pull hills, even in 6th. I could probably even get away with 4.56 with the 35's.