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Techline - December 2013

Posted in How To: Tech Qa on November 1, 2013
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Rocks vs. Tons
My current dedicated trail rig has a ’41 Dodge body mounted to a ’72 Snow Commander chassis. I’m running a Dana 60 up front with a Trac-Lok and a welded 14-bolt rear. Both axles have 4.56 gears and cut 44-inch Super Swampers. The engine is a fairly stout 400ci Chevy V-8 with roughly 500hp (dyno-proven). The transmission is a Turbo 350 that’s worked and connected to a NP205 transfer case. I’m running 1350 U-joints at both ends as well.

I used to be a big mud guy, but here lately, not so much. I now find myself doing more East Coast wheeling in the rocks, hills, and trails. Mostly places like Rausch Creek and with the Big Dogs at a new park in West Virginia. The problem I have is that my center of gravity is way too high for this kind of wheeling. This led me to pick up an original ’41 Dodge WC-12 frame. My current plan is to link the rear with air shocks and run Deaver leaf springs up front with the 1-ton axles. I would like to use a LQ4 6.0L V-8 for the engine, along with my Turbo 350 transmission and a NP205 transfer case.

Recently, a good friend of mine informed me that he purchased a set of 2½-ton Rockwell axles for me for $600. I’m still not sure I need the Rockwells. The main drawbacks I see are the height and weight of the Rockwell axles. Some people say that I am reaching the limits of my 1-ton axles and that I should invest in chromoly ’shafts and CTM U-joints. Those parts are expensive! I feel that the Rockwells would give me more gear, and if I mohawk the set, then I would have more ground clearance. From what I hear, the 2½-ton Rockwell is about the strongest axle I can run. So what do you think? Do I stick with the 1-tons or go for the Rockwell conversion?
Ken Basile, Jr.
Via email

As a guy that is currently working on a Rockwell-equipped rig (the Rescued Wrangler), I can tell you that the axles have both major benefits and drawbacks. Let’s start by looking at what you have. Judging from the photo you submitted, your rig appears to be fitted with a low-pinion Dana 60 front axle. These are great axles, but do have limitations. If you are still running the stock U-joints and axleshafts and have not managed to break one, then I would say the axle is working fine for your needs.

You mention that the 60 has a Trac-Lok differential. Since the Trac-Lok is a limited-slip differential, it allows more speed differentiation between the tires. This means it isn’t as aggressive or effective as a full-time locker, but it is easier on parts. The biggest downside to the Trac-Lok for your proposed wheeling destinations is that it won’t be as effective and predictable as a full-time locker. For serious wheeling, I suggest upgrading to a selectable or automatic locker.

The fact that your Dana 60 front axle is of the low-pinion group also means that it is weaker than a high-pinion front Dana 60. This is due to the fact that when a low-pinion axle is run in the front of a truck, it applies drive pressure to the weaker coast-side of the gear. A high-pinion Dana 60 front axle is equipped with a reverse-rotation gearset which churns on the stronger drive-side of the gear. Don’t get me wrong. I have seen low-pinion Dana 60 front axles last years under well-used trucks with 44-inch tires, but a high-pinion 60 would be better.

As for the 14-bolt rear, it is one of the toughest and most reliable 1-ton differentials you can have. Sure, chromoly axleshafts would be a great upgrade, but depending on where you are located, factory-replacement ’shafts can usually be had for cheap from your local junkyard. A 44-inch tire isn’t something that I would worry about too much on the 14-bolt, as the extra pinion support and massive 10½-inch ring gear make for an incredibly strong rear axle. With all that being said, the Rockwell option is worth entertaining.

Yes, the Rockwell axles are heavy—very heavy, actually. The massive third member can also make the axle difficult to package under a rig and the gear-reduction internals will be just as power-robbing as your automatic transmission. The good news is that you would be less likely to break a stock Rockwell ’shaft with a 44-inch tire versus a factory 1-ton ’shaft. Stock for stock, the Rockwell is stronger.

As a matter of fact, one of the reasons that I chose to go with 44-inch tires on my Rockwell Wrangler, and previous Rockwell-equipped rigs, is that you can drive like a crazed teenager jacked on soda and Moon Pies. In other words, you can give the rig hell off-road and the axles will usually be none the wiser. This doesn’t mean that you won’t see your weak points appear upstream, but it does make the Rockwell axles very attractive. Going with Rockwells will also require custom wheels, brakes, and most likely, a new suspension setup.

Ultimately, you are in a good position since you own both axles. If your goal is to lower your rig for more technical wheeling, the 1-ton axle set will allow you to accomplish that more easily. The 1-ton axles will also allow your rig to be a touch lighter and nimble in the rocks. If you simply don’t want to drop the coin on the high-zoot ’shafts and 1-ton gear, then yes, the stock Rockwell axles are hard to beat for the price. For your specific trail rig, I would lean more towards keeping the 1-ton axles. Heck, for the money you make selling your Rockwell axles, you could probably get all the axle upgrades you need to make your 1-ton set even better.

SM420 Swap
After installing 31s on my Wrangler, my Jeep’s AX-5 transmission promptly began destroying the synchros. I know from your column that the SM420 transmission is an excellent upgrade. I plan to ultimately run 33s. I have the tranny, Advance Adapters adapter, and bellhousing from a 2.8L GM. My problem is that the casting number on the bellhousing I have is not the same as the one recommended by Novak Conversions. Can you shed some light on the subject for me? I have the clutch, pressure plate, but could also use some guidance as to slave cylinder and throwout bearing.
Noel Enright
Via email

Novak ( lists the GM casting number as 15679692. So long as the bellhousing you have was pulled from an ’85-’89 S-10 fitted with the 2.8L V-6 engine, you should be fine. If your bellhousing is not from the previous mentioned years and engine specs, you may need to look for another one to avoid any complications with the conversion. As for the slave cylinder and throwout bearing, my research indicates that S-10 components from the same late ’80s 2.8L manual transmission trucks should work, but will require a new line to union the Wrangler and S-10 hydraulics. The bellhousing may require a few modifications (slight grinding for clearance) to accommodate the new clutch components as well.

Where To Write
Address your correspondence to: Four Wheeler, 831 S. Douglas St., El Segundo, CA 90245 or send an email to All letters become the property of Four Wheeler, and we reserve the right to edit them for length, accuracy, and clarity. The editorial department can also be reached through the website at Due to the volume of mail, electronic and otherwise, we cannot respond to every reader, but we do read everything.

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