Here is spare rear axle being rebuilt and converted to a full-floater in the comfort of my shop. This is not a step-by-step rebuild guide. You will need the factory service manual for that, especially for the clearances and torque values. Instead, this is a general overview on the subject, including some tips I've learned. The axle section of the factory manual is a muddled mess with many items way out of order. I'd suggest reading through here first.

This axle was supposedly professionally rebuilt several owners ago and has not been installed since. The more I investigate, it looks like it simply had new bearings and seals installed with all shims put in as before. For example, the axleshaft end play was so tight I initially thought it had a Powr-Lok. Should you replace any bearings, you'd need to adjust any settings that were disturbed. The shims are not standard sizes available at most bearing supply houses. Pre-order a shim kit from any vendor of Willys parts to save time.

Ric Meagley's website shows an axleshaft replacement on Mighty Mo, his racing Jeep. I haven't shown much about the disassembly procedures as I started with a bare axle assembly on the workbench.

Only the axleshafts, wheel hubs and a few incidental parts are the same between the Model 41 and 44. However, the procedures to rebuild or upgrade either axle are similar. The pinion gear shaft shim details are slightly different.

My plans are to convert my Model 41 to a full-floater for easier flat-towing with locking hubs. You may wonder why I'm bothering to convert my Model 41 to a full-floater. Warn even sells a full-floater kit for the later versions of the Model 44. The Model 44 is well-known and respected in off-roading circles as a tough, reliable axle. The main reason I'm keeping my Model 41 is simply because that's what I already have. I have seen and heard a lot of comments that the Model 41 is a weak, red-headed stepchild. After some admittedly biased research, I could find no one to tell me exactly why the Model 41 is weaker than the Model 44. It seems to be an old wives' tale. The Axle ID Guide at Offroaders.com perpetuates the myth. (Would anybody like to let them know that uncredited guide originally appeared in FourWheeler Magazine?)

As the world's only Model 41 apologist (look it up), I've received a lot of interesting mail on the subject. In the words of Scott from Michigan, I'll let him explain in his own words how he grenaded Dana 41 and 44 differentials with equal aplomb while somehow the axle shafts held up okay:

"How did I grenade them you ask? Well about 18 years ago my buddy and I had foolish burn-out contests while at the ripe young foolish age of 16. The only way I could burn the tires on the old girl was to pop her into reverse while moving forward (preferably down a hill!), dump the clutch and stand on it! Usually took out ring and pinions!"

(This is just a hunch on my part, but if there are any unsolved mysteries at Scott's old high school, such as who flushed the cherry bomb down the toilet, Scott might be a prime suspect.)

I talked to some shop owners who were axle gurus and solicited comments from the members of the Willystech Mailing List. The weak point on the Model 41 is the axleshafts, generally on the short side. Other than Scott's abuse as detailed above, that is the only failure I've heard about on the Model 41, even on V8 equipped rigs with huge tires. A reasonable guess is the longer axleshaft can twist more, like a torsion bar, so the short side breaks first. But the curious part is the early Model 44 axles used the same exact axleshafts. If you broke the axleshaft in a Model 41, that same exact axleshaft would have broken in the supposedly stronger Model 44. Here is a picture, courtesy of Ric Meagley, of a pair of broken Model 41 axleshafts. Note how they twisted just outboard of the side gears in the differential:

If that weren't enough to convince you, how about duty in Chuck Pedretti's CJ-2A? This isn't some curb-hopping Sunday driver, but a full-blown rock-hopper driven by a man whose sanity may be in question. Recently, Chuck broke the front and rear output shafts in his Dana 18 transfer case before finally finishing off the axle shafts in the Dana 41. Just like in the photo above, the axleshafts twisted immediatedly outboard of the splines although they didn't break. The wheel hubs also were cracked in the keyway area. Remember, the axle shafts and keyed hubs were exact same parts used on the Dana 44 for many years. Chuck graciously provided a picture showing the carnage inside the transfer case:

Later versions of the Model 44 went to a higher spline count at the side gears, which made a dramatic increase in strength. The early 10-spline axles required a deep groove cut into the axle surface, leaving a smaller effective diameter. Instead of cutting, later versions with the higher spline count were formed by rolling. This is a much stronger metalworking process which also has a larger effective diameter at the base of the splines. The latest versions also had one-piece flanged axle shafts, which were much stronger than the keyed hub arrangement.

With a bit of speculation from fellow WillysTech members, I think I learned why the Model 41 was phased out of production. The axlehousing did not have the physical dimensions needed for numerically lower gear ratios. In the postwar period, this faster gearing was needed to utilize the more powerful engines and better roads becoming available. In the redesign, the Model 41 was refined and became the Model 44 due to the new axlehousing. In my humble opinion, there was no significant increase in strength until the higher spline count axleshafts were introduced.

Part of the Model 44 mystique may have come from the extra thickness of the ring gear. A numerically lower gear ratio requires a larger diameter pinion gear, so the mounting surface for the ring gear had to be offset further to compensate. If you compared a Model 41 and 44 ring gear with the same ratio, the one from the latter is much thicker. Of course this looks incredibly stronger, but most of that metal is little more than a spacer for the offset mounting surface. The gear teeth, a major factor in overall strength, are nearly identical on both versions. The Model 41 ring gear is even slightly larger in diameter, a popular measure of relative strength.

In some ways, it might be easier to swap in a Model 44. But while I'm at it, I may as well upgrade from the Flathead 4 motor and T90 transmission. Before I know it, I'd have an ultramodern Jeep instead of a 1948 CJ-2A. My full-floater conversion is merely to allow easier flat-towing behind our camper, so that will be the extent of the upgrade. I even have a spare Model 41, so I have plenty of parts.