Rear axleshafts in my Jeep last me about two years. Not that I break them-I just replace them to help prevent breakage. I run this homemade high-pinion Dana 60 with some quality aftermarket full-floating axles. I used to run locking hubs on them, but got tired of breaking the hubs, so I went to drive flanges. Maybe I should have kept the hubs as a "fuse" in the system, but I hate breaking things and having to do trail repairs.
Whenever I install a new axle, I paint a straight white line the length of the shaft. This way, I can periodically pull a shaft and check the straightness of the line. It works as a great indicator of any twisting action. I also look closely at the splines for any deformity or twisting.
Any twisting at all calls for a replacement. I'm not really sure just how far an axle can twist before it will break, but I have never broken one. I'm sure a lot of that depends on the alloy and the heat treatment. My wife and I spend a lot of trail time off by ourselves, and replacing something before it gets to the point of potential breakage is kind of important to us.
Yes, to go through axleshafts every two years seems a bit excessive, but there are at least four reasons for doing so. This Jeep sees a lot of trail use, it has 37-inch tires on it, and the axleshafts are only 1.31-inch-diameter, 30-spline units. Combine that with some low gearing and a heavy foot connected to a 450 lb-ft motor, and you can better understand. Several times I have looked into building a new rearend with 35-spline axles, but I'm not sure I want to spend the time or money to do so.
I decided to look into what's called cryogenic processing, where the object is brought down to sub-sub-zero temperatures and held for a preset time. A lot of the local sawmills and wood product mills use the process to extend the life of saw, cutter, and chipper blades. With cryogenic processing, the treated materials gain toughness, stability, and wear resistance. They are also less brittle.
But I still didn't know enough about the process to know if it would actually increase the strength of my axleshafts. The equipment manager of the local power company which uses the cryogenic process on its chain-saw and chipper blades, directed me to Unlimited Possibilities (406/261-3330, unlimitedpossibilitys@yahoo.com), where I talked to owner Les Walter. He explained the process and assured me that there definitely was an improvement in axle strength by subjecting them to the process. In fact, drag racing was one of the things that got him into the business.
I'm still not exactly sure how the process works, but here is how Les explained it: The part goes into a specially constructed computer-controlled tank for about 72 hours, where the temperature is reduced to minus-300 degrees Fahrenheit in very accurate increments. Different time and temperature profiles are used, depending on the material. Now the magic happens in the form of changes in the material's microstructure.
According to Les: "Almost all of the austenite (a soft form of iron) retained in the steel after heat treating is transformed into a harder form, martensite, by deep cryogenic processing. A fraction of the austenite forms into martensite with each decrease in temperature. The cryogenic treatment allows for the continuation of retained austenite to completely transform into martensite. In addition, fine carbide particles, called binders, are produced to complement the larger carbide particles present before cryogenic treatment. Fine carbides enhance the strength and toughness of the martensitic matrix. Cryogenic processing is proven to increase the strength and durability of the material being treated, relieve the internal stresses in the treated part, create a more uniform material, and micro-smooth the surface."
Did you get all that?
Les says he has cryogenically treated everything from axles to yokes with excellent results. These include brake drums and rotors, camshafts, dental instruments, and gears. Weird things include light bulbs, spark plugs, and even CDs and DVDs, all of which have shown a greatly increased life cycle.
I shipped them some new axleshafts, paid them $50, and a week later had them back. Do my axles look or feel any different? Nope, not at all, as there were no color or dimensional changes. I can only go on Les's word that they are different-that is, a lot stronger. It has now been two years since I installed them, and I just pulled out one for a look: No twisting of the splines. I can't say I've used the Jeep any harder or easier in this time period, but I will say the next time I replace an axleshaft, be it front or rear, I am going to ship it off and have it cryogenically treated.
