How to adjust half-floating axles?


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Posted by David Sherman [72.47.9.228] on Sunday, November 28, 2010 at 14:54:44 :

Now that it's snowing I'm finally getting around to putting the Sno-Cat back together. It has dodge corporate 1/2-ton rear axles at both ends. I'm told they are 8-3/4 rears that were used, with variations on lot of mopar cars and light trucks. I've only worked on full-floating rears, where you can pull the axle shaft out while the hub is still attached to the housing, and all the axle shaft does is transmit torque, not carry any weight.

These have a separate tapered keyed hub that goes over the tapered end of the axle shaft. Before you put the hub on, you assemble a single timken bearing assembly (cup and cone) and seal over the end of the shaft. The seal retainer bolts to the housing and holds the bearing cup from coming out. This keeps the axle shaft and wheel (or pontoon on the Sno-Cat) from coming out of the housing. What keeps the shaft from going in too far is that it hits on the shaft from the opposite side inside the ring gear. This mans that the preload on the bearings is a function of the overall length of the axle housing, the length of the 2 axle shafts, their seal retainers, and bearings. In other words there are a lot of tolerances that stack up.

When I took mine apart it had one shim on one side. I'm obviously not going to be able to just go out and buy a stack of shims of various thicknesses to get it right. Also, I don't know how to tell when the pre-load is right. Just keep taking out shims until the shafts can slide back and forth and then add one more in so it's tight? Or should it slide back and forth a little? Is there supposed to be a gasket in there? A gasket on each side of the shims? Okay to use gaskets rather than shims, since they're easier to cut? Sure is a lot easier to just tighten the big nut on a full-floating axle until all the slop is out of the bearings, and then bend the tab over.

This doesn't seem like a very good design for lots of reasons. First, the shaft has to carry the weight of the vehicle as well as transmit torque. Second, the key and keyway carry all the torque and are weak compared to a one-piece forged shaft. My key sheared off and the keyways in both hub and shaft were so bunged up I had to scrap them. Third, it looks like a hassle to get the bearing preload right.

Anyway, I'd appreciate if anyone who has set up one of those 8-3/4 rear ends can tell me how to do it.



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