USAT split axle problems

Wheels slipping on axles

USAT diesels have a common problem with wheels slipping on the axles. Looking inside, it's actually that there is a wheel/half axle that slips in a "gear casting" which has the worm gear and 2 tubular extensions that the half axles press into.

When the "wheels slip", it's really because one or more axles are spinning in the tubular extensions, which have split.

Either the plastic is too brittle, or the clearance between the knurled end of the axles and the nylon is too close or whatever.

USA claims to have fixed the problem, and modified the knurling on the axle ends so as not to split them. This has reduced the problem, but not eliminated it, I have locos with the newer knurling with "split gears". 

Call USA and they will send you new axles. I put brass sleeves over the split gears and this seems to have fixed the problem. Other people have wound nylon fishing line or wire on the axles, epoxied it in place (while held tightly) and reinserted the axles.

The brass sleeves I have (and are shown below) have a length of 0.3", and an inside diameter of 0.3535".

Here's an article by Tony Walsham on how to repair:

USAT locos have a propensity to split the gear casting that the axle halves press into. This makes the wheels slip. USAT changed the knurling on the end of the shafts and says they fixed the problem, but I have seen the new style split also. Here's one way to fix them. (Photos courtesy of Tony Walsham).

Seeing the problem, the metal half axles press into the female parts of the gear casting. The casting splits, the axles spin.

Editors note: After applying the collars to each split part of the gear, be sure to press the axles in evenly. The last illustration where you press the entire assembly gives you no control over each axle... use a couple of metal bars (or flat files) under the gear and you will be able only to press one half shaft at a time, thus controlling your assembly.

First, take them apart, carefully. I found I normally can pull them apart by hand. If you have to lever them apart, do it gently.

Now put a slight chamfer on the edges where you will put the metal ferrules on, this makes it easier to install them:

Now press the ferrules on until flush with the end of the gear casting. I found a nice press at Harbor Freight to do this, but you can do it with a hammer or drill press if you are careful.

Now chamfer the inner part of the gear casting to make inserting the axles easier. I used a 45 degree countersinking tool in a drill press, but you can do it with a sharp knife also.

Now the most critical part, pressing the axles back in. I recommend a real press, if not, try a drill press. If you aren't careful, your wheels will not run true. Also, be careful to press them in to the right back to back distance, pulling them back apart without a special wheel puller is a pain.

Here is the final pressing using a drill press. Get everything straight and true. Have your wheel gauge or calipers handy.