USAT split axle problems

Wheels slipping on "axles"

USAT diesels have a common problem with wheels slipping on the axles. Looking inside, the axle assembly consists of 2 "half shafts" pressed into a hollow plastic casting that has the gear. Each half axle is a metal shaft pressed into a wheel.

Again this plastic casting is a tube that has the worm gear cast as part of it, and the two wheel/axle "half axles" press into this casting.

When the "wheels slip", it's really because one or more axles are spinning in the tubular casting, which has split and lets the "wheels slip".

Either the plastic is too brittle, or the clearance between the knurled end of the axles and the nylon is too close or whatever. Does not matter, for as long as I have been in the hobby, they split, even just sitting brand new in the box on a shelf.

USA claims to have fixed the problem a while ago, 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" also. 

Call USA and they will send you new axles if your loco is still under warranty.

Do I have the problem?:

Put the loco on it's back, then put one thumb on each wheel of the SAME axle, and try to rotate the wheels in the opposite direction... if either wheel is loose on gear casting, it will turn. Use firm pressure, but don't go all sasquatch on it. Remember that these locos put out a lot of torque by themselves.

To repair:

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".

You can also find some K&S brass tubing that is close enough in size. The K&S stock number is 9828.

Another way to repair is to remove the axle, wind monofiliment fish line around the end, coat in epoxy.

I use an inexpensive press from Harbor Freight to do this.

See THIS page to see the press, scroll down. It makes it very easy and safe to press wheels on and off.

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.


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