USAT Alco PA-1, PB-1



These are very nice models of the Alco PA-1 and PB-1 units. There are/were available in road numbers 51 and 52. 

They have great detailing, and are handsome locomotives.


Pick them up from the bottom, holding them on the sides can damage the fine grillwork.

Run them on the layout carefully the first time, they are pretty long! Check your clearances.

Drive system:

They have standard USAT 3 axle trucks. The motor block holds 2 axles, and the 3rd, "outer" are hinged to swivel side to side. Some people have had problems with this, and others have no problems at all. I'm in the no problems at all camp. I did discover something that could explain people's problems, see the tips section.

The wheels are are 1.376" in diameter (measured near to the flange, which scales out to almost exactly 40 inches.

The smoke units have small motors, and a separate regulator/controller board. Use 25-30 drops of smoke fluid. They should run about 20 minutes. They do have auto shutdown, but the manual says to turn them off if you run the loco without smoke fluid. Good idea.

Lubrication: be sure to lube the axles (I would use a gel grease or heavy oil). Lube the ends of the axles well, since the power is conducted there (only 2 of the 3 axles on each truck).

You can lube the gearbox after every 100 hours of operation, remove the bottom of the gear box and use a good quality grease.. 


First: pay attention to the different screw sizes:

  • The 10 body screws are the longest and thinnest
    The 4 screws that hold the nose piece are larger diameter, and shorter than the "body screws"
    The coupler pedestal screws (which do not have to be removed) are short, and the same diameter as the nose piece screws.

Lay the loco on it's back.

On the A unit, remove the nose piece with 4 screws.

Remove the fuel tank with 2 screws.

I remove the the 2 fuel tank skirts, pull straight up gently, the grab bars stay on the loco. Note that the tank holds these skirts in place. They will only go back one way, so don't worry about getting the left and right sides mixed up.I remove them to avoid damage later.

Remove the screws from the 4 foot "stirrups". Use a small flat blade screwdriver between the stirrup and the body. Do this gently and you will not damage the paint.I prefer not to remove the handrails from the body, because it often damages the point.

Your are left with 10 deeply set screws to remove and the entire chassis will lift out. It's easier to have the loco on it's back or at a 45 degree angle when doing this. Be sure to unplug the smoke unit wire and the headlight connector. Make sure you find all 10 screws!

Mark the front of the chassis inside on the weight on B units, so you do not put them back together backwards.

Reassembly is the reverse. On the A unit, make sure the front part of the chassis sets down below the body sides or you will never get the nose piece back on. Just put in the 2 chassis screws in the front, not the rest of the 8. Once the chassis drops down in place, then you can put the rest of the screws in. 

Disassembling the trucks:

To remove the cover that goes over the main gearbox, remove 6 screws and lift the cover off. Notice how the brass bearings are aligned. They fit in a slot in the housing. It's easy to not get them in place. The brass bearings need to have one of the points pointing straight up. This is VERY important. Many people destroy these after taking them apart, and not getting the bearings back right will not allow the gear mesh to be right, and you WILL destroy the gears.

Here's my tip: (I did this after swapping out the wheelsets with traction tires for "solid" ones).

Get the axles pretty much in place. Align the bearings so they are centered in their slots on the sides of the motor block.

Try to get the points up on the end nearest the fuel tank. Now put something small under the motor block at this end, on each side. Something around 1/4" works. These will push the motor block up towards you and help seat the axle and keep the bushing from rotating. Look VERY carefully to see the bushing is in the right place. When properly placed, it will have very little play in either direction.

Now do the same thing to the next axle away from the fuel tank. Once you have all 4 bushings in place, the 4 shims under the truck will keep the bushings from coming loose when you put the cover on.

Put the cover on very carefully, and put the screws in gently, so you do not disturb anything. As usual, make sure you find the original threads, and I lube the screws with Armorall to keep the plastic from wearing out.


If you buy some JST 2 pin connectors, you can just unplug the trucks from the main board. The connectors with 4 wires are track pickups, and the connectors with only 2 wires are the motors.

I'll describe the polarities, but you SHOULD ALWAYS check the track pickups with a meter.

Rear truck right rail is black, left rail is red.
Front truck right rail is red, left rail is black.
Rear truck motor + is black, motor - is red
Front truck motor + is red, motor - is black


Tips and modifications:


The Kadee site does not list a conversion for the PA/PB, but the coupler pedestal looks very similar to the F units, which use an 831.

On the F units, there is a second hole in the coupler "tang" and you trim the end of of the tang to allow the hole in the 831 to align with the pre-drilled hole in the tang (which is not the hole that is used for the pivot).

There is no such second hole in the PA's tang. I need to measure the coupler location to see where to mount the 831. So far, I have let them stick out quite a bit, and aligned the "button" on the tang with the circular depression on the coupler body. They are a bit far out, but it looks if I mount them in the original hole and trim the tang, the front coupler will interfere with the pilot.


Many people have replaced the traction tire wheels with solid wheels and removed the sliders. (replace the R22-519 with R22-518) I have done this on all my F units, and it reduces cracked axles and increases pickup, so you can do without the unsightly sliders. This does reduce traction a bit, but these locos were designed to MU, and an ABBA combo looks great.

R22-518 Metal Wheels With Gears (2) (for center axle of the 3 axles)

R22-519 Traction Wheels W/Gears (2) (for the "inner" axle comes with traction tires - axle closest to the fuel tank)

R22-520 Metal Wheels With Gears (2) (for the separate/outer "floppy" gearbox/axle)

Swiveling/floppy axle problems:

Some people have tremendous problems with the swiveling outer axles, picking points is the most common complaint. Others have absolutely no problems.

I would ensure that the spring/suspension mechanism in the chassis is lubricated, but I believe the people having problems have bad trackwork, either gauge issues, or vertical transitions.

Some people have bolted a plate on the bottom of the motor block to lock the swiveling axle, but of course it restricts the minimum radius, the whole reason the mechanism was designed.

Recently I think I found the reason for the complaint: The swiveling axle has a pin in the top of it's separate motor block. This pin slides in a curved groove in a chromed metal plate to guide it.

I noticed mine were very hard to move. The metal plate is not real smooth. I put some moly grease on the plate and worked it back and forth, it made a huge difference in the ease of swiveling. Now, if this took a lot of effort when the loco was laying on it's back with no pressure other than gravity, just think how much worse it would be when the loco was pressing on it. Check this out on your loco before you swear at these trucks.

Weather Underground PWS KCACARLS78