High boiler 10-wheeler binding issue

[trainman203]

My friend has one of the high boiler 10 wheelers that Bachmann discontinued many long years ago. This one had not run in years, 10 or 12 at least.

I provided a full service lubrication on all rods with light oil and on the driver gear with some Labella light grease, very small applications of each. Plus, a droplet of oil on each axle bearing.

Running forward, performance is perfect, smooth as silk and purring like a kitten. In reverse, performance is smooth, but there is an intermittent snag that cannot be predicted when it will happen. It is, however, always at the same point of the driver revolution. Sometimes it catches hard enough to stop the engine .

The only thing is, though, when you block the engine up to spin the wheels in reverse in traditional time-tested run-in method, the snag disappears. The wheel spin, just as smoothly and perfectly when blocked up as when running forward.

I know for certain that the problem is between the driver axle gear and the worm gear. Some type of axle slack is allowing it to be pushed up too firmly into the worm gear when the engines weight  pushes it up. I am very reluctant to disassemble this engine to look at this problem head on. 

Has anyone else ever had this happen before? If so, what did you do about it? Please report. This engine is nowhere to be found used anywhere anymore, so we can't replace it. Besides, it is a beautifully done custom decal job.

[trainman203]

 It could be that a little piece of old dried lubricant might be jammed up between one or two of the teeth of the axle gear.  Or even a little particle of ballast. When the weight is off of the engine, the gear drops down in vertical slack just enough so that the worm gear misses it, and smooth rotation occurs. When the engines weight pushes the gear back up a little bit, enough for the worm to be hitting whatever is lodged between the teeth, we get interference. This seems like the most logical problem to me.

I believe I can fix this, but I'll have to take the bottom retainer plate off and take the drivers out of the frame. Then go around and with a wood toothpick clean between every tooth on the axle gear. This may or may not fix the problem, but it seems like the most logical place to start.

Anyone have any comments about this?