Athearn SD45 Derailing Problem


New Member
I just bought another SD45, having two SD45's already. The problem is that the new SD45 seems to derail at certain parts of the layout while the other two don't.
I cleaned the track but I know it isn't the track.
Upon reversing, the problem SD45 made a slight grinding noise, along with a thudding noise. I opened it up and immediately noticed that the piece that holds down the worm gear wasn't properly seated. It was relatively difficult to re-seat the clip. What caught my attention that the lubricant was black.
I can't return the loco since I accidentally increased its issue by forgetting that I took off the shell screws and in preventing-collision mode, picked it up, breaking a couple of wires. But as I really like the shell, I'd rather keep it as a project in learning more on how to repair Athearn locomotives.
My questions are: how risky is taking apart the truck or should I switch the front trunk with its back truck first. And are there exact measurement standards for the drive shafts as I quieted the knocking noise by decreasing the spacing on drive shafts parts? Could the wheel set be misaligned?
I would put it back together and see if the problem cleared. Make sure none of the wires are binding the trucks while you put it back together. Sometimes giving it a once over is all it takes.
After thinking about it some more and running the loco this morning, I also noticed that it makes an odd clicking noise when I move the front truck for a right turn. Binding on something perhaps. The other item is that after snapping some of the wires, I also noticed that there are very short but whether they are too short probably isn't the problem. It is only when the loco is turning right, then the very front left wheel leaves the track, mayhem and embarrassment ensue.
I hope it isn't the cynic in me, but perhaps the choice of the black grease was deliberate to hide a defect in one of the gears involved. If it has a chip or flash, or a gouge or a broken tooth, it is very possible that it may click or clunk only when the truck is turned in one presents one working face of the gears that may not be presented when the truck is facing fully forward or in the other direction.

I would think a careful inspection to make sure no wires are being pressed against any of the drive components when the shell is in place would be a good place to start. Cleaning the drive and having a good look under strong light and with an Opti-Visor would be next. I haven't personally had a broken gear problem yet (only two modern diesels in my roster), but they do seem to plague the industry the past five years. In one of those modern diesels, though, I did have to displace a wire that was pressed against the truck when the shell was in place. Unless there is a bit of grit in one of the axle end-bearings, I think your clunk will be attributable to one of these two problems, gear or wire.

If the wires going from your trucks to the board are too short, the truck will bind because the lack of slack will prevent a full range of motion (not just up and down, but left and right too).

Does it derail in both directions? Have you checked to make sure the wheels are in gage? Does it still have its weights in the front and rear?
Thanks for all the advice. I solved the derailing problem a few hours ago.
When I accidentally broke several of the wires, I did slop job soldering which was the cause the tapping noise in the shell when I turned it to make a right turn. I re-soldered it with a better connection.
Secondly, I discovered the curve causing the problem was binding the front truck was out of line. The reason my other locos didn't derail is because they are dirty, sticking to the track. I just bright-boy'ed the whole track.
here is what I am doing right now: