Kato SD 40 problem

Model Railroader General Discussion (Model Railroader)
1

I have 2 N scale Kato SD40 locos that have developed the same problem. The other night I was running my trains and my Kato SD 40 was running great, as always, when all of a sudden it started making a thump-thump noise. I watched it very closely as it went along the tracks and found that the front wheels on the rear truck are coming up off the tracks and falling back down on the tracks about every inch or so, thus making a thump noise. It only does it when the loco is on the rails, I can lift the rear wheels off the track and leave the front truck on the rails and it runs smooth. I removed the rear truck and everything looks normal except there seems to be no lube on the gears, I lightly lubed them and the problem is still there.

A few months ago I was running the other Kato SD 40 and it started doing the same thing on the same truck. These are excellent little locos when they run. Anyone experience this type of problem, It acts like there is a binding somewhere. Any suggestions as to where I should start looking for a solution?

2

The only thing that I can think of is there may be a small piece of ballast (or something) in between a couple of the teeth on a gear. If the piece is small enough, when you pick the loco up off the rear truck, this might give the gears enough clearance to miss the ballast.

You might remove the truck and see how it rolls by itself on a piece of track. This will help narrow down what the problem is.

3

Check the gear train in each set of trucks for “lint” packed in usually with grease. This forms a hard to see bump or rough spot on the gears which caused the same response on mine.