Part deux....

At this point I searched the MRH site and found a myriad of topics over the years where other people were experiencing the same thing and used some very creative ingenuity to solve the problem - most of which involved adding wipers to the wheels.

What I found is that the electrical continuity issue comes down to the fact that the design of each truck takes the electrical pick-up from three axles and funnels them through a single grommet/rivet that connects to a metal plate on the inside of the plastic gearbox. That plate has the tab the electrical pick-up wire is attached to. Additionally, the wall of the plastic gearbox is sandwiched between these two metal plates - an insulator!. Who thought that was a good idea? So, if the grommet is not making good electrical contact (via loose or dirty surfaces) with these two metal plates, you are hosed. Like I was!

Here's an excerpt from Athearn's Parts Explosion to illustrate my point:

• The pink circled item is the single grommet and only electrically conductive item connecting the two metal plates.
• The blue circled item is the metal sideframe that the three axle's square, bronze bearings rest in.
• The green circled item is the metal plate on the inside of the plastic gearbox that has the tab (on top) for the electrical pick-up wire.

Instead of adding wipers to each wheel, I elected to drill a small hole in the metal sideframe, solder a small jumper wire into that hole, and then solder the other end of that jumper wire to the pick-up wire tab thereby completely circumventing the grommet. Attached is a photo of the truck showing the jumper wire in place but not yet soldered.

After doing both sides of each truck I'm happy to report the electrical continuity problem disappeared - which to me pretty much proves the grommet to be the root cause...

Had the same problem

Also had the same problem with a couple (maybe 3) of my SD40T-2's. At the time I even remember thinking they were all on the same end, though now I couldn't tell you which it was.   My fix was to sand the paint off and solder the grommet to the metal sideframe. Based on the % of them I had that needed repair I always wondered how many others had the same issue.

The other issue I had with them was they didn't run as smoothly as expected.  To resolve that I replaced all the gears in the truck (but not the wheelsets) and now they all look like they glide.  Apparently a bad run of truck parts.

Mike

Whose gears?

Hey Mike - who's replacement gears did you use?

I have two more to do and and might as well get after those as well.

Thanks!

So, in some sense, you

So, in some sense, you converted your RTR over to the way people would wire up a BB. By soldering direct to the metal side frames. 

Good Subject Title

@ espeelark

Good title to your discussion,...glad you didn't refer to that PARTICULAR Athearn loco you experienced the problem with, as this problem could have much broader possibilities across their range of locos.
 

Would be interesting to hear from others that might have experienced this same problem.

I just used new Athearn

I just used new Athearn gears.  My local hobby shop carries them.  These here poor runners when I got them, could be why at that time they were so cheap.  I have a SD38 that exhibits many of the same issues, but I sense a new motor will have to part of the process for that unit.  I bought some of the 2016 SD40T-2 RTR  run and they ran perfect, so it seems like the earlier the more likely the problem.

Mike

I also want to add...

...that I removed the chemically blackened surface from the edge faces of the metal sideframe where the square, brass axle bearings/bushings rest. I used a very fine sanding board to do that. That chemical blackener acts like an insulator and needs to be removed.

That's a really good point...

Paul, that's a really good point.  The black paint was laid on so thick the grommet couldn't conduct current and it was on those surfaces too.  I used some emery cloth and a small slotted screwdriver (to scrape the corners) to clean up those areas. 

Again, that's a really good point that Paul shared!

Mike

Too much black paint

Too much of the black paint or chemical blackener (whichever it is) is a definite problem on many RTR Athearns.  The first run of RS3s were really plagued by this.  At the very least it needs to be removed from the axle bearing slots.  It could also interfere with the brass rivet/grommet.  Lastly, it might be on either the truck or frame bolster surfaces.  As Paul said it's an insulator and must be removed.

Another issue to check on newer Athearn RTR engines is the screw-tightened motor mounts.  If they are screwed in too tight or not equally tight they can twist the motor slightly and really degrade its performance.  If I find an engine that seems to be dragging, the first thing I do is loosen the motor mount screws a half turn or so.

Scott Chatfield

Problematic blackening

I've encountered numerous examples of chemical blackening causing continuity problems.  Often it is on the wheels, I guess I shouldn't find it surprising that Athearn's blackened pickup sideframes can also suffer from the same issues!  In the case of the wheels, the problem diminishes as the blackening wears (or is polished) off.

Thanks, Scott, for the tip on the motor mounts!

-Fuzzy