Assistance Required with a short in an Athearn F45

[shark_jj]

I was installing decoders in 3 Athearn F45's I recently acquired.  Digitrax DN163K1C's.  The first two went swimmingly. Which is an interesting choice of words since these units were never taken out of their boxes and they are swimming in lubricant.  That's a separate issue.  Unit #3.  Shell off.  Decoder installed.  Test run.  It was fine.  Back to the work bench, notice the frame seemed a bit loose.  Gave it about a half turn to tighten the screws.  Placed the shell on.  Installed MT couplers.  Put it back on the track.  Dead short.   Ok.  Back to step one.  Remove the couplers.  Test it.  Still a short.  Remove the shell.  Test it.  Still a short.  Back off the screws half a turn to loosen the frame.  Test it.  Still a short.  Now we were completely back to where I started. 

My assumption was that I had something making contact between the frame halves.  Took the frame apart.  Nothing obvious other than a lot of lubricating oil. Putting the frame back together.  Visual observation showed no part of the frame touching the other side.   Using jumpers with alligator clips I applied track power to each side of the frame.  No short.  That left only the trucks. 

I applied power to both sides of the front truck.  No short.  Applied power to both sides of the rear truck.  Dead short.  So, by process of elimination the problem was in the rear truck.  Since everything appears to be plastic with the exception of the wheels themselves the only thing I can think of is that one of the wheels is in the truck backwards with its insulated side on the opposite side to the other 2.  I can't imagine what else unless someone can point me in an other direction.  I'm not sure why it didn't short right away when I did the install of the decoder. 

In any event, that brings me to my request for assistance.  Has anyone taken an Athearn F45 truck apart.  There is a bottom cap on the truck with what appears to be a clip.  Same as most trucks.  However when I lever the clip open, the cap doesn't move.  Something else is holding it on.  These parts are pretty fragile, so before I began prying I thought I'd see if anyone else has opened one of these up. 

Thanks for any help.

John

[jagged ben]

I think it's the wheel gauge being too narrow, and the half axles actually making contact inside the axle.  An annoying possibility on these models that I've seen once before.  You may be able to stick a screwdriver into the truck and twist to adjust the guage outward, without disassembling the truck.  The problem is not a backwards wheelset. The wheelsets are not asymmetrical.

If you do end up needing to disassemble the truck, and if I recall correctly, the sequence is to first pry off the plastic clip at one end, then carefully pry one side of the sideframes upward and then outward and downward over the side.  There are four clips on the side frames that snap onto the metal inner parts.  So first you pry the top of the sideframe up and off to undo those clips. Then bend it outward so you can rock the whole thing downward and off.  Once you free one side the other side is a similar process but goes easier.  Hope I'm making sense.  It sure feels like you are risking breaking them but I haven't broken any so far.

[jagged ben]

Oh, and while you're right that everything except the wheels appears to be plastic, those grey pieces inside the truck (split frame style) are metal that conduct the power to the frame.  Be careful of the copper wipers when reinstalling the trucks!   This mech is a relative pain to get all back together in the end.

[shark_jj]

Thanks for the insights Jagged Ben.  You were correct that the trucks were very slightly narrow in gauge.  I opened them up and gauged them correctly.  It made no difference.  Knowing that the two grey halves of the truck are metal, I suspect something is touching.  A visual inspection shows a gap between the two halves everywhere except under the plastic cap, which of course you can't see under.  Knowing the two halves are metal, not plastic, points me in the right direction.  Now I just have to work up the courage to tackle taking it apart.  Thanks for the help.