Gentlemen, I have recently acquired one of these beasts, and it's giving me a bit of a problem. It was new in the box.
It's not a terribly smooth runner but I don't expect too much out of what is basically a glorified 736, however it slows drastically around curves, sometimes outright stopping. This is with only the tender behind it.
I already took it apart and checked for the dreaded motor bearing problem, and the motor is definitely NOT the problem. For one, the armature has no side to side slop and very little front to back - the armature doesn't contact the rear casting nor does it touch the brushplate.
The issue is CLEARLY in the chassis, as when rolling the motorless chassis down the track, the force required to push it is somewhat uneven, varying as the wheels turn. Just like when it's under power, rolling the chassis into a turn practically causes a dead stop.
-The rods do not seem to be causing the problem. There's nothing bent nor clamped down tight.
-The driving wheels appear to all be in quarter.
-The rear driving axle has very little (almost imperceptible) side play, while the front three axles all move side to side a small amount.
-Sometimes spinning the rear wheels (locomotive fully assembled) by hand they will hit a spot where they will stop, if I reverse direction they will open up and then I can resume spinning them.
Any of you repair guys have any suggestions?
ETA: I have also lubed the locomotive.