I've maintained my Bachmann Big Hauler locomotoive (a 4-6-0) but within the last 8-10 days, the motor has started producing occasional "whirring" and the problem seems to be getting worse. The whirring when it occurs (which isn't always) seems to be accompanied by inconsistent operation, i.e., the train speeds up and slows down with about a 1 second oscillation period. I've tried cleaning track and wheels, assuming it's an electrical contact problem, but the problem continues to be intermittent, e.g., every other time I operate the train. The only other problem that comes to mind for me is that it's a motor problem. Can you offer any advice?
Sounds like you may have a loose or possibly cracked gear somewhere inside slipping on it axle. Time for service!
-Brian
Brian nailed it, if the motor is turning and the loco is erratic then the gearbox has most likely gone away.
Give Bachmann service a call at 215-533 1600 and find out what yur options are?
Best of luck.