I have found the problem and it is quite an embarrassment. I have installed 2 wirewound resistors to lower the voltage going to the motor to make the MTH smoke unit I installed smoke adequately. These are located just in front of the weight. Additionally, I mounted a 15 volt voltage regulator to the weight to use it as a heat sink. This made the weight electrically active with a negative charge. Apparently the weight would shift slightly and touch the resistor wire. It only came into play with the DC polarity was right. In this case the forward running condition. Grinding the weight slightly corrected the problem.

Thanks for all your attempts to help.

Rich

I admit, this is a strange one.

I have performed bench testing with leads connected to pilot trucks, arrow forward. No improvement.
Touched leads to all four drivers. No improvement.
Removed bottom cover and attached leads to motor plugs. No improvement.

Motor in the forward rotation will not turn the worm gear enough to move the armature shaft from one end of the motor to the other.

I think I have revision 5 drive. Gear bulge is offset.
I remain puzzled.

Thanks,
Rich

I have a hardly used 10 wheeler that runs like a champ in reverse but will not run in the forward direction. The motor just hums and the drivers creep. Two different transformers yield the same results. There does not appear to be any binding in the drivetrain. Any ideas on how to fix the problem would be welcomed.   

Thanks,
Rich

Thanks for the photos. I did not think it was possible.

Just bought a 10th anniversary "Annie" 4-6-0. Quite impressive detail.

Came with engineer and fireman figures. How in the world do you get the engineer in the cab?

I am trying to remove the boiler and cab from the chassis of a bumble bee Big Hauler. It has a red switch at the back of the cab that prohibits the cab from being removed. Does anyone know how to remove the red cap off the switch to facilitate disassembly:

Thanks,

amflyer1

Thanks to the both of you for your quick response. It helped a bunch.

Does anyone know how to disassemble a battery lit G scale coach to replace the bulbs? I have removed all the proper screws in the undercarriage but the brass conductors seem to be holding the floorpan to the body. I don't want to force it.