My Centennial 2000 SD-90 Item 6-18268 has one motor that is much weaker than the other. When "bench testing" I can stop it with the slightest finger pressure. Any advice or suggestions will be greatly appreciated. If not for this forum I wouldn't have any trains running! Thanks to everyone for their help and support.
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Is it a new brand new engine? If so send it back for warranty repair. Sounds like a circuit board is bad, had that happen with a K-Line MP-15 and it kept derailing as one motor went extremely fast and the other just creeped along, so I sent it in for repair.
Lee Fritz
Is that the only performance issue? What voltage setting when you can stop it?
It is not the circuit board. Both motors fed from same source.
One motor has a tach and if you try to stop it, the circuit senses the slow down and raises voltage to maintain ordered speed. So that motor would be hard to stop.
The other motor is a slave with no speed sensor. So if you stop it, the board doesn't know it and voltage is not raised since the tach motor is still spinning.
Try stopping both motors with the same finger pressure. Most likely neither will stop or both will stop and you will have created a stall. DO NOT do that for long.
If in fact one motor is stopping much sooner and doesn't work the same. Check the truck for binding first. Otherwise a motor can be bad and needs to be replaced.
But I doubt that is the issue.
IF they both start about the same voltage and stop together when you lower voltage most likely all is well. G
George is right, I doubt there's anything wrong with the motor. This is standard for speed controlled locomotives, the uncontrolled motor doesn't seem to have any torque when free running. Not to worry, when it's on the track, it'll perform fine. 
The slave motor is the one that seems really weak. They do not start together on the bench test. The slave needs a good bit more power to get started and stops much sooner when lowering power. On the track is when I really see the problem. Lots of jerking, jumping and stalling on less than perfect track like radius and switches. Thanks for your help. Any other ideas will be greatly appreciated and investigated! I do like to run this engine with a consist of Blue and Orange. Fits nice on display but nothing else looks good pulling that consist.
Seems to be solved. Bad solder connection at motor terminal and a stuck/stiff pickup roller. Thank-you!
Bad connections would certainly have an effect! 
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