I have several Athearn engines, including another Trainmaster, and I have not encountered this problem before. What is the problem and cure? Thanks.
PROBABLY horizontal ‘play’ in the worm gears. A thin washer or two should correct
Good question. I’ve noticed this on old pancake motors and an open frame Mantua I’ve got. One Athearn too. I’ve pulled the motors out and powered them up alone and they still do it. Cleaned and oiled them. Checked the brushes and springs and they still did it.(???)
Don’t have an answer for you, but good question!
I can’t speak to athearn engines – but I bought an old Mantua steam locomotive at a swap meet and it ran better forward than backward and I checked the play in the bearing bushings and it seemed not to be the problem.
The problem on very close examination was that the contacts on the motor commutator had worn, more or less to the contour of the motor commutator. In reverse the commutator shifted a bit and the brushes did not make as good a contact. (Am I making myself clear here?) Solution – new brush contacts – and the problem was solved.
Dave Nelson
Dave-Thanks. Mine is new so nothings worn. I’m just going to buy an Aliance for it.
I think Athearn, in their pre-Genesis days, were desperately trying to recreate prototypical actions. Realizing the engineer must twist around to see where he’s going in reverse, he will naturally move the locomotive a little slower than when he is facing the front going forward. I believe Athearn was trying to be visionary and made all loco gearing, etc with enough burrs, slack and slop so when going in reverse, the locomotive moves slower 
Mac
The above paragraph is an example of someone with way too much time on their hands because the layout’s power pack is out for service.
Once again, Don Gibson is right on the mark . Athearn and early lLkelike ( and some others ) are notorious for this. The end play needs to be shimmed out of the worm gear so the gears maintain constant mesh. You want them to turn free but not move back and forth.
I have two of those, and just like God intended, being decorated Virginian (started undecorated), long hood IS forward. They both run the same speed in both directions. I once had two Athearn PAs that ran back to back, and I currently have two P2K E8s that run back to back, and two Spectrum H16-44s (again, long hood forward). They all run/ran the same speed in both directions. I guess I’ve been lucky as I have never experienced this problem. That is my total diesel experience.
When shimming the worm end play, just make sure you don’t shimm too tight. Should still have a slight amount. I have found that the gears themselves can have unbelievable side play in the case halves. I found that Labell106 in the case/ gear sides helped smooth out an otherwise noisey truck. These particular units had the Pearldrop treatment first. Reassembled in the exact order for any wear pattern, shimmed the worm, checked the axle/ wheel bushing alignment in the case, NWS wheelsets and repowered Can motor. These Athearn BB run like silk.
All this doesn’t nec have to be done, tweaking some of the obvious stuff first may solve the troubles and have a runner that you’re satisfied with.
If the brushes are not EXACTLY 180° apart, and commutator slot positioned perfectly, there will be a difference between the two directions of rotation. As these are creations of human endeavors, they are not exact or perfect. Generally, the variations in all the areas that affect this, will more or less cancel each other out, and the motors will run about the same speed in both directions. Sometimes the variations due to manufacturing tolerances do not cancel.
You can try swapping or rotating the brushes, replacing the brushes, or facing the brushes to tweak the angle between them. Most likely you do not have access to equipment to accurately measure the current status, nor the changes made; so you are basically shooting in the dark.
I have not tried adjusting the play in the worm gears yet; however I did clean the commutator with CRC 2-26 lubricant, and there was a noticable improvement. Following advise in a previous posts, I had purchased a can of 2-26 but had never tried it. The effect may be short lived, only time will tell, but I will experiment with this product again. Thanks for all the advise; it is always helpful and informative.