I have no experience with this particular locomotive, and minimal experience with N in general. But I have had experience with locomotives that run better in one direction than another.
I recall some steam locomotives where the motor was held to the frame with a single screw and the different torque from one direction moved the motor a small amount. Adjusting the motor mount was the solution. That is not likely to be a fix for your issue.
In the days of open frame motors a change of direction could move the armature against a bearing differently. Again not likely to be an issue with your loco.
But does anything about the gearing look different when the direction changes?
Most often the issue is the way the trucks are mounted to the frame and that there is some slop so that when the trucks are in a sense being pushed rather than pulled they are in a different alignment with the gearing, or pushes a gear against another gear in a way that nearly binds. This can be easier to see with the shell removed, standing directly over the model, and hitting the reverse switch again and again. You notice the trucks moving a bit. The fix can be a challenge. That is where the actual tech guy from Atlas may have some help but it could move things along if you looked carefully for odd movement of the trucks that varies by direction, or odd movement of the motor and gear system that varies by direction - in all cases best studied with the body removed.
Dave Nelson
Left a message detailing problem Thursday night, awaiting reply. I may just send an email to tech support if I dont hear back in a few days.
Doug,
Not sure what the other comment was (unless it was the very first part, which is totally unrealated to model trains). I beleive the High speed sound from the motor is a function of the problem, and not a separate issue. Just trying to figure out what the actual problem is. Both GP-35s run well, one needed to have the board reseated, but other than that everything is fine with those two.
Sorry for the confusion.
Edit more: the bad experience: the problem was not an atlas product. Bachmann steam and inexperience in model railroading (7 or 8 years old).
Edit: Please note that I suspect the SD7 is used (it was heavily discounted). I will probably give Don a call Mon or Wed if I haven't sovled the problem by then.
Call Atlas Tech Support and leave a message for Don Ext.7133. He is one of the N scale repair guru's and the end result might take a while, 5 to 6 weeks but worth it in the long run. He sure has helped me. Really worth the time spent.
As to your other comment on Atlas. I don't have any problems with Atlas and purchase them all the time. Note that I have been in N Scale for over thirty years and experiance is the best teacher. I have watched all the N Scale manufacturers go from lawn mower sounding equipment to really reliable models. Be sure and call Don, he can help you. Doug
First off, anyone get the paralleling pun?
I recently decided to lose my mind and do something I swore I would never do, and purchase N scale products (had a bad experience when younger). When on DC power (this one also has Lenz DCC decoder, that I have yet to run on DCC), the locomotive runs about the same speed as my two atlas GP-35s in the long hood direction. In short hood direction it runs considerably slower as if the gears where slipping. Motor RPMs sound high compared to the GP-35s in long hood direction, and extremely high in short hood direction.
Trucks appear to have the same amount of slop in either direction by finger test, and the gear in the center spins when I run the truck over my finger (separated from chassis weight.
Anyone know of a fix for this?