SD40-2 wobble

[lv4142003]

I have 4 SD40-2's and they all have a bit of a wobble. Anyone else have this and is there a fix?

[jward]

on most if not all Bachmann diesels there is a bolster screw, similar to that on a freight car. you can tighten this screw to eliminate wobble, or loosen it of your locomotive doesn't track well. look on the chassis just above the gear tower at each end and you should find these screws.

[K487]

iv4142003

At least some of my Bachmann HO SD40-2s' truck/gear tower units are press-fitted to the metal body.  Whether press-fitted or screwed in, a check to see if they are installed properly might be helpful.

Also, remove the loco shell (so you won't bend the horns, and it's easier to balance up-side down), lay the loco on its back, remove the snap-on truck bottom plates with a small flat-heat screw driver tip, then connect a couple of wires and run the motor  slowly while watching the wheels and gears turn and checking for any wobbles.  I've done this to all of my SD40-2s and have never found a wobble (good engineering and production - I'm impressed.)

Consider too that sometimes a surging action of the loco when moving can, especially at slow speeds, imitate wobbling.  My guess is that any surging is caused by the two T drive shafts* (one on each end of the motor, connecting the motor drive system to the gear towers) that are not quite straight (I've seen some straight shafts and some bowed ones on my engines.) 

* As info Caboose Hobbies has a paragraph on their site basically stating that model train engines run smoother if the two Ts on the ends of the drive shaft are not parallel (like Bachmann's) but at 90 degrees to each other.  To me that makes sense.  Of course if the shaft itself is bent that would probably negate 90 degree advantage and/or exaggerate the problem.

I wish Bachmann would use the drive trains that are used on another brand - these plastic drive trains look AND function like they were machined (maybe they are), and in my thinking are key to making the locos run smoooooooth. This would increase the price (hopefully just a little bit spread out over a 10,000? thousand engine production run) but I think it would be worth it.

Extensive running-in new locos usually helps a lot on getting them to run smooth(er).

If your problem is significant enough contact Bachmann.

Hope this is helpful.

K487

[jward]

some clarification about the bolster screw.

on many of the diesels, there is a plastic plate which is screwed into the top of the gear tower.     this plastic plate is held in place by the chassis, and fits into slots in the frame halves. this is true whether a vertical split frame like the sd45, or one with upper and lower halves like a gp40 or b23-7. the plate should be held firm, and by adjusting the bolster screw, you can adjust the amount of wobble in the truck.