GS4 Lurches Downhill

[wcohen]

Hello All,

I've searched the archives and have not found this question addressed.  If it has and I missed it, I apologize in advance.

I have a current production GS4 (purchased new a few months ago) and it's really a great value.  It runs fine on relatively level track at home, but when I bring it to my model railroad club it bucks and lurches downhill - especially when pulling a train.  For those of you who have not experienced this, older Athearn and P2K diesels and brass steamers have this problem too.  The solution for those models is to add shims to the worm shaft to eliminate excess play. It fixes the problem every time.  Now, here's how this relates to the Bachmann GS4:

The Bachmann GS4 is constructed such that the worm is on the motor shaft and it's the motor shaft that has the excess play.  This isn't a defect, it's inherent in the design.  Short of installing a NWSL gearbox (that would probably require milling the frame), has anyone discovered a fix for this situation?

Please don't take this as a "knock" against this product - I think it's an excellent value for the money.  My son loves it keeps him from wanting to run my brass GS4s on his railroad.  Maybe I'm asking it to do more than it was designed to do.  Any advice would be greatly appreciated.

Wayne Cohen
Morgan Hill, CA

[Jim Banner]

Wayne,
As you have already figured out, you need to reduce the end play of the shaft the worm is mounted on.  In this case, that is the motor shaft.  Sometimes you can add a brass bracket that restricts longitudinal motion of the motor shaft.  Usually, it does not matter which end.  But if you want to be sure, add it to the end of the motor toward which the armature is pushed when the weight of the train pushes the locomotive forward going down hill.  Alternately, you can measure the axial free play of the motor and make up a spacer a few thousands of an inch shorter.  Installing the spacer at the brush end of the motor shaft usually is the best bet as it is usually the end cap next to the brushes which is removeable.  This method requires some special tools, including a lathe, and taking apart the motor is not for the faint of heart.

There are some other methods that might work and are worth a try.  One is to lubricate the worm and its pinion with gear oil (I like Labelle #102 for this job but #106 will also work if that is what you have on hand.)  And second is to break in the worm and pinion by running in reverse, pushing a train backwards around your layout for a few hours.  Clean and re-lubricate the worm and pinion at the end of that time.

If all else fails, you might want to try holding the train back a bit by providing a bit more friction.  A tiny bit of leather or cork or even dryer lint  in one or more journals of the caboose truck can help.
Hopefully, others will also write about their favourite methods of stopping or at least reducing this annoying action.

Jim

[wcohen]

Thank you for the info Jim.  What I need are "U" shaped shims that somehow won't fall out.  Maybe some sort of bracket (as you suggest) might do the trick.  Pulling the flywheel and worm and then taking the motor apart doesn't thrill me.  I'll keep the group posted.