S4 (S2) traction loss

[DAVE2744]

My 1 year old S4 switcher was loosing 60% of it's original traction in one direction, and about 40% loss in the other direction.  Still ran smooth as silk.  My track is absolutely clean, as are all my loco wheels.  I was looking for a cause that would be dependent on direction.  It also only manifested itself when pulling several cars vs. only a couple.  Disassembled loco.  Couplings, shafting, worm gear all perfect & tight.  Gears all seemed OK.  Put a screw driver blade against teeth on first gear (next to worm), and pushed truck along.  I noticed the second gear down from the worm was jumping teeth.  Rotating wheels (with worm disconnected), all gears appeared perfect. No cracks, no damaged teeth, no dirt).  I did noticed one of the "pin" type gear shafts was not even with the outside of the truck's gear case.  Out about 1/32". Pushed the shaft in so both ends were flush with outside of gear case.  Problem solved.  These shafts are only retained by "force fit" into the gear case. Upon running the loco again, I noticed the very slight gear grumble the loco always had, one direction only, was now gone.  The sound system was masking this clue.

Apparently the wall thickness of the gear case does not allow for any movement of the gear pin axles before it causes problems with gear mesh.

This problem would apply to S2 and S4 models as they share same truck assembly.  Just thought this might be useful to others with these engines. 

They are real smooth running models.

[jbrock27]

As one searching for one, in analog, I thank you

[electrical whiz kid]

Check to make sure that ALL your wheels are making good contact with the rail.  Consider that HO scale locomotives; diesels in particular, need all of the help they can get in this department, as they will tend toward light-ness.  I don't care how smoothly it starts and stops, etc.; if you do not have all of the wheels squarely planted on [top of] the rails, it won't pull worth a lick.
Part of my tool compliment is a granite b lock I scrounged from a factory, that trams out to near perfection; and using this to check square-ness works like gangbusters.  Using a feeler gauge with this block will work as well.  There should be NO air between the wheel and the block.
When a locomotive is running on the track, you will probably not get full contact at all times; usually due to lousy track-work, crud on the tack, etc.; so this test would be pretty essential.

Rich C.