Walthers FB-1 running poorly but only in one direction

[cnj1524]

You can get every part you need from NWSL,did you check the gauge of the wheels to see if axle is bent?and do the working trucks have play in the worm gear?

[Backshophoss]

That cracked shaft coupling is the cause of the problem,seems to be a common problem of models produced
in China, the coupling,after being seated,passes a "QC" test, then "Cracks" after assembly at the factory
All it takes is a minor defect in the plastic part to cause the problem.

[Snowmojoe]

Unfortunately, the cracked yoke can't be the source of the original problem, because the cracked yoke was actually in the Erie, which was running just fine despite the cracked yoke. However, now that I know it's there, I've obviously got to do something about it.

The working trucks did have some play in the worm gear. Should I shim out the worm gear shaft to take out the slack?

The axles do not seem bent or anything - they rolled pretty true when I checked them, but I don't have any other way to check them right now.

[Backshophoss]

There should be a little "play" at the worm gear,Athearn uses washers to minimize "play" at the worm.
Check with Walters if you can get a replacement worm gear.
Would clean and check the gears for dirt/grit,then rebuild the truck with a tiny amount of grease/oil,
there's a bit too much white grease on the truck now,will only attract dirt/grit

[cnj1524]

you can always take 1 part at a time from bad truck to working truck,may take some time,maybe a beer or 6 then hope you discover what part
is bad,trouble shooting does not always come easy,if you really like the unit I recommend NWSL wheels n gears,what a change it will make,very
smooth,nickel wheels for better pickup