Need Help with Atlas HO Scale U36B Running With Growl

[Chris333]

If there is a burr on the worm you can hit it with a wire wheel in a Dremel.

[davefoxx]

I can't see any difference in the two worms at all.  I didn't see any burrs, either.  So, I just ordered a worm, two bearings, four thrust washers, and gear lube directly from Atlas.  I might try the thrust washers first, to see if that solves the mystery, but I'll have the spare worm assembly, if necessary.

DFF

[davefoxx]

Is there end or side play in the bearing blocks on that worm?

I can't tell when the locomotive is assembled, but there is definitely end-to-end play on that driveline when the locomotive reverses direction.  I still think a thrust washer or two will solve the problem.  But since the shipping from Atlas wouldn't be much different whether I only ordered thrust washers or the entire assembly, I spent a couple of dollars and ordered the parts to just replace that worm AND the bearings, if necessary.

DFF

[peteski]

I can't see any difference in the two worms at all.  I didn't see any burrs, either.  So, I just ordered a worm, two bearings, four thrust washers, and gear lube directly from Atlas.  I might try the thrust washers first, to see if that solves the mystery, but I'll have the spare worm assembly, if necessary.

DFF

Fair enough, but we do know that the problem moved with the worm, so there is some sort of a difference there. You solution of replacing it seems reasonable too.

[davefoxx]

The next time I tear that locomotive down when I receive the parts from Atlas, I'll take a closer look.  There is definitely something different about that worm and/or the bearings.

DFF

[MK]

Slightly different dimensions?

[davefoxx]

I received the parts from Atlas today.  Because I was lazy, I tried adding a thrust washer on the end of the worm that didn't require pulling off the universal.  Problem fixed.  The locomotive runs smoothly in both directions now.  Yep, the problem was fixed with a twenty-five cent washer.  However, anticipating that the shipping for parts would cost five to ten dollars, I also ordered a worm, two bearings, three other thrust washers, and gear lube that I don't need.  To be honest, I'm okay with having the extra parts, since if in the long run, the problem recurs, I'll pull that entire worm/bearing assembly.

For your viewing pleasure, I present SCL No. 1776:



I'm very happy to finally have one of my favorite locomotives polishing the rails of my layout. 

DFF

[peteski]

Excellent!  Nice that you were able to fix the problem using the original parts.   I wonder of either the worm is shorter then needed or the bearings are thinner (either would explain the extra play between the bearings)?

[davefoxx]

I'm not sure, and, unfortunately, I don't have a micrometer.  But, one of your theories has to be correct.  Why else would the standard arrangement be one thrust washer on each end of the worm, but this particular worm required two on one end?  At least it was on the end that was easy to get to.    Thinking about it, I wonder if the worm is not pressed onto its shaft far enough?

Oh, and let me tell you, yesterday, I impatiently speed-matched this U36B before the problem was corrected.  When it was MUed with another locomotive, the slight difference in the two engines really highlighted that driveline problem.  It growled in both directions!  Tonight, with the addition of one thrust washer, it purrs and is running beautifully with my SCL GP40.  I didn't even have to speed-match it again!

DFF