Noisy Atlas MP15DC with DCC

[Ogden Rails]

I have two of the subject locos and both are noisy in operation. Both units are new with very little operation time.
The noise is hard to describe but it is like an intermittent scrappy sound. It is more noticeable at mid to high speed, and not so loud at very low speed, and occurs whether operating on straight or curved track.

I have completely dismantled both mechanisms and checked the drive train from motor, universal joints, to trucks by installing each component one at a time and checking noise level. I have also cleaned the universals, worm gear and trucks and relubricated the worm gear and trucks.

Noise level was not noticeable until one or both trucks were installed, so must assume the noise is being produced by the worm to truck gear meshing.
I noticed that the trucks seem to be quite a loose fit in the chassis. I have pushed the trucks up as far I can in the chassis and tightened the screws holding the chassis halves together. However, the trucks can still be easily removed with a gentle pull.
Inspection of the trucks, particularly the retaining lugs at the top, reveal no damage.

Has anyone else in the group had a similar problem?
Thanks,
John

[Steveruger45]

When you had the trucks out of the chassis did he wheels and gears roll and turn freely?
I mean, put the truck on a smooth flat surface or a piece of track and gentle push it along without putting on any down pressure.

[tehachapifan]

I have 3 but all run quietly. That said, it appears that the Atlas MP15DC is on the list of locos that can possibly benefit from the Bearden trick as can be seen at https://www.therailwire.net/forum/index.php?topic=48052.0

[Ogden Rails]

Thanks for the replies.

Steve, both trucks roll and gears rotate with no problems.

Rus, my locos looks like a candidate for the Bearden trick.

I did forget to mention that there is quite a lot of axial movement of both worms / shaft assemblies within their bearing blocks.

John

[Steveruger45]

John
Ah ha.  Yes try to adjust the axial slop in the worms down just enough not to bind.  Check no flash or burrs are on the universals ball and socket too and lightly lube these.
Let us know how you get on.

[tehachapifan]

Yes, while my MP15DC's were never noisy, I did have at least one that I believe had this (excessive?) axial play that was causing a sort of rhythmic hard braking and lunging-type movement when going down a fairly steep section on my branchline (probably had more to do with the perhaps overly steep grade than a loco design shortcoming). I think this was caused by the worm moving up against the bearing blocks harder than on level track for whatever reason. I seem to recall adjusting the play in the worms and I think it helped. I do recall the rhythmic movement initially becoming more rapid but less pronounced, then I think it continued to smooth out with continued running. All this said, I guess I'm still not exactly sure what was really going on with that.

[Ogden Rails]

Both locos have benefited from the Bearden trick.
Noise is considerably reduced across the previously noisy mid to high speed range. Low speed range was always okay.
Thanks Steve and Rus for your suggestions.
John