Atlas N scale 8-40C trucks binding

[mdltrn]

I'm looking for some help in troubleshooting an issue with the last run of Atlas 8-40C locomotives. Something in the drivetrain seems to bind randomly, causing the lead wheels to stop rotating, which in turn cause the trailing end of the truck to lift off the rails. The locomotive will run around the layout a couple times very smoothly, then will randomly bind at different locations. Until recently, it has just been annoying, but now the lift is so bad, that it causes the couplers to separate. Anyone else have a similar experience? Any known fixes?

Everything appears to be in place on the trucks and there is no debris in the gears. Two different units acting in this manner. Both units are relatively new with only 1-2 hours of DCC run time.

Thanks
Dave

[peteski]

The behavior of your model is surprising.  There is 1 motor driving worms at each end of the loco, Then each of he worms drives worm gear in each truck, which in turn drives the spur gears, then those drive the wheelsets. My point is that the entire mechanism is permanently coupled.  If a wheelset or even entire truck binds to the point of stopping, then that will lock up the worm preventing it from turning, which will stall the motor, thus the other truck should no longer move (everything should be stalled).

Your problem description implies that while the front truck is stalled, the rest of the mechanism (from the motor to the rear truck) is still running.
That would indicate that something related to the front truck is slipping.  Most likely one of the universal couplings either on the front motor shaft, or front worm shaft are cracked and slipping on the shaft.

I've seen that problem, but in all the locos with this problem I've worked on the loco would keep running (although laboring heavily) with the front truck simply sliding on the track with its wheels stationary.

[jagged ben]

Sounds like perhaps a gear getting caught on the truck sideframe/botttom part. 

Take the truck apart and check the sideframe/bottom part for flash.  Also check the wheel gauge and ensure that the half axles are adjusted such that when everything is put back together the gears are centered in the slots on the bottom part, not smashed up against one side.

Another possibility, unfortunately, is just poor quality control on the truck manufacturing, such that a gear inside the truck slips out of place and binds everything up.

(Peteksi I don't feel like we're reading the same post.  He said nothing about the other truck's wheels spinning, just that something in the lead truck is getting suddenly jammed hard enough to pop it off the track.  Like sticking something in the spokes of the front wheel of a bicycle. )

[ek2000]

I had an issue with the recent release of the SD 7 where the locomotive would derail on curves or turnouts as the trucks could not pivot freely. This was happening on 15 inch curves so the problem was a lot more severe than it was manifesting on my tracks. Wheel gauges were fine. Sent it to Atlas and they diagnosed the issue to be a wire getting in the way and not allowing the truck to swing freely.

Have to say the service was excellent. When I called them, I was assured the issue would be thoroughly checked and fixed. The locomotive was back in my hands within 7 days of Atlas receiving it. Several other manufacturers I've dealt with would need weeks (no complaints still).

Mentioning this from the standpoint of their customer service. If you can't figure it out, I'm sure Atlas will sort out the issue quickly.

[Steveruger45]

If these trucks are similar to those on an Atlas SD50/60 then there are nubs near the top of the truck tower that support the frame.  Check If one or both of these nubs are broken.

[martin station]

I'm looking for some help in troubleshooting an issue with the last run of Atlas 8-40C locomotives. Something in the drivetrain seems to bind randomly, causing the lead wheels to stop rotating, which in turn cause the trailing end of the truck to lift off the rails. The locomotive will run around the layout a couple times very smoothly, then will randomly bind at different locations. Until recently, it has just been annoying, but now the lift is so bad, that it causes the couplers to separate. Anyone else have a similar experience? Any known fixes?

Everything appears to be in place on the trucks and there is no debris in the gears. Two different units acting in this manner. Both units are relatively new with only 1-2 hours of DCC run time.

Thanks
Dave

Dave,
  I can't be of much help but to say that I had that same issue on the last SD26 that I had purchased. I called MBK from whom I purchased it from and even though I had never experienced such a thing, he acted as though he had dealt with this issue before. He just had me send it back for an exchange and I'm guessing they sent it back to Atlas. That being the case, you may make a call to the Atlas service department and they should be able to tell you if it's fixable or if they can send you a new truck or parts needed to fix it. I have always found them helpful and quick to ship what ever I have ordered and hopefully save you from shipping the engine back and having to wait for the repair to be completed.
Ralph

[nkalanaga]

I wonder if there could be a little piece of ballast in one of the gears?  I've had that problem with several different models, especially the Nn3/Z diesels.

[tehachapifan]

I wonder if there could be a little piece of ballast in one of the gears?  I've had that problem with several different models, especially the Nn3/Z diesels.

This was my thought. It's amazing how the tiniest speck of something can wreak havoc!

[nkalanaga]

Not surprising, though, considering the size of N scale gears and the close tolerances required for smooth running.

[mdltrn]

UPDATE:

Thank you for all of the suggestions, ideas and shared experiences. Close inspection of the truck assemblies revealed clean gears, fresh lubricant (from factory) and everything seemed to be in order. Two observations worthy of note:

1. When inspecting the locomotive at a whole, I placed it upside down on the workbench and tried to spin the wheels. They spun freely. this is with the trucks unsupported and tilted like a see-saw toward the front or back. I expected them to move slightly within the gear lash, but not turning freely. When I held the truck level (with loco still upside down) the wheels would not spin freely, as expected. I did notice some lateral movement in the gears, allowing only about half of the width of the gear to mesh with the gear of the axle. This may be something to explore further.

2. The binding of the trucks only seems to occur when the units are consisted together. When operated around the layout independently, the mechanism is smooth and quiet. However, when consisted, the units operate nicely most of the time, but with occasional binding.

This got me thinking about speed match the consist. I uncoupled the locomotives (Atlas 8-40B, 8-40C, 8-40C) and separated them by about 6" and ran them as a consist. Though each locomotive uses the same ESU decoder and CV2, CV5, CV6 are set identically, the middle unit was slightly fast and the last unit was slightly slow. I fine tuned the CV5 and CV6 to match the two 8-40Cs as close as possible. This seemed to make a huge improvement in performance and significantly *reduced* the binding. I still get some binding but not nearly as bad or as often. It seems like this helped a lot, but is perhaps no the root cause.

Here are the two 8-40Cs lashed-up with a 8-40B (out of picture, left). The direction of travel was to the right and they were shoving a 20-car train. Note the lead trucks binding and the coupler separation.


slightly closer image

[John]

Did you tighten the little screw that holds the two halves of the frame together (if it has a split frame)

[Steveruger45]

Have you tried swapping the trucks front set for rear set and see if the issue is truck dependent or truck position dependent?

[peteski]

As I explained in my initial post, the front and rear trucks are mechanically coupled through the worms, driveshafts and the motor.  The wheels on either truck should not be spinning freely (the worm engaged to the worm gear on top of each trucks gear tower prevents the trucks gears and wheels from spinning freely.

From what you describe, the truck has too much vertical play in its mount (pivot) to the chassis, allowing the worm gear in the truck to disengage from the worm.  I don't own any of those models to offer any advice on how to decrease the vertical play in the truck pivot.

As for speed matching all the locos in the consist, yes that is an important thing to do, but even in mismatched consists, if the speed mismatch is severe enough, one loco will usually spin its wheels to  pull the slower loco.  The truck behavior you see doesn't seem normal.