I have a handful of the Atlas C628/630 locos and I love them, but like many I had the male universals crack leaving them as yard queens until I could fix them. I know some simply used glue on the universal and shaft, but that didn't work for me. I ordered new ones and actually cracked one putting it on the motor shaft. I thought about swapping out the flywheels with ones that have the hexagonal interiors to allow for a different drive shaft. I actually had a spare set, but I have ruined motors before and decided against the swap. I got looking at the drive train design and at others and saw the potential provided by the old Atlas/Kato RS3/11 drives (probably others too). Those drives have "fingered" universals with one on the motor shaft and the other on the drive shaft to the universal. I ended up using these older universals to get one of my C628s up and running.
I replaced the stock Atlas male universal on the motor shaft with one of the older universals and replaced one end of the ends of the stock drive shaft with another of the older universal. Below are some pics of the process.
This is a pic of the original drive shaft and the modified shaft. I removed one of the female ends of the stock shaft precisely where it meets the shaft.
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The older universal slides onto the shaft with very little if any reaming required. At this point, I did not permanently attach the universal so I could adjust it later. The other older universal got put onto the driveshaft of the motor. It can go on all the way as the fingers are plenty long enough. It fits with friction, but not tight enough for me so I roughed up the shaft a bit and the inside of the universal and glued it on with CA. I would probably use different glue, but that is what I had. Because the universal can slide all the way onto the shaft, the back of the universal can actually be glued to the inside face of the flywheel for just that much more security.
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I reassembled the drive and adjusted the universal on the shaft for proper fit just like you would do on any other loco. The cool thing about fixing it in place is not glue is required. Simply use a hot Exacto knife for a tiny weld. This means you could re-use a cracked universal if need be.
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This loco also had an issue with noise long before any other issues so I looked into that since the fix above didn't help it. When reassembled, noticed a lot of slop I the motor in that it could move side to side quite a bit (by 1/160 standards) and could actually sit slightly diagonally. The bearing blocks were loose to which I noticed when I was playing with the motor. I fixed this by bending the tabs on the bearing block holders on the other side of the chassis. For the motor I put double-sided carpet tape (with the backing still on) on each end of the motor and on both sides of the motor. Why carpet tape? It was there and actually was the right thickness with the backing compared to electrical tape. The tape acted as spacers to keep the motor in place. It worked with a noticeable reduction in noise due not only to the alignment of the motor, but I think the tape added a little insulation between the motor and the bodyshell.
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The loco runs flawlessly and is much quieter (equal or better than other locos that I have).
