Atlas make lots of railroad locomotives and rolling stock in a variety of scales, and I have several of them because of their quality and they enable me to use the chassis for other builds. In particular, I use their C-628 and C-630 N Scale models as the donor chassis for my N Scale DT6-6-2000 and RT624 kits. The chassis has been revised over the years to make improvements, but one version has an issue with the driveshaft coupling to the motor failing. In this post I’ll share with you my fix.
Below are a pair of Monon C-628s; the rear one is actually a dummy using my 3D printed chassis kit.
The powered chassis is a standard design, used on many of Atlas’s N scale locos, with a central motor and flywheels.
The chassis is held together by the two screws near each end, and the fuel tank, which clips over both chassis halves.
Inside at each end is a driveshaft linking the flywheel and the worm gear, which drives the truck towers. These simply pull out.
The motor is clipped in a cradle which in turn is clipped into the chassis.
With the motor removed you can see inside the flywheel; there’s a plastic universal joint, and it’s cracked.
The universal joint is press-fitted over the axel and uses the friction to spin it with the flywheel. Even when cracked it’ll spin so the loco will probably run okay on its own. But as the load is increased, such as adding a train, the amount of force on the split universal is stronger than the friction, and the axel just spins. So if your loco seems to run okay, but won’t pull very much, this is most likely why.
The universal joint is a plastic tube with two pegs which fit into the driveshaft. The hole in the tube will be smaller than the axel to create the required tight fit but the constant pressure on this particular material causes it to crack.
Replacement universal joints are available from Atlas, but these have been known to fail as well. So I’ve 3D modeled the part and printed it in Shapeways Smooth Fine Detail plastic because it’s both accurate and also hard-wearing
The new part is a direct replacement for the original.
If the old universal is cracked it should simply pull off leaving a clear axel inside the flywheel.
I fitted the new universal by placing it with a pair of tweezers but not pushing it on fully, just enough to hold it in place. If it’s pushed at an angle it too may crack.
I then used a flat screwdriver, as to give even pressure, to push it on fully so the universal is all the way to the back of the flywheel.
And that’s it. The loco is ready to be reassembled.
These are now available in packs of two and four using the links below:
This universal is used in many of Atlas’ diesel locomotives and will fit all.
I’m juggling an HO project as well as testing recent 3D printed replacement parts, but my focus is on returning to work on customer’s layouts where possible, so who knows what I’ll be sharing next week!