Many years ago, when they first came out, I bought a Bachmann 2 Truck Shay with every intention of making my grand garden route. Life got in the way and during some leaner times it was sold. Last Xmas, my two grown boys rekindled the dream when they bought me a NOS Shay that had never been out of the box (included VHS instructional tape.) I set up an oval of track and proceeded to turn into a child. On the third outing with almost no weight in tow, it broke the final drive gear on the rear axle (which I now know they are prone to do.) Since parts are hens teeth and I really didn't want to pony up multiple $ hundred for new trucks, I decided to see if I could fix it. A friend who had been into R/C cars noticed how much that gear looked like a pinion gear so the search was on. We came up with a steel gear with the right diameter, pitch, and number of teeth to match the BS plastic one that broke except the axle hole was 5mm and the Shay axle is 6mm. Getting the axle out was quite the adventure with the pickups and all (thanks to those that helped here). Found a 6mm bit and drilled the gear out on the drill press. Pressed off the bearing and chucked the axle up in the DP so I could file down the knurling for the old gear. Made a flat spot with my Dremel to accommodate the set screw of the new gear and then pressed it all back together. With some adjustment and tuning I now have a fully functional Shay once again and I will be damned if that gear will ever break again. Did the second axle in that truck and ordered 2 more gears to do the front truck. If anyone wants pics and details I can provide em.