Up front, the problem was as much with the locomotive’s owner as with the locomotive itself. On a practical basis, fixing a problem locomotive wasn’t as hard as much as it was time consuming. And “time” spells out as “money”, which many of the brass locomotive owners were unwilling to expend. They had just spent a substantial amount on a fine brass locomotive only to find out that they needed to spend more if they planned on running it. There was a lot of moaning and chest grabbing as I broke that small fact to them. And, more than a few picked up their choo-choo and left in a huff. Over the years, I learned to be a little more diplomatic, but facts are facts. Do you want it fixed or not?
I am eternally thankful to a modeler here in Atlanta named Arthur Hambrick, who taught me the art, such as it was. The tweaking process was relatively simple. Basically, you took the locomotive mechanism completely apart and then rebuilt it, one piece at a time. The big secret was remembering how things were put back together. As you began reassembling, you tested the movement thoroughly, each step along the way.
Eventually, you would add a new piece to the drive and discover that the mechanism now had a bind or tight spot. Knowing this, you would closely examine the parts and how they fit together. Usually, there was a small burr of metal or a slightly out of center hole and such. Once you found the problem, you could correct it and continue the assembly. With a light touch of oil on the moving parts and grease on the gears, this process would yield glass smooth movement as you pushed the mechanism along the test track. Adding the motor completed the process and the client was usually happy.
In large part, this practice works with all model railroad mechanisms, brass or otherwise, but one reality remains. If the drive design is a bad one, then no amount of tweaking is going to solve the problem. And that’s where the resale market takes over. The older brass locomotives are really valuable for their nostalgia value. And as such, a lot of them deserve to be up on a shelf looking pretty.
There’s a nice overview of quality brass locomotives, here.