The joy of playing with initially well running locomotives does not always remain undimmed. In some locomotives in particular, damage to the gearbox occurs over the years, even though the hobbyist has handled his vehicles with care and has even not used them for a long time. Who hasn't experienced this? At some point, you've bought a locomotive and, of course, let it run. Everything's fine, it runs perfectly and beautifully, just as it's almost typical for American machines and as is generally the case for locomotives in this category. In short, you are satisfied with the purchase. After a year or two, the moment comes when you want to use it again. But now comes the scary moment: you put it on the tracks and are shocked by the terrible driving behavior: the locomotive no longer runs as smoothly as it did at the beginning, but instead it hobbles, makes a terrible noise and has almost no tractive power anymore. The hobbyist will initially suspect power pickup problems, clean the locomotive and rail, but there is no success. Lack of lubrication? But after clipping off the floor cover on the bogies, you notice that everything there is floating in grease, so everything is OK? The layer of fat makes it almost impossible to identify the origin of the problem at first, because it's in the gears! One or more of them have cracks that are the cause of the poor driving behavior. Tooth by tooth Once you have found the basic fault, you can then easily start to fix it. But knowing the cause is also quite interesting. The transmission pinions of the drive axles were made of plastic at one time and this has the property of becoming brittle after a while if it is not used regularly. Partly this is due to the plasticizer and/or the material. If you want to use the locomotive again after a long period, the plastic gear(s) tend to burst. This longitudinal crack affects the distance between the teeth; if there is a gap, they can no longer mesh well or slip through .The defective spot sometimes comes together tooth to tooth and the machine hops as a result. You can also recognize the fault by a slight, dull impact. Today these pinions are made of softer Teflon and the problem of them becoming brittle due to drying no longer exists. This short description is valid for both new and used material. The solution to the problem is to replace these pinions. You can purchase it from a good American model railway dealer. There are two variants, once the pinion alone and once the entire axle. If you place the locomotive backwards in a locomotive bed, you can see a cover on the bogies (picture 1), which extends over the entire length. This must be lifted and removed very carefully with a fine slotted screwdriver. Then the axles with the plastic pinions are presented to you. You lift them very carefully out of the holder and pull the two halves of the axle apart, (picture 2), removing the gear from its counterpart. It is important to ensure that the two brass squares on the outside of the pinion do not get lost. They have the function of passing on the current from the wheels to the power strip on the side. Now that the various parts of the axle are on the table, you can replace the defective gear with the new one. Then check the track width using a gauge or on a piece of track and you can reinsert the whole thing. But be careful, inserting, it requires a bit of patience (picture 3), as the brass blocks don't always want to slide into place right away. Then you have to help with tweezers. Once the axles are back in their place, you should let a drop of oil or grease (really just a drop) run into the new pinion. Then you clip the cover plate on again very carefully. Once, new parts have been brought together with old parts, it is a good idea to let the locomotive run in both directions again for at least a quarter of an hour. Once this has been done, you can have fun again, playing with the locomotive.