Best bet I think is to buy the replacement trucks if you can find them. I don't think that Bachmann sells the individual gears or truck parts, but only the whole replacement sets. Just curious, are you actually talking about the 38 ton Shay that did come with the upgraded trucks, or are you really referring to the 36 ton Shay that has the earlier failure prone trucks. If you really are talking about the 38 ton model, that is rather concerning that the upgraded trucks are now failing as well?!?!