I had a similar problem with 3 different shays. I posted this problem twice on this meaasge booard. I finally talked to a service technician at Bachmann and he informed me that my problem was not isolated. Apparently a bad batch of gears on some shay's trucks. He sent me a replacement pair of trucks, and now the shay runs fine. I believe that someone suggested that a gear might be cracked and sure enough one of the gears on a truck that was replaced had a large crack in it.