Repairing my old Bachmann HO scale Diesel

Old Bachmann locomotives can sometimes develop a clicking sound. I had two diesels with this problem and thought the sound was caused by the motors. Instead I learned that the sound originates in the plastic gears in the power truck. In this video I borrow parts from one of my Bachmann diesels to repair another. I'm far from an expert, so this just documents my experience making this repair for the first time.