Broken wheels inside
Jim, there are several small plastic wheels mounted on independant shafts on one half of the wheels. The other half snaps over them. You may have 1 or 2 wheels that broke their shaft, thus loosening the tension on the other half, allowing separation. I had the same problem last year. Replacement is very expensive as the wheel comes with the motor. Assuming you have all the wheels, here is what I did and it works like a charm for less than $5 and about 1 hour of work. Unscrew the wheels from the broken shafts. Using some type of Krazy Glue, replace and glue the shafts back in their original position. Once glue is good and dry and has set properly, drill a small hole clean through, coming on the outside of the wheel half that the shafts are part of. I drilled a hole large enough for a #4 bolt. Buy some #4 brass or stainless bolts (if my memory is OK, they have to be 1") with a pan head, some lockwashers, and some hexnuts to fit the bolts. Install bolts in hole and through shaft, with pan head on outside of wheel half. Reinstall small plastic wheels, then lock in place with lock washers and hexnuts. Tighten lightly and file down excess length of bolt (that's why I used brass) to make flush with hex nut. Reinstall belt and carefully snap other wheel half back in place. I did that last July, and my ST-4000 has worked flawlessly since. Good Luck
