I have just tried to repair an '86 240 odometer with the same problem, working speedo, no odo. I disassembled it, found the trashed gear, ordered and installed said gear, but still no go. Upon further inspection I found the reason for the problem. When the P/O tried to repair it two years ago, he broke one of the fine wires that powers the little dc motor. The motor is mounted on three soldered studs on the pc board with the feed wires wrapped around the studs and then fed into the motor housing.Once you remove the screws to the circuit board, they also act as a motor hold down,turning the assembly upside down with no support is probably sufficient to break one of them. I am going to get out the 10x loupe and solder gun, remove the studs and wires and give it a shot on a repair. But it is probably going to be junk yard time Sat.