the 2 speed is all in the clutch bell which comes off. so if you did a motor change from one car to the next, unless it is the same car, then its likely to not work. just a matter of setting up the 2 speed bell on the other motor. i take it it is for the FW 04 ? look on the Kyosho site for instructions on the car to see what you need to change to make the other motor work, then you can setup the 2 speed.
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