2000 forman es 450
 

Have anybody had shifting problems with this type of atv? It shifts ok when it's cold but drive it for an hour it becomes impossible to shift.

The 2000 model 450 didn't have the "fault code" system of later 450s so you are working blind if a fault occurs. My guess would be either the angle sensor or the shift motor. Although you can theoretically test the sensor, we go for substitution, fit a new one and if the fault is still on, it wasn't the sensor. However it costs nothing but time to strip and check the shift motor for worn brushes or an oiled up comutator etc. Be warned though, the motor is an absolute swine to get back together.

Thanks, I'll look in to it.

have you tried shifting with the foot shift when you are having problems with the electric shiftÉ, just to help rule out possible causes...

The mechanical shifter works fine.