Disconnect the linkage and try to shift the lever at the control valve by hand. You may have sheared the roll pin that passes through the linkage and the actuator shaft that goes into the control valve. This was very common on those machines, you may even find the whole worn out and loose on the shaft. If you do, simply drill it out and the holes in the link to match the next size up roll pin. I did this repair many times and if you have a long enough drill bit you dont even have to remove the control valve.