It is? Where is this hex screw located. All is see on my '86 740 is some sort of ring that the sensor is mounted in and it is all grunged up, and is in so tight that you couldn't get it out with dynamite. I've even tried it at the junkyard after removing the whole diff cover, and no luck. so, if this hidden screw is the culprit where is it?? P.S Import: a prelimiary check would be to check the wires as they tend to break. Then I believe that an ohm meter at the two sensor terminals should read appx 3000 ohms if the sender is good. A misadjusted Vane clearance could cause an intermittant signal or 'jumping' if the sender is positioned too far away for the Vane. Had my brick for almost year now, and never had a speedometer.
Just can't get the damn sender out. My take is to get a whole diff cover w/good sender at the junkyard and swap the whole cover over and hope it is in the correct
position in relationship to the Vane to function properly. Just am not looking forward to a day bathing in stinky old gear oil. But a new diff cover and sensor will run you about a hundred and a half, as opposed to a five dollar junkyard alternative that should work fine. Now, how to get the damn thing out!!!!!!!!!!!!!!

740man '86 740