The humming noise was probably the gears, which is I imagine what your mechanic thought.

If you go back to my first post, I tried there to explain that the sensor can't change the number of pulses it gets per revolution, whether it's the right one or not (and sensors don't interchange between older and newer axles, anyway).

If the axle has a tone ring that the speedo was not built for, the speedo will read wrong. One way to deal with that is to install a speedometer that IS appropriate for whatever tone ring is in there.

I think the thing to do now is to ascertain which tone ring is installed in the rebuilt axle (12,48 or 96 pulses per revolution) and which one was in the original.

Our original assumption here was that the '93 has a 48-pulse ring and that earlier rebuilt ones have a 12-pulse tone ring. That is true here, but your 60kph VICE 100kph reading leads me to believe it may not be true there.

In any case, the mechanic can fix the original axle, or he can transfer the original tone ring into the rebuilt axle (I have never torn into a differential, so I can't estmate how hard that would be. What I've read indicates that it takes special tools, time and skill to get it apart and back together properly, even if you don't replace parts)

Or you can attack the problem from the speedo end.

Or you can find someone who can built circuits to convert frequencies from what you aare getting from the sensor to what you need for the speedo.

But a different sensor will NOT help, unless perhaps the one that is in the rebuild is faulty.

Good luck
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jds