pinion head thickness

This was along the lines of what I was trying to say in a previous post. Please review the attached diagram from the Ford service manual. Note that the special tool allows for an accurate measurement of a KNOWN FIXED distance between the pinion bearing and the axle tube lines.

The actual thickness of the pinion head is not used.

The Ford special tool improves the outcome because it is able to correctly preload the pinion bearing and the carrier housing.

If we assume that the axle tube alignment hasn't changed since the car was built and the original set up was good, the only thing that can change the pinion shim needed are the pinion bearings themselves.

This is why more often than not, the original pinion shim works. Now things like different preload, how far the pinion races have been installed into the diff housing, and differences in manf can affect the pinion shim measurement.

I will be quite and let others chime in but I don't see how the MHD method can give the correct results unless the difference of pinion head thickness is taken into account. Further, this method assumes that the new pinion races/bearing are exactly the same (which is not always true).

The pattern check never fails. Set it up with the old shim and go from there.