Unless I am mistaken both the Rangerover and Stage 1, but not the 90/110/Defender, have a CV (double cross and bearing) joint at the TC end of the front prop shaft. In theory this is required if the diff is tilted up, as the U-joints at each end are not at the same angle. (The 90/110/Defender get away with it, sort of, by setting the two joints out of phase)
Series and 101 have the pinion and TC shaft parallel, and hence the angles are equal, so that there is no vibration. I suspect that in the 101 the shafts are not actually exactly parallel, and vibration becomes obtrusive because of the relatively large angle compared to the Series ones.
In my view, tilting the diff up on the 101 would not help, although tilting it up and fitting a CV joint would. Note that the reason for the tilt on the constant four wheel drive Landrovers is to allow for the track rod, and the CV joint was necessary because of that. The 110 and its successors have a rather crude workaround simply because CV joints are expensive, and vibration is of secondary importance in utility vehicles.
John
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
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