Some suggestions. 1) Inspect the hub of the driver that came loose -- running loose on the axle can damage the inside wall of the hole in the hub -- you might want to replace the hub as well as the axle. 2) Inspect the condition of both 3-pc drivers while you have them off the axle -- is everything snug -- rim on insulator, insulator on hub, hub on axle? Many are coming loose and/or apart. In many cases I would disassemble, clean, replace parts as needed, glue, and reassemble drivers (best done with wheel cups) even if conditions weren't really bad yet just to give them some assurance of a second (50 year?) lease on life before reinstalling. 3) Check the quartering of all three set of drivers (best done with a quartering jig) -- are they all the same? At this point in their life, with who knows how many people having "worked" on an engine by now, you never know what you might find. I found many on the same engine quartered differently. Some quartered at 87.5 degrees, others at 90 degrees (both are factory settings), and others at who knows what (probably previously "eye-ball" quartered). Note: some engines were forward-quartered (6 o'clock on the right, 9 o'clock on the left) others rearward-quartered. 4) In any case, make sure all of the drivers are quartered the same way. Uniform quartering compared to mixed quartering can make a big difference to final outcome and performance. PS I used a forward-quartering 90-degree jig.
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