Mercury V6 lower unit driveshaft up & down play

[rocketracer]

hello, new to mercs lower unit maintenance, so bear with me. just removed unit for pump inspection and noticed driveshaft (vertical shaft) has about a 3/8 up & down movement. when down it has a slight ratchet as it spins, when pulled up it is very smooth, is this normal? motor working fine with no noises before removal of unit. Thanks

[Onetime]

Normal for lower units pre Sportmaster. The design theory was that as soon as the engine fired up spinning the driveshaft it would push the driveshaft up to seat against the tapered roller bearing.
Not until Sportmaster lower units with the double opposed tapered roller bearings did this change. Pretty sure non race production lower units still use the same single tapered roller bearing set up.

[flabum1017]

All mercs (other than versions with double opposed bearing) without the pre-load pin are designed to make the pinion ride up the gears when running and put upward pressure on the drive shaft.
The shimming procedure requires a tool to put upward pressure on the drive shaft to set the gear backlash. There is no bearing to limit the downward travel, the ratcheting you feel in the down position is actually the pinion nut scrubbing the clutch dog. Race lowers with the double opposed bearings will have no vertical travel........