I am repairing an older bike with a Shimano MF-Z012 cluster. with 1/8" ball bearings. Can anyone help with the number of ball bearings for both sides as the cluster has been dis-assemblied and no record kept of the number of bearing in each side
If someone is able to provide this information then that's great, but not very many people get inside freewheels to begin with and even fewer would have this data just ready to go. Shimano certainly doesn't publish it.
The right number is when adding one more would have them all touching each other without any gap.
To get there, for each side put the balls in one by one until you can tell you're almost all the way there. At that point, take the cone piece and give a gentle twist to be sure they're all seated in the ball track. Add one more and repeat. When the one you add pushes everything out of place and takes up all the gap, go back and take one away. That should be the right number. There may be some careful shuffling needed as you do this when some balls stick to the cone when you don't want them to and you have to put them back, that's normal.