I need help with an overhaul of the Shimano freehub that comes with the FH-HG50 hub (part no 30H 9801). How many balls go into the inner and the outer race? What size should they have?
I have already disassembled the freehub and counted 48 ball bearings in total. They fell out of both races simultaneously so I cannot say how many were in either race. Some look larger than others and I am unsure what their nominal size should be.
Edit: After servicing the freehub, I can confirm the correct size and number of ball bearings is 25 1/8“ ball bearings for each race, ie 50 in total.
Since Shimano freehub bodies are not officially meant to be opened and serviced, there is no exploded views nor procedures in dealer's manuals available on the manufacturer's technical documentation website to confirm the size and the number of ball bearings.
Still, a few Internet users demonstrated that opening an Hyperglide freehub body such as yours is doable and they reported that there were 50 ball bearings (25 on each side) of size 1/8" on their particular model. I suppose 48 balls as you counted is also possible since it is very close to 50. The difference in size you seem to notice might be due to manufacturing tolerance. I suggest measuring their diameter with an electronic caliper if you have access to one.
This older model freehub body can be overhauled. The bearing size is 1/8" and a 25 count for both the inner and outer races (50 1/8" balls total). Often times, extreme wear of a loose ball bearing system can yield what appear to be differing sized ball-bearings. They started out life as the same diameter, but uneven wear, brinelling of the races and dirt ingress create a situation where there is uneven load so wear at any one ball can be much different than for another. I've seen bearing balls come out where the outer layers were peeling away like an onion. Other times I've seen balls that have fractured and the larger piece became rounded (albeit imperfectly) again from wear as the bearing remained in service.
A popular YouTube bike mechanic, RJ the Bike Guy, has a video discussing the overhaul of a Shimano freehub body that I link to here. It should be helpful to get you through the process.