There seems to be a few places that still sell the SG-500, like this ad from Taiwan:

NEW Shimano Alfine SG S500 8 Speed 32H Internal HUB Without Small Parts KIT | eBay

I can't help with your actual question!

Tim

 

The internal assembly part number (Y-37N 98010) is the same between the 500/501 hub. The 505 internals are not compatible, they only work with the Di2 model hubshell.

If you haven't dissembled the planetary from the axle already, you should do so. It is likely that a selector or drive pawl has broken. They are not individually replaceable, but the planetary unit is, as long as you can find it.

 

Is this the assy you mean? Part number is Y-37N 98020 though.

New Shimano Alfine SG S501 Axle Unit with Right Hand Hub Cone | eBay

I think what is broken on mine is the pawl mechanism on the drive side end. At least that's what's making the clicking freehub sound.

I ended up ordering a complete 501 so I could just swap the internals as one piece. I read something somewhere that the shells of the 500-B and 501 are the same.

If that axle unit is interchangeable, I may get that too and see if I can save the old drive unit, keep it as a backup. I pulled it completely apart, planetary off and all that, didn't see any damage to any teeth or anything, so it probably is just in the central axle/selector unit.

 

I meant the whole cartridge (axle+planetary), but if you narrowed down the issue to the axle selector, then either would work.

The tiniest bits of metal can cause a pawl to not release properly. I would dunk the whole thing in a parts washer and agitate it. Broken pawl springs are also very difficult to spot, at times. The good thing about a broken part is that you can't make non-functional worse.

If you haven't been to the hubstripping wordpress yet, you should.

 

Okay, so I got a new 501 hub, swapped the internals, smooth as butter.

I was feeling the grease on the failed 500 was looking a little sparse, or dry, or crusty, so I gave the new 501 an ATF bath before installing. Hopefully that will keep things a little smoother this time around.

 

I'm sure you've figured this by now, but those hubs need to be stripped down at least to the planetaries to grease them properly (all the meshing gears get greased).

You will have to do it eventually if you own one for any period of time, might as well practice on the dead one.

 

yeah, I'm planning to get on a regular maintenance schedule, but to some extent I was just waiting to see how long I could go without touching it. Hadn't even opened it up to look at it since new.

I ordered a new axle/pawl assy for the old 500, so if I'm able to fix it, I'll have a spare on hand.