I've got an Alfine 8 which I've had for ~ 3 years on my mountain bike. I'm running a 32T chainring and a 24T sprocket, so quite a bit "out of spec". Since about 2 years ago, I've been running the hub with auto trans fluid instead of the shimano white grease. I've taken it apart 3 times now, and have only noticed a few filings each time.
Last ride was quite a wet and muddy one, lots of deep puddles. It's possible that some moisture made its way past the seals and into the juicy bits of the hub. I hosed down the bike and neglected to dry it (not terribly unusual). A few days later, I noticed some surface rust on the chain and some serious crunchiness while freewheeling. I lubed up the chain and shifted through all the gears, and the crunchiness decreased (but didn't totally disappear). I'm pretty sure the notchiness/crunchiness was coming from the hub, rather than the chain, though.
Anyway, I took the hub apart yesterday, and was greeted with a fine mixture of ATF and iron filings (pretty sure they were iron -- they were attracted to my screwdriver anyway) on just about every internal surface. The bearings were in near-perfect condition, and I couldn't see any obvious signs of water, though the ATF was a bit discoloured. I took off the circlip from the main shaft and broke the hub into the two main parts to see if I could see any ground down surfaces, but it was all looking quite nice. I put on the cassette joint to see if the shifting pawls were ground down. There was a slight shininess to the top of each pawl, but there was still heaps of material to allow them to engage properly, so I don't think it was the pawls anyway.
On the non-drive-side, just outside of the small bearing (near the cone assembly, but not on the bearing race), I noticed 3 gouges, which I suspect caused the crunchiness I observed. Given that these are outside of the hub, I have no idea how they were caused.
I should mention that other than the crunchiness when freewheeling, the performance hasn't been degraded at all -- still perfect shifts, and full engagement in all gears.
So I guess my questions are:
1) Which surfaces inside the hub are the most susceptible to being ground down?
2) Can the Alfine 8 tolerate this and keep working? Is it "normal" to have a few filings?
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Thread: Alfine 8 full of filings