Earl Grey

I pulled the freehub body off a new Shimano hub (FH-3500), mostly out of curiosity while I was applying marine grease to the main bearings.

The back (inboard) side of the freehub body has a small rubber seal protecting the inboard set of freehub ball bearings. There's no other seal around the edge of the freehub body where it sits slightly recessed in the hub (and rotates relative to the hub, while coasting).

Seems like this hairline between the hub 'proper' and the freehub body would be a very easy place for water to get in behind the freehub body. Is there any reason not to slather the back of the freehub body in grease before reinstalling it in the hub?

I haven't had one of these apart before. The freehub internals seem much better protected on the outboard end (water has to get past the main axle's drive-side seal, the main axle cup / cone and a relatively large amount of grease). The freehub internals (I dismantled that too... ) have only a very light oil from the factory that isn't going to slow up water ingress if any gets past that inboard rubber seal.

bikeman715

you can add grease to the freehub or behind it if you like . most here will tell you not to because it can interfere with the paws of the freehub . the rubber seal you referring to , does a great job of keeping water and dirt out of the freehub .

davidad

You are overthinking this. The hub seals won't keep water out if you submerge the hub. They are basically dust seals. I haven't ever had a problem with water in my shimano hubs and a couple of them have well over 40k miles on them.

Earl Grey

Interesting, thanks both. So it sounds like a non-problem in real life, grease or not.

Definitely not adding grease to the freehub body internals themselves, by the way.

bikeman715

Sound like a plan . as you said it a non problem in the real world .

Andrew R Stewart 

I usually grease mating surfaces unless I know that I shouldn't. So the lobed FH body/shell contact gets a thin film of grease in my servicings. Andy.

Earl Grey

Thanks Andy - yes, that part I would give a smear on the same principle. I was pondering running a heavier bead around the edge of the recess in the shell in which the FH body sits (i.e. behind the hairline gap between freehub body and shell). It sounds like people feel that's of little value / overkill.