Just wondering if its safe to "hose down" my freewheel* rear derailer with degreaser. I have the freewheel off the bike right now while I'm (hopefully ) overhauling the hub and I thought this would be a good time to scrub down the freewheel in the sink and maybe take the bike outside and scrub up the derailer with some degreaser now while the chain and wheel is outta the way. And do a good bike cleaning.

So yea, Do I need to worry about the degreaser getting inside the mechanism's in the derailer or freewheel?

Soak the derailer all you want. Just lube up the pivots with your lube of choice after all is said and done. As for the freewheel, I dont know for sure but I would personally blast it a few times with some simple green and scrub it with an old tooth brush and rinse it. Not much else you can do to clean it. Just dont blast it with a power washer or anything of the sort and all will be fine.

First, there are "degreasers" and then there are "DEGREASERS". Mild degreasers like Simple Green are o.k. to spray on and scrub or wash off. But strong degreasers (like automotive engine cleaners) can damage components and should be avoided. Even Simple Green can take the finish off aluminum parts if soaked or sprayed and left on for too long.

Second, do NOT soak the free hub in anything. That's overkill. The internal springs and pawls are lubricated with a light oil, which would be likely adversely affected by soaking in a degreaser. The rubber seals could be damaged as well.

Third, soaking your derailleur in degreaser is overkill, too. There are bearings in the pulleys that would have to be dis-assembled and re-greased as a result. A small brush (like an old toothbrush, or a grout brush, or Parktool's drive-train brush) are all that's needed to clean the parts you want to clean.

Other than soak-cleaning a chain or cassette, there is little reason to soak-clean any other parts, including the ones you mentioned.

Bob

I prefer to clean my freewheel/cassette on the hub. It's easier to spin the wheel and pull the edge of a rag through. A little degreaser helps. +1 on NOT soaking the freewheel.

Is this a splined freehub with separate cogs or an old fashioned screw-on freewheel?

Old school screw on freewheel.