Replacing roller-clutch freehub with ratchet type I live in Finland, and as such the weather right now is pretty cold.  Since I rely on my bike for shopping in a rural area, the frequent and complete loss of drive I now suffer at below-freezing temperatures is intolerable.  The local bike shop has looked at it twice now, and utterly failed to fix the problem; I don't think they've tried very hard.  When kept in a warm place overnight, it works fine, but as little as a quarter of an hour outside is often enough to make it fail again.

My own research so far indicates that I have a roller-clutch freehub (ie. it doesn't tick when coasting), which is in general more prone to failure than the ratchet type.  Most of the mechanical fittings on the bike appear to be from basic Shimano ranges; it was an ex-rental.  The model number on the hub body is FH-RM30, and the gearing seems to be an Alivio 8-speed at the rear, and a Nexave 3-speed at the front.

I'm keen to replace the freehub with a ratchet unit for reliability and longevity.  However, I'm reading suggestions that the two tend to use incompatible interfaces to neighbouring components.

My question is: how much do I need to replace?
At the absolute minimum you should be able to replace just the freehub body. Some Googling should turn up some compatible options.

The plot thickens, this hub seems to use a different freehub style to most other Shimanos. This would work with the majority of clickity hubs, but Sheldon says the silent ones are different.

The freehub body is the dark grey splined part of the hub that turns.

If you remove the axel and bearings you can pop this off with a large allen key, I forget the size, 8 or 10mm.

Getting it all back together can be a pain, the freehub's easy, but the first time you set cup and cone bearings yourself will make you curse.

The next option up, is to replace the hub with one that already has the freehub you want and get someone to relace your wheel.

Then a whole new rear wheel, then a new bike.

These options go from most to least work and least to most cash.