Bicycle Mechanics - Free hub for old wheel hub

Hi all,

I have an older Specialized Hardrock MTB (w/a FH-RM40 rear wheel hub) on which I may need to replace the free hub. It's a 7-speed. I've figured out the Shimano part no. for the free hub (and it may or may not be available). However, there's what appears to be a newer free hub (for a FH-M290 real wheel hub) that may work, but I haven't been able to confirm or deny it. Anyone have any experience or insight with this?

Also, if I wanted to change my system to an 8-sp., any ideas on the freehub I could use? (I know there are some technical concerns with spacing and shifters that I might need to attend to).

Appreciate any input anyone can provide.


Cheers....Steph

With some exceptions, all Freehubs are generally compatible with eachother. I recently put an 8-speed Freehub on my 7-speed wheel. I have no idea what the part numbers are, but it worked fine. I needed a new right-side cone to make it work, and my LBS was able to find one and only charged me a couple bucks. IMO, this is a good time for you to get an 8-speed Freehub to run an extra speed. You might be able to use your 7-speed shifters too if you can get an extra click out of them somewhere.

Fastjake is correct, most Shimano 7 and 8/9-speed freehub bodies are interchangable on but each model may have a different cone and dustcap/seal configuration so some scrounging may be needed to match the new freehub body with the axle and hub shell.

If you substitute an 8/9-speed body on a 7-speed hub you may be able to retain the current axle. If the hub was spaced 130 mm or 135 mm already, no problem. If it was spaced 126 mm you can still use it for 130 mm dropouts with a reduced but adequate axle protrusion past each locknut. If it is to go on a 135 mm spaced frame, you will need a longer axle.

You will need to redish the wheel.

Thanks much for the info and suggestions.

I'll have to visually verify, but based on Shimano's specs, this hub came with either a 130 or 135 mm "over lock nut dimension" (A man with no watch doesn't know the time, a man with 2 watches is never sure... :(

It's good to know the interchangeability of the free hubs (Shimano has a document of sorts, but it isn't very clear what they are trying to convey with it).

A couple of other questions....the hub on the bike now is a Hyperglide-C. I thought I heard/read something somewhere about a difference in mounting requirements for the cassette/gears....possibly in going from a 7 to an 8/9 freehub. Or is that just specific to mounting on a Hyper-C as opposed to a non-C freehub?

Also, any general sense of how much play (runout?) there should be on the hub? I have a bit of play, but the shifting is still pretty solid (bike/freehub has 15K+ miles, cassette/chain less than 3K). Only a slight "hiccup" when going from 5th to 6th (but not from 7th to 6th). Maybe I shouldn't be too worried about the hub at the moment and just replace the cones (which I know is needed).

Again, appreciate the support from all.

Cheers...Steph

the hub on the bike now is a Hyperglide-C. I thought I heard/read something somewhere about a difference in mounting requirements for the cassette/gears....possibly in going from a 7 to an 8/9 freehub. Or is that just specific to mounting on a Hyper-C as opposed to a non-C freehub?

Also, any general sense of how much play (runout?) there should be on the hub? I have a bit of play, but the shifting is still pretty solid (bike/freehub has 15K+ miles, cassette/chain less than 3K). Only a slight "hiccup" when going from 5th to 6th (but not from 7th to 6th). Maybe I shouldn't be too worried about the hub at the moment and just replace the cones (which I know is needed).

The "C" means compact, which just means it allows the use of an 11 tooth sprocket. If you want to use an 11T sprocket on your new Freehub, you need a Hyperglide-C unit. See the difference: http://www.sheldonbrown.com/k7.html#hyperdrivec

All Freehubs I've worked on do have a little play, even when brand new. If yours still freewheels fine and doesn't have any other issues I wouldn't bother replacing it. Unless you want to upgrade to 8/9/10 speed.

& 7 to 8 is just adding a cog , not really an upgrade, do you want a different ratio? , get that sized sprocket offered in a different 7 speed cassette..

Shimano's K cassette for a bike tourist , like Me, is a perfect combination.

Speed is the effort put out, not the parts bought.

Again, thanks much for the advice and the pointer to Sheldon's articles (been there a few times in the not so recent past).

I already have an 11T gear on my cassette (which is a Hyper-C), and after reading a bit more and talking to some folks, I can't see any reason to move to an 8-speed version. I figured if I had to replace the freehub anyways (due to wear and tear or failure), it was something I wanted to consider.

After talking to the service tech at my LBS (Performance Bike) a bit more, I'm pretty convinced my freehub is prob'ly working just fine. Shifting is pretty consistent (as in fairly smooth and quiet, given the bike's age) except when it occasionally gets a bit temperamental going 5->6 (but not 7->6). The amount of play bothers me (but what do I know ;) but doesn't seem to be that big an issue. I know the cones need replacing so I'll do that and check bearings and axles at the same time and get back to riding ASAP.

Forks/front hub is next on my list....

Again, appreciate the input. It helped to confirm what I sort of believed at the outset.

Cheers and regards.....Steph