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enter image description hereI have an older Trek Mtn bike with Shimano components. Just today the pedal started spinning without turning the wheel. I can pedal forward and backwards and occasionally it will start turning the wheel. The bike has thousands of miles on it. I am guessing the freewheel is worn out. Is this something that can be replaced easily. I have a tool to remove the cassette and have taken that off but am not sure how to proceed.

Thanks in advance, Paul

Paul
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  • The pawls in the free-wheel are either worn out or have become stuck in congealed grease.It needs to be serviced or replaced. There are plenty of videos on YouTube or on the Park Tools website that will tell you how to proceed. A replacement rear wheel is an alternative. – Carel Jan 24 '18 at 09:28
  • Are you absolutely positive its a cassette on a freehub? When you removed the cassette. was it just a pile of cogs that slid off after the lockring was removed, or or twas there a threaded bit for putting all the cogs onto the wheel at once? If its a freewheel then you simply buy a new one, and a new chain. – Criggie Jan 24 '18 at 10:39
  • If its a freewheel, all you need to do is buy a new freewheel and chain with same number of speeds and acceptable largest/smallest teeth and thread it on (after greasing threads). Note that cassettes are different (the freewheeling mechanism is in the hub, not in the cogs, and this is more complicated; you'll end up opening up the hub in this case). – Batman Jan 24 '18 at 12:26
  • I added a picture of the wheel. I would still like to know if there is a way to take apart this freewheel if I have a problem again. – Paul Feb 21 '18 at 12:10

2 Answers2

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While freehubs on modern high-end hubs tend to be easily serviced and can be detached for inspection with regular tools, I found that at least lower end Shimano parts are more troublesome in that regard.

For example, to remove a freehub from my Shimano Deore XT hub required a specialized Shimano tool which turned out to be an allen key of either 12 mm or 12.7 mm size, do not remember exactly. This is not something everyone has at home. Different hubs may need other exotic tools.

Once you manage to remove the hub body, you will need to make sure that all ratcheting pawls and their springs are not blocked by dirt. Be careful as these little springs can jump and fly away in an unknown direction quite easily.

If it is the normal wear that made things malfunction, then you should look if a replacement freehub can be bought separately. Sometimes it is the case, sometimes your only option would be to buy a complete identical rear hub and transplant the freehub from it. Or, as long as you have a whole new hub on your hands, replace it altogether. Any way, knowing the hub's model number is essential.

For example, here's an exploded view of FH-RM30.

shinano hub

The body fixing bolt part 13 is clearly detachable. It is only a question what size of a hex key is needed.

Here's a view on how it is done:

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Grigory Rechistov
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Sometimes simply flooding the freehub's body with solvent is enough to get it moving properly again.

  • Remove the wheel from the bike, ideally remove the cassette and put aside.
  • Lay the wheel over an old empty ice cream container and use a disposable medicine syringe to squirt the solvent of your choice in an at the freehub.
  • Work it back and forth with your hand

Suitable solvents/degreaser would be a citrus-based product, with petrol/diesel much further down the list. You need something that will dissolve the congealed grease and allow the springs to push the pawls back out.

Generally freehub bodies are difficult to open, but that may be your next plan if a simple flush doesn't help.

Once its running right again, remember to dry and then re-lube it a day later. Ideally you want grease in there, but I've used white lithium spray and washed that in with small sprays of CRC.

If the pawls have all broken then the wheel would never drive forward, so having it working sporadically is good news.

Criggie
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    I tried flooding it with solvent and now it seems to be free! – Paul Feb 21 '18 at 11:59
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    @paul great work - now remember that's a temporary fix and it may go bad again. Ideally you'd get all the old grease out then let it dry and finally re-lubricate. But this quick fix might work for ages, so YMMV. – Criggie Feb 21 '18 at 19:10