Broken freehub

nbuuifx
nbuuifx Posts: 302
in MTB workshop & tech
My son's bike suddenly has a broken freehub. It has never been a problem, then we went to go for a bike ride the other day and his legs just spun, so that ended that idea!

It happily spins in either direction. I've replaced one before (albeit on an adult bike) and with that one it was cheaper to buy a complete replacement hub and take the free hub off and put that onto the old wheel and hub.

I've started to dismantle this one, but got stuck at the actual point of taking the freehub off. With the last one I inserted a 10mm Allen key (I can confirm it was 10mm as the old broken freehub is still in my toolbox - no idea why!) - Anyway, with this one, the 10mm allen key just floats about inside. I presume it is an allen key again but larger - any ideas what sizes are used?

The bike is a Dawes Academy 24". It has Shimano 8 speed gears. From a spec sheet that I read, it says it has a Shimano Freehub but I couldn't guarantee that - I couldn't see any markings on the hub.

So in summary...

What sizes of allen key are commonly used?
Any ideas what replacement hub I need to buy?
Are they interchangeable between 6/7/8 speed?

Thanks

Comments

  • mully79
    mully79 Posts: 904
    They are usually 11 mm.
    If you have a 3/8 socket set try using the square end of the extension.
  • nbuuifx
    nbuuifx Posts: 302
    mully79 said:

    They are usually 11 mm.
    If you have a 3/8 socket set try using the square end of the extension.

    Thanks I'll give it a go. I'd be surprised if it was 11mm as 10mm seemed quite sloppy.
  • nbuuifx
    nbuuifx Posts: 302
    mully79 said:

    They are usually 11 mm.
    If you have a 3/8 socket set try using the square end of the extension.

    The square end of a 3/8 extension bar is also too small.
  • veronese68
    veronese68 Posts: 27,329
    Try using bolt heads to see what fits, assuming you have some old bolts kicking about.
    Kinesis Pro6
    Marin Nail Trail
    Cotic Solaris
  • masjer
    masjer Posts: 2,567
    The pawls inside the freehub might have seized/rusted. If it's a Shimano type freehub, (for a quick fix) you could try flushing out the freehub in situ with wd40 or similar-then re-lube with oil.
  • nbuuifx
    nbuuifx Posts: 302
    veronese68 said:

    Try using bolt heads to see what fits, assuming you have some old bolts kicking about.

    Good idea...

    I tried this, it turned out that I couldn't fit the head through the inner race from the bearing though. So I drifted the non drive side race out. I could then see that it wasn't hex shaped at all.

    It isn't a pefect fit, but I found a Torx T60 fits fairly securely. I put a bit of pressure on but it feels like it needs a fair bit of pressure to remove. Before I do this, when inserting the tool from the non drive side which way should I be turning it?
  • steve_sordy
    steve_sordy Posts: 2,446
    I've had a freehub that failed like that, not a Shimano one though, but e13. It was the springs holding the pawls in contact with the ratchet. There were three pawls (and springs). Once I had seen what the problem was I remember having noticed that the crank travel before drive had been erratic recently; sometimes fine, sometimes a bit of extra travel before drive.
    So, one one spring had rusted through, then the next. But it was only when the third one failed that the drive failed completely. The seals on the hub had failed, it was a faulty design and the hub failed every 700 miles or so. Warranty claim every time.
  • nbuuifx
    nbuuifx Posts: 302
    Well I figured it would probably be anti-clockwise from the freehub side so I tried clockwise from the non drive side. It wouldn't budge, so I used an extension tube over the ratchet to give me extra leverage. It felt like it turned about an 8th of a turn (could have been slipping I guess) but then wouldn't shift any more - however the freehub now appears to be working fine.

    Is this likely to last?! I tempted to put it back on and get my son to give it a try. I'll be a bit nervous about going on a long ride though.
  • nbuuifx
    nbuuifx Posts: 302
    masjer said:

    The pawls inside the freehub might have seized/rusted. If it's a Shimano type freehub, (for a quick fix) you could try flushing out the freehub in situ with wd40 or similar-then re-lube with oil.

    As above it has started working now - which may link with what you suggested. Where do you flush it from? It all seems sealed - do you just get some wd40 round the ends and hope it penetrates in? I might try this in addition to help!

  • masjer
    masjer Posts: 2,567
    It depends on the freehub design. If there's an outer bearing in the freehub blocking access to the internals (and you can't remove it) you could try putting a few drops of oil (3in1,thin chain lube or even engine oil) through the centre hole in the bearing, where the axle goes.
  • nbuuifx
    nbuuifx Posts: 302
    I decided not to do the WD40, as I thought it might wash out any grease in the freehub and as I couldn't get to replace it, it might make things worse.

    I've regreased the bearings and reassembled everything and put it back on the bike. All seems to work well - will get my son to test it out tomorrow if it doesn't snow.

    Thanks for the help - I seem to have fixed it through luck rather any real fix but hopefully it will keep going for a bit! - I might keep an eye out for a second hand pair of wheels as spares.
  • thecycleclinic
    thecycleclinic Posts: 395
    Once a freehub starts to fail it will faiI again of you manage to get it going. The bearings in the freehub are probably toast any way. The inside is just like a old freewheel. Whether you can buy a new freehub is another matter.
    www.thecycleclinic.co.uk
  • steve_sordy
    steve_sordy Posts: 2,446
    You probably just shifted one of the pawls so that it now functions. But as @thecycleclinic said, once it starts to fail it will fail again. Only next time you might be a long walk from home. I would not trust it.
  • donslow
    donslow Posts: 69
    Not a constructive post to say the least but I had the Same thing happen to me just a week or so ago, happily pedalling along then boom! Legs spinning, cassette spinning but nothing else followed by a near 3 mile walk home with shoes filled with frozen water and -2 temperatures, who say mountain biking isn’t fun?!

    Took the wheel off and my cassette with freehub still attached just pulled off

    Still trying to work out EXACTLY what has gone so wrong but after cleaning up the back of the cassette the pawls are all missing and the springs are done for

    Can’t work out how to post pictures here otherwise I’d share what I found

    Good job I had a whole new hub (scratching an upgrade itch) in the post at the time

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