Explaining a 'shot' cassette body...

Brad Spachman said:

Hi all...

Medium-time lurker...first-time poster:

I had my Specialized Sequoia in my LBS this week to take care of a few
problems (busted spoke, tune-up, etc.) I picked it up today and the
shop guys had put a note on my bill saying that 'your hub was fine'
but that I had a 'shot cassette body' and that I should have them
order a new one, etc. etc.

However, they also said I could continue riding on it until it 'blew
up'. I had to run out of the shop to get back to work, so I didn't get
to spend enough time hashing over what exactly is broken.

Now, I know it isn't going to actually explode (I hope), but can
anyone explain to me what the cassette body is, what it means when
it's shot, and what kind of failure mode(s) I might reasonable expect?

P.S. Shimano 9-speed: 105 series throughout....

P.P.S. I investigated Sheldon's site and found this page
(http://sheldonbrown.com/k7.html), but the terminology didn't seem to
match up.

Thanks,
brad

Since the introduction of cassette systems, the cassette contains the
actual freewheel mechanism. The cassette sticks out of the rear wheel
and the cogs slide over it. On older systems the cogs and the freewheel
mechanism are parts of the same unit. the likeliest failure is that you
lose the ability to freewheel i.e. the cranks move with the rear wheel.
alternately, I suppose the freewheel could stop engaging the rear wheel.
As long as the bike is working now, I wouldn't worry about it. (assuming
you're not planning any long rides in the middle of nowhere)

Derek Hodges said:

Since the introduction of cassette systems, the cassette contains the
actual freewheel mechanism.

I think your terminology is a little off. The cassette is just the assembly
of cogs and spacers that are installed onto the freehub. The freehub body
(which is part of the freehub, not the cassette) is where the ratchet
mechanism that allows freewheeling resides.

See:
http://www.sheldonbrown.com/k7.html#advantages

It's possible that one of the pawls in the freehub body isn't engaging, or
some other problem. I'd ask the LBS for more details before replacing it.

Quoted message said:

The cassette sticks out of the rear wheel and the cogs slide over it.

The freehub body sticks out, and the cassette slides over it.

Art Harris

Brad Spachman said:

I had my Specialized Sequoia in my LBS this week to take care of a few
problems (busted spoke, tune-up, etc.) I picked it up today and the
shop guys had put a note on my bill saying that 'your hub was fine'
but that I had a 'shot cassette body' and that I should have them
order a new one, etc. etc.

The terms are confusing you, I think. There is a cassette (the cogs and
spacers on which your chain rides), there is the hub (the center of the
wheel that receives the spokes), and there is a freehub body (the
ratcheting mechanism that goes between the two). To make things a bit
more confusing, the term freehub usually refers to a combination of the
hub and the freehub body. Your shop's term "cassette body" is an odd
term since it contains parts of two of the names.

After you get those terms straight, I think you can go back to Sheldon's
site and understand it.

Quoted message said:

However, they also said I could continue riding on it until it 'blew
up'.

Quoted message said:

Now, I know it isn't going to actually explode (I hope), but can
anyone explain to me what the cassette body is, what it means when
it's shot, and what kind of failure mode(s) I might reasonable expect?

If they meant cassette, I don't think they would have recommended that
you ride until it "blew up." They probably would have recommended a new
cassette and chain pronto.

So I'm pretty sure they mean that the freehub body (the ratcheting or
freewheeling mechanism) is worn out. If that fails while riding, you
will notice it by the slipping action. You might get an occasional slip
that feels like the chain has jumped off the gears momentarily. Or it
might fail suddenly, so that one moment you're pedaling normally, the
next moment you'll be pedalling with no load (freewheeling, like you do
when you pedal backwards).

The worst part is that the freehub will probably fail when you're
putting a high load on it. For example, standing to pedal up a hill,
starting off from a stoplight, .... As you might imagine, that's not a
good place to suddenly freewheel. The odds are that you'll be scared
when it happens, since you'll momentarily lose control. It might even
hurt. I'd personally recommend replacing a freehub that's about to fail.

Now for the good news. I don't know how the shop can tell a freehub is
about to fail unless they took the whole thing apart. I'll bet $100 they
didn't take it apart. Take a look at the procedure at
http://easywebshop.co.uk/bristolmtb/mtb_diy_freehub_shimano.htm
and I'm sure you'll understand why I say that. Most shops won't rebuild
freehubs, they'll just replace them.

You might first call the shop and make sure you have the terms straight.
See if cassette body = freewheel body. If so, I'd suggest spinning the
freehub with your bare hands (wheel off the bike), and if you can't find
anything unusual, ask the shop how they know the freehub is shot. If you
find something unusual or if they make a reasonable case for their
theory, replace the freehub. The part is probably about $20, it
shouldn't take them much time to do the job, and you'll have peace of mind.

--
Dave
dvt at psu dot edu

In article <[email hidden]>,

dvt said:

Brad Spachman said:

I had my Specialized Sequoia in my LBS this week to take care of a few
problems (busted spoke, tune-up, etc.) I picked it up today and the
shop guys had put a note on my bill saying that 'your hub was fine'
but that I had a 'shot cassette body' and that I should have them
order a new one, etc. etc.

Quoted message said:

Now for the good news. I don't know how the shop can tell a freehub is
about to fail unless they took the whole thing apart. I'll bet $100 they
didn't take it apart. Take a look at the procedure at
http://easywebshop.co.uk/bristolmtb/mtb_diy_freehub_shimano.htm
and I'm sure you'll understand why I say that. Most shops won't rebuild
freehubs, they'll just replace them.

Thanks for the link! I can definitely see why it's more of a
replaceable part than one anybody wants to service. Looks like prices
online for shimano hub/freehub assemblies range from $20-$50, and that
would save a lot of time instead of mucking about with all those
bearings & pawls.

Quoted message said:

You might first call the shop and make sure you have the terms straight.
See if cassette body = freewheel body. If so, I'd suggest spinning the
freehub with your bare hands (wheel off the bike), and if you can't find
anything unusual, ask the shop how they know the freehub is shot. If you
find something unusual or if they make a reasonable case for their
theory, replace the freehub. The part is probably about $20, it
shouldn't take them much time to do the job, and you'll have peace of mind.

Thank you for your clear explanations. They all fell in line with what
I expected. I wish I had had more time when picking up my bike to quiz
the shop guys, but I'll try to make it up there this week and see if
they can clarify themselves for me.

In the meanwhile, I'll just keep on pedaling!

Best,
brad

Brad Spachman said:

Now, I know it isn't going to actually explode (I hope), but can
anyone explain to me what the cassette body is, what it means when
it's shot, and what kind of failure mode(s) I might reasonable expect?

Presumably, they're talking about the part of the freehub on which the
cassette is mounted, and I would have to guess that they're stating
that it's worn in some manner. Wear in this part tends to happen
slowly. There are several possibilities, if there's actually wear
present. Before I'd spend any money, though, I'd want to get more
information. If the assessment is based on wobble in the casstte
which is only present when freewheeling, I would ignore the
recommendation and find a different shop for future work.
--
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