Tec talk: loose casette

[sanuk]

While in the middle of an 800 km ride last week I noticed a repetative slight knocking coming from the rear cogs - specifically two of the mid-range gears which get quite a bit of use when I'm loaded up.  Wouldn't go away and no visible evidence of anything wrong until I tried wiggling the cogs with my fingers while stationary and with the chain tensed.  What I found was that with the chain in the lower gears - the smallest cogs - I could move the entire upper cassete back and forth by about 3 cms each way.  If I put the chain up into the largest cogs I could do the same with the lower part of the cassette.  Note: this only was possible with the part of the cassette without the chain holding the tension.  When I returned from the trip - nothing bad happened except the continuing knocking - I compared with my mountain bike and I can't get that kind of movement on that cassette.  So what's going on in there?  I have no tools for dismantling the rear cassette and/or tightening it and wouldn't know how to go about it anyway.  It looks serious and fortunately I wasn't all that far from home, but if I'd been in the middle of Tibet!!!!  I can take it to my local bike mechanic but would like to hear what others might have to say. In all other respects it changes gear smoothly.  It's Shimano Deora XT and only a year and a bit old so you'd think it wouldn't just fall apart.

[staehpj1]

While in the middle of an 800 km ride last week I noticed a repetative slight knocking coming from the rear cogs - specifically two of the mid-range gears which get quite a bit of use when I'm loaded up.  Wouldn't go away and no visible evidence of anything wrong until I tried wiggling the cogs with my fingers while stationary and with the chain tensed.  What I found was that with the chain in the lower gears - the smallest cogs - I could move the entire upper cassete back and forth by about 3 cms each way.  If I put the chain up into the largest cogs I could do the same with the lower part of the cassette.  Note: this only was possible with the part of the cassette without the chain holding the tension.  When I returned from the trip - nothing bad happened except the continuing knocking - I compared with my mountain bike and I can't get that kind of movement on that cassette.  So what's going on in there?  I have no tools for dismantling the rear cassette and/or tightening it and wouldn't know how to go about it anyway.  It looks serious and fortunately I wasn't all that far from home, but if I'd been in the middle of Tibet!!!!  I can take it to my local bike mechanic but would like to hear what others might have to say. In all other respects it changes gear smoothly.  It's Shimano Deora XT and only a year and a bit old so you'd think it wouldn't just fall apart.

It sounds like the lock ring that holds the cluster on the freehub is loose to me.

The screw that holds the cluster together when you take it off usually does not attach the smallest two cogs, so it would make sense that they would move separately.   So that screw is probably OK, but if it isn't sometimes it can protrude from the cassette and damage spokes.

If it was me, I'd take the cluster off be sure the screw that holds the cluster together is tight and reassemble and tighten the lock ring.

Another possibility is that the cluster was assembled without one of the spacers.  If that were the case it would have been that way from the get go.  I think that is unlikely as it would probably have never shifted right from the start.

Edit: I carry a Unior Cassette Cracker to remove or tighten the cassette on the road.  I think it weighs less than an ounce and would allow fixing this pretty quickly.

[John Nelson]

I could move the entire upper cassete back and forth by about 3 cms each way

You must mean 3 mm, right?

The last time I had a cassette that rocked, my lockring was tight but I had installed the smallest cog incorrectly (i.e., not lined up correctly with the splines) and it prevented the cassette from coming together tightly.

[BrianW]

Most likely the lockring is loose, as others have mentioned. I've had this problem with XT cassettes on my tandem.

Has the cassette been removed and reinstalled recently? Perhaps a spacer is missing or something is not aligned well. On XT cassettes the larger cogs are all part of one carrier, and the smaller ones are individually mounted.

Tools are cheap and easy to use for removing and replacing cassettes. For home use, you'll need a lockring tool ($8-10) and a chain "whip" ($15-20). Good to have them to fix spokes, clean the cassette and the hub, etc.

[staehpj1]

Tools are cheap and easy to use for removing and replacing cassettes. For home use, you'll need a lockring tool ($8-10) and a chain "whip" ($15-20). Good to have them to fix spokes, clean the cassette and the hub, etc.

If the budget is tight it is pretty easy to make a chain whip.  You can also improvise one pretty easily with a chain and some kind of clamp or vise.

[Pat Lamb]

Agree that the cassette lock ring is probably loose.  The tool to fix it costs $5-10, plus a big adjustable wrench.  You might ask a bike shop how much they'd charge to fix it -- I'd guess free to $5, unless they're one that has a $25 minimum labor charge.  (Even then, this is so easy they might do it for free.)

Two years in a row I had this come loose, both times in the middle of the same "event" century.  Second time I was within a half mile of a SAG stop with a mechanic.  The third time I figured it out, found some loose alignment bolts in the cassette, and tightened them.  Those alignment bolts supposedly aren't necessary, but the problem hasn't recurred (yet?).

[staehpj1]

You might ask a bike shop how much they'd charge to fix it -- I'd guess free to $5, unless they're one that has a $25 minimum labor charge.  (Even then, this is so easy they might do it for free.)

If it happens during a longish tour the odds of them either doing it for free or handing you the tools to do it yourself go way up.  At least that has been my experience.

[Pat Lamb]

You might ask a bike shop how much they'd charge to fix it -- I'd guess free to $5, unless they're one that has a $25 minimum labor charge.  (Even then, this is so easy they might do it for free.)

If it happens during a longish tour the odds of them either doing it for free or handing you the tools to do it yourself go way up.  At least that has been my experience.

That's another reason to go E-W -- it's cheaper in small towns in the west, IME.    Changed out brake pads in Clark Fork, ID, for $3 and a quarter of a pack of Fig Newtons, and trued a rear wheel AND relubed Frog pedals in Missoula for $8.

[sanuk]

Thanks for the input.  Not sure if it was the cassette lock ring or what but I took it to my local French bike mechanic this morning and he fixed it in a couple of minutes.  He took the wheel off, took out the spindle/wheel locking device - sorry if I get the terminology wrong - and used a wrench on one end and a long allen key inserted on the other and tightened them up.  Seems to have solved the problem although I'm not sure what he actually did or what got tightened.  He's not given to much in the way of explanation, but is the only guy in town I come close to trusting and can sort of communicate with and fixes most of my bike problems for free ever since I bought a Trek mountain bike from him six years ago.
Next time I do a long trip in parts of the world where the only so-called mechanic you'll likely see is a village teenager with a blow torch and a big hammer I'll try to get the tools mentioned above and figure out how to use them first.

[FredHiltz]

I maintain four bikes, and have a rule: any part that works loose twice gets blue Loctite on its threads. It has always worked for me--so far. A tube will last a lifetime. Available at your local auto parts store or Amazon.

Fred

[BrianW]

A good rule re: Loctite. Especially useful for small bolts that hold racks, etc. on. Just be sure to use the blue (removable) and not the red (more permanent).

[FredHiltz]

Yeah! The red is forever.

Fred