loose cassette lockring (6700)

[Ben M]

My mum's bike had a mystery noise. We tried the usual suspects like bottle cages, spokes etc. to see if they were the cause, to no avail. I grabbed the cassette, and discovered that the smaller sprockets could move a little, independently of the large ones.

I came to take off the cassette, and I didn't need my lockring tool: I could have taken it off by hand, it was that loose. The inner teeth of the cassette look fine, the hub (DT Swiss) splines aren't perfect, but aren't too chewed up. I re-fitted the cassette and tightened the lockring up tight, and now it seems fine...

The bike was in a crash not long ago, and took a rear-end NDS bang on the quick-release, so that might be related. The bike/cassette isn't that old, it is on its first chain which is nearly at the first wear thingy on a chain checker, but not quite so a few thousand miles in (it is well looked after in the clean & lube department).

So... What could have caused this? Is something broken that I don't know about? Was it not tight enough to begin with? (the bike was built by the shop) Might the crash have caused it to slip? Will it be okay now?



Obviously I'm going to keep an eye on it to see what happens next...

 

[02GF74]

it came undone as it wasn't tightened enough; nothing to do with crash.

 

[Colin S]

Strangely for the 1st time I used a torque wrench a few days since when I put my new cassette on. It is very tight if you use the Torque recommended.
Much tighter than I would normally have tightened it to, so I guess yours just wasn't tight enough originally.


C

 

[john59]

I always torque my cassette lock ring to the required torque, 40 N·m. I remember a colleague who had changed his cassette for a sportive and had not tightened it sufficiently. The lock ring came adrift half way round the course. We managed a bodge job using a screwdriver to rotate it slightly, but his gears were all over the place.


John

 

[Ben M]

Okay, thanks guys. So it looks like it was down to the original torquing. Like I said, I'll keep an eye on it and see if it loosens again.

I've always said that the major downside to BMCs is that you can only buy them in one chain of bike shops... Whom I never really rated, and certainly don't now!