New Cassette is loose
 

I am putting a new cassette on my wheel.

the wheel is a Mavic Ksyrium Elite, and the cassette is a Shimano Ultegra CS6600 12-27.

The Cassette came with two very thin spacers, one that goes before the largest cog, and one that is right under the lock ring.

I have both of those in place.

when I took the old cassette off, it seemed like, (but I am not 100% certain) there was another spacer behind the largest cog. this one is quite thick - maybe 1.5mm, and looks just like the spacers that go between the cogs - it has the same teeth to engage the spindle (or whatever it is called).

I was not aware that there was ever a need for a thick spacer like that, and the Shimano documents don't show one.

Should I just use that spacer anyway?

Is there something else going on?

The cassette is quite loose - if i shake the wheel, I can hear all the cogs jingling....

It takes considerable torque to fully tighten a cassette lockring, in part because there is
a sort of ratchet mechanism under the lockring to keep it from loosening. Torque needed
will be in the cassette info, but absent a torque wrench try rotating the lockring another
1/4-1/2 turn. If it still rattles you may need that thicker spacer if you still have it.

OK, I tried it with the thick "extra" spacer, and the two thin spacers that came with the new cassette.

I couldn't seat the lock ring...

So, I tried it with the two thin spacers that came with the new cassette, and an extra thin spacer from the old cassette, placed under the largest cog.

This worked..., except..., even when _really_ tightened down, I can wobble or tilt the cassette back and forth, ever so slightly on the spindle with my hands.

it doesn't seem like there should be any play at all...

maybe only use the thick spacer and not the thin spacer?

use the mavic spacer(~1.5mm) and the shimano 1mm spacer

i would find the combination that allows the lockring to tighten down without bottoming out. whatever that is and go from there.

why? because if you can't get the lockring on, you're in trouble and if the cogs rattle, you're in trouble. so why not start with at least a chance of being correct?