Problem with cassette shim
 

I bought a wheelset that was 8,9,10 speed compatible and put a 7-speed cassette on with the requisite spacer. I got the spacer from my LBS. I had shifting and skipping problems on the 32 tooth sprocket and discovered the cause was gross runout. Turned out that the cause of the runout was that the spacer under the cassette had too big an inner diameter and would shift to one side and almost go past the shoulder on the hub. I have not had much luck finding other spacers with a properly snug inner diameter. I ended up dismantling another perfectly good -- but currently unused -- cassette and using the #3 gear plus a 1mm shim for the spacer. No runout whatsoever, shifting is perfect and no popping. Of course it looks very wrong and I have lost a perfectly good cassette to do this.

Any suggestions on where to find spacers with snug ID that will fit properly?

Don in Austin

Many 7-speed cassettes have the largest 5 or 6 cogs held together with bolts or rivets and the bolt/rivet heads can interfer with seating the cassette if the spacer is added behind the largest cog. You could remove the bolts but I had good results installing the 4.5 mm spacer between the smallest cog and the lockring which avoids the problem entirely.

I saw that, so I put the spacer on the grinder to make three little depressions where the rivet heads are. The problem was the entire spacer going crooked where it seats on the hub. I would probably have to change my bottom bracket if I put the spacer on the outside.

Don in Austin

I doubt it would change the chainline enough to make any difference. You would have to reset your rear derailleurs limit screws.

Doesn't the smallest cog have to stay on the outside edge? All my cassettes have a lipped small cog.
OP: PVC pipe?

The smallest cog does stay on the outside of all of the other cogs but it doesn't have to be right up against the lockring. The 4.5 mm spacer can be installed outside of the the smallest cog and the lockring can tighten down against it. The lockring, if torqued to spec, will remain tight with no problems.

some small cogs, mostly 11t cogs do not slide down the freehub body, their is a lip on the cog preventing this.

This is what I mean. I've never seen a cassette with a small cog that can slide down the freehub body-not even my seven speed shimano cassette. Perhaps some cassettes have a non-lipped small cog?(in which case the outer spacer sounds ideal).

OK, good point. I've never needed or used an 11T cog so I neglected to mention them as an exception. All of the 7-speed cassettes I've used started with a 13T cog and I never had any problems using the spacer outside of the small cog and under the lockring.

However, I just checked several 12 and 13T Shimano 7, 8 and 9-speed small cogs and all of them slid completely down over a Shimano 8-speed freehub body so they would all work with the outboard spacer too.