Shimano 105 5700 - which spacers

mikeeye

I'm looking for opinions and advice re some weirdness with a new cassette...

I've just replaced the cassette on my RS21 wheel, using both the thick spacer that came with the wheel (1.85mm?) and thin spacer that came with the new cassette (1mm?). After doing this I found that the gears were skipping and I couldn't cure this using the adjuster on the rear derailleur as it hit the limit. I undid the gear cable to adjust this and while it was disconnected I found that the two extremes for the rear derailleur were not lining up well with the cogs.

All had been working well before the new cassette (and chain) though it was beginning to skip a little due to chain wear.

I have now removed the thinner spacer and that made things line up pretty well - only slight adjustment needed on the H and L screws (1/4 turn at most).

So what am I missing? I had both spacers on with the previous cassette, so why not now? With the new cassette and just the thicker spacer, the chain seems well clear of the spokes and the frame, but should I really be using both spacers and making the necessary adjustments on the H and L screws? Or have Shimano perhaps changed the cassette slightly. A search here revealed this related post which indicates that a Tiagra cassette doesn't need both shims. Maybe 105 has been brought into line with that.

I'm leaning towards thinking it's fine as I have it on the basis that the cassette must be aligned very closely to how the previous cassette was - otherwise I'd have had to make bigger adjustments on the H and L screws.

Thanks.

andy_wrx

If it works, leave it like that

If the 1mm 10sp spacer came with the cassette, that's how it always was. A Tiagra cassette wouldn't come with one, or need it.

svetty

Assuming that you have replaced the old cassette with one of the same spec (105 5700?) then the indexing shouldn't change - assuming the lock ring is torqued properly, you have included all the cassette sprocket spacers, and the sprockets are properly seated on the freehub.

The 10 spd Tiagra 4600 cassette doesn't need the 1mm spacer but the remainder of the 10spd shimano cassettes do.

The hangar might be out of alignment or the derailleur bent, but this should affect both old and new cassettes equally.

Given that the correct chain-line assumes both spacers are fitted, then assuming you're sure you have mounted the cassette correctly (with both spacers) then I'd adjust the limit screws and cable tension to optimise shifting with both spacers in place - this is how it's meant to be installed.

mikeeye

While I like Andy's "if it works, leave it" advice, I guess the fact that I posted the question shows that I wasn't really happy about having a spare spacer, so I've followed Svetty's advice and assembled it properly and adjusted the limit screws as required. Not sure how important 1mm can be for chain line, but I'm happier with it assembled as per the instructions.

Thanks for your input Andy and Svetty.