UKC

Long overdue maintenance so new chain and then later wanted lower gear so new cassette 11-36 replacing 11-32. 

Rear mech spec is max 34 sprocket but tightened B screw and seems ok.

Did not lengthen chain but top and bottom sprockets both ok with both big and small chainrings.

Indexing ok.

One of the middling gears on the 9 speed cassette feels rough for both big and small chainrings. Other sprockets feel ok.

Funny it's not a sprocket at the ends of the gear ranges or cross chaining issue.

Any ideas?

Cassette spacers might have some dirt between, making the tightness inconsistent.

How long did you run the new chain before getting the new cassette? Running a new chain on a well worn cassette is a sure way to reduce its life.

New cassette days after new chain.

It's the middle gear of 9 so in a solid block of 7 with two smallest sprockets loose. I don't think the 7 come apart.

Update - maybe I just needed to tighten b screw more. Will give it a test ride during the week.

Thanks for the tips.

Cheap 9 speed cassette for anybody wanting to try 11-36.

https://www.decathlon.co.uk/p/cassette-9-speeds-11x36-microshift/_/R-p-1987...

If this is the cassette you used, if you look through some of the reviews of microshift cassettes there are other reports about the same problem with indexing in the mid range. I need a few new cassettes (one 10 and one 11 speed) due to a momentary lapse in maintenance and after seeing that a 105 11 speed cassette is now £50+ considered microshift but have been put off by the reviews on decathlon. Their higher spec cassettes get better reviews but are hard to find and ~£40 so not that much cheaper than a tested Shimano offering.

Oh bugger! That's not good.

What is good, if you bought it in decathlon, is that they seemed to be offering refunds to people who were complaining about them on the website. You may need to use Google translate to read the reviews but if you have a look at the low rating reviews with replies from decathlon you may be lucky.

11-36 over 9 gears - the jumps must be massive!

I always use a rear mech alignment tool before indexing gears. Poor indexing in the middle of the block is often a symptom of a slightly bent mech hanger. 

So's the gradient!

Anyway, not really. No worse than an 11-32 8 speed I'm used to.

Funnily enough I have a similar issue. My bike is still on the original 9 speed 11-36 cassette, so a genuine Shimano one. I've always heard a bit of a whirring when using the 5th cog, despite fiddling with indexing and everything else. It's the same with either chainring. It's only the one cog that does it and it's very minor so I've just got used to it.

I found my mid-range shifting improved massively after replacing the gear cables. Not saying that's definitely your problem but might be worth doing if you've tried everything else.

I also replaced cables. This all counts as major maintenance for me!

Had this with several causes in the past.

• Gear cable either stretched or not routed correctly into the derailleur anchor screw. Had this after I re attached the gear cable, the screw had rotated and the groove for the cable wasn't correctly placed.
• Front derailleur misaligned. I thought it was the rear but actually chain had been catching the front when even slightly cross chaining.
• Gear cable requiring replacement. Check the cable in the shifter, might be frayed and barely hanging on.
• Derailleur alignment issue from a bent hanger.
• Could just be a cassette/chain mismatch of one is newer. 

Good luck!