Not about anything interesting to you probably I expect
I'm posting this and leaving it unlocked so that if some poor sod finds himself in the same position as me and Googles the same keywords as me he may find this post and have all the info in one place rather than spend DAYS searching the interwebs for the correct information.
About two years ago I was building up a time trial bike, and wanted to have bar end levers on the ends of the tri bars so that I could change gear whilst still in the aero position. I was running Campagnolo 9 speed at the time. I couldn't find any 9 speed bar end levers in the shops but luckily found a used pair on e-bay. £70 later (new ones are over £100) and I had them in my paws.
It was a few weeks after this until the bike was ready for the road. I'd had to buy bits as I could afford them. As soon as I started riding there was a problem. The gears wouldn't index properly. One click of the bar end lever would make the gear change 2 or 3 gears. I took the lever apart and compared it to the exploded drawing on the Campagnolo website. It was all fine, exactly as per the drawing. I put it back together. It still didn't work properly.
I started searching the internet and found a forum with a discussion similar to my problem. One comment rang alarm bells as it said that Campagnolo never made 9 speed bar end levers, only 8 or 10 speed. By this time it was way too late to return the bar end levers to the ebay seller, and so they went into my parts bin and I solved the gear changing problem in a way that I won't go into here as it involves Shimano *spits*.
Now fast forward to the present, and I'm building up a new full carbon timetrial bike. As I have 10 speed bar end levers I thought I d build it up with Campy 10 speed gears. So I get it all built up, take it out for a test and... the gears don't index properly. I've got nine clicks on the lever indicating that there's 10 gear positions, which is a good thing, but it skips a couple of gears on its way through the block. Puzzled I went back to searching on the internet.
Inside the lever is a small ratchet cog which clicks the cable at the right place to change the gear. On this cog is an arrow and it turns out that the arrow has to be pointing in the same direction as the lever. If the lever is at six o clock, the smallest cog on the block, then the arrow has to be pointing at six o clock as well. I took apart my lever and found that the cog was not fitted correctly. I took it out and after some fiddling and swearing refitted it correctly. I rode the bike again. This time it was even worse, and oddly one click had disappeared. It was now behaving like a 9 speed bar end lever. Back to the internet.
It turns out that you can buy these little ratchet cogs, and that they come in 9 or 10 speed versions. That explained a lot. I had the nine speed version, but when I'd tried it on my 9 speed gears 2 years ago the ratchet cog had been fitted incorrectly and so didn't work. Now it was set correctly but I was trying to use a 9 speed lever on a 10 speed bike. I looked on the Campagnolo website and found the phone number of a UK distributor. Gave them a call. 10 speed ratchet cog in stock. £7.
So that's that. It has been very frustrating trying to work out why something apparently simple wouldn't work and it turns out that it's because I'm a dullard. Hopefully anyone else finding this will save themselves a lot of time and swearing. Just for good measure, the part number of the 10 speed ratchet cog is SL-RE319, and the 9 speed version is SL-RE219. Phew!