I have some old 7speed topmount deore shifters on my an old Kona. They have what seems to be a 'phantom click' i.e. there are actually 8 positions but the last one moving from the 7th to the 8th doesn't actually move the mech.

I'm currently planning a majorish overhaul: wheels, cranks, mech, cassette, chain etc and would like to go to 8speed. I'd also like to keep the shifters as (a) I like them and (b) it's save me a few quid.

Anyone know if that last click means they can be used for 8speed? Anyone done it? How did you get on?

Yes indeed - that phantom click will offer you an 8th gear

Or it will if you're lucky. I might be unnecessarily picky, but I've never managed to make this work to my satisfaction. Centre-to-centre, 7spd sprockets are 5mm apart but 8spd ones are 4.8mm. Now that doesn't sound like a lot, but it adds up across the width of the block. The trick is to set the indexing in the middle of the cassette (where you are most of the time) in the hope that the cumulative error doesn't get hopelessly big by the time you get to the ends. Plenty of people have made it work, but as I say I've never been happy with it, especially as you can still get perfectly satisfactory 7spd cassettes ;-)

Of course you can shift 9 speeds with them too if you run them in friction mode.

Mike is right that the indexing isn't that great though. But if you will insist on using thumbies......

Maybe I'm just lucky, my 8spd setup works fine with XT thumies