About to put a parts bin special together and want to use my 92-ish DX 7 speed thumbshifters with a 2003ish Acera mech on a (probably) 8 speed cassette.

Obviously it wont work “indexed” but I’m assuming it’ll be OK set to friction – no problem with the range?

c,

It should work, even in indexed mode as the cog spacing is very similar.

8-Speed used a 135mm frame drop-out against 130mm for 7-speed.
Obviously you will only have enough indexing for 7 speeds.

If you run it in friction mode you will probably get all 8 or 9 on the range.

It will not index with 9-speed as they have crammed 9 cogs in the space of 8 on the same freehub.

PaulD

Wasn’t there an 8th position on them?

Otherwise what he said.

Cheers, thought I had a vague memory of there being an “extra” click, will whack it on and try it, can always leave it on friction I guess.

Used to be quite common to use them with an 8sp cassette at one time, there was enough leeway for them to index acceptably, but not absolutely perfectly.

Obviously you will only have enough indexing for 7 speeds.

wrong for shimano. They famously put 7 indexes in (you only need 6 indexes for a 7 speed block, think about it) so it works with 8spd. Munqe Chick still has a ’94 Kona with shimano thumbies kept as a mud/winter bike which I put an 8spd cassette on years ago and it works perfectly with careful set up (which is why it was so common a sight).

Should work just fine ime

er…

They famously put 7 indexes in (you only need 6 indexes for a 7 speed block, think about it) so it works with 8spd.

I think you’ll find they “put 8 indexes in”
8 positions = 8 stops in the index plate = 8 “indexes”.
take yours apart if you don’t believe me, you can’t simply ignore the stop the shifter is sitting at to when you count them. (well.. you can but it would seem incredibly dumb to do so)

Still using 6 & 7 speed here…

As above – 7 & 8 spacing is slightly different. 6, 7 and 8 speed cogs are the same thickness. 9s are thinner.

So if you can scrounge some 7 speed spacers out of a worn out cassette you can get it exact.

Ta, little job for the weekend.
Quite looking forward to trying them again!

Retro Shimano 7sp thumbies with 8 speed block no problem – the top pulley floats a little so I can’t see a fraction of a mm being any issue.

PaulD – Member
c,

It should work, even in indexed mode as the cog spacing is very similar.

8-Speed used a 135mm frame drop-out against 130mm for 7-speed.

Not always – plenty of 7 speed stuff was 135mm spacing.
But yes, it’ll work with 8 speed.