Can 7sp XT SL-M732 Thumbies shift 8 gears?

[Peachy!]

Hello lovelies,
I’m got an opportunity to upgrade my ‘91 XT clad Antaeus with some ‘92 XTR M900 bling, but as I want to keep the Maguras I won’t be swapping out the brakes.
So the question is, will my current 7sp XT thumbies shift the extra gear or do I kneed to get a set of 8sp rapid fire XT ST-M008 from ‘96?

 

[legrandefromage]

yes, but not great, but yes

 

[retrobikeguy]

Thumbies'l work fine

 

[mk one]

Yes they will work on 8spd.

 

[legrandefromage]

index them to the bottom cog as if its a 7spd, the extra 'click' then lobs the chain upstairs to the last big cog

 

[ishaw]

I ran xt 7 speed thumbies with 8 speed m739 stuff and it worked very well. No indexing issues, just nice crisp, reliable shifting.

Makes you wonder why thumbies don't really exist anymore, though as things are being reinvented, surely it can't be long before they make a comeback.

 

[nodding dog]

The centre-to-centre spacing on 7 speed is 5mm and on 8 speed it's 4.8mm. Some folk reckon this makes a difference but personally I've never noticed it. It can be mitigated by adding a smidge more cable tension so that the indexing in 4th and 5th is spot on and the cumulative error in 1st and 8th won't be noticeable.

Makes you wonder why thumbies don't really exist anymore, though as things are being reinvented, surely it can't be long before they make a comeback.

Bikemonger sell Microshift thumbies now. I've just fitted one of their 10 speed thumbies to an old Cannondale with an 11-36 10 speed cassette and it works like a charm.

 

[slackboy]

I ran xt 7 speed thumbies with 8 speed m739 stuff

Just done this to my bontrager, no problems at all

 

[Mickeyspinn]

The centre-to-centre spacing on 7 speed is 5mm and on 8 speed it's 4.8mm. Some folk reckon this makes a difference but personally I've never noticed it. It can be mitigated by adding a smidge more cable tension so that the indexing in 4th and 5th is spot on and the cumulative error in 1st and 8th won't be noticeable.



Bikemonger sell Microshift thumbies now. I've just fitted one of their 10 speed thumbies to an old Cannondale with an 11-36 10 speed cassette and it works like a charm.

Crumbs I can't actually remember ...spent a lot of time a few years back modifying 8 speed blocks for 6 speed and 7 speed indexing..there was definitely a difference in cog thickness but I don't think it was as big as .1 per cog! With out going to measure I thought it was something like 2.39 thickness for 7 and 2.34 for 8.
I did find that replacing the plastic spacers with alloy did help in chasing out the tiny descrepancy at the top and bottom of block when shifting.

 

[Tootyred]

Works despite minor spacing issues.....real world ok.

My only reservation ( and this is not often mentioned) is the impact on the quality of the 7 shifting ability after its been 8 speeded too much.

They are not designed for this and the 8th click is the bearing running over the end of the indents on one side. As you will know, you dont have an 8th stop.....its the derailleur that stops it lobbing the cage into the wheel on the limit screw.

I do wonder if long term it weakens the spring and damages the plates / bearing every time its over driven.

People talk of a "hidden 8th" but why would it! 7 was new tech when these came out!

Just a thought

The other option is suntour.....which have switchable 7 /8 speed thumbies....essentially uncovering another indent.....although the spacing is still wrong!......but works too.

Heres one i gutted earlier......if you ever wondered what magic goes on inside....