New life into an old shifter with 3d printing

[chris667]

Hello
I'm fettling an old mountain bike at the minute. It has an (unobtainable) 7s Suntour rear cassette on the original wheel.

I have a nice 8speed cassette on a Shimano hub, and I was thinking what a shame it is to have to replace the shifters.

Then I started thinking... has anyone replaced the little washer inside one with detents in the right place for a Shimano 8s cassette? It would be great if that was possible. I bet you could make one on a 3d printer. I imagine 10 or 11 speed would even be possible.

Has anyone done that before?

 

[cyberknight]

7 will work with 8 speed cassette if I remember rightly as the gear spacing is very similar,just won't be able to access one gear.

 

[Ajax Bay]

As said, just fit it and ride, deciding whether you want to use/lose the largest sprocket or the smallest. The centre-to-centre spacing is as @cyberknight says, very similar (5.0mm cf 4.8mm) so a minor tweak make it work smoothly is to ensure that selected sprocket 4 (on the shifter) is dead on.
https://sheldonbrown.com/cribsheet-spacing.html

 

[chris667]

Hmm. Not being able to access one gear is quite a big deal.

 

[DCBassman]

What brand/model are the shifters? If Shimano, there were several models that had both 7 and 8 speed versions.

 

[chris667]

I probably didn't phrase that question very well.

They are Suntour Powerflo thumb shifters. 7 speed.

I want to use them with an 8 speed Shimano cassette. I've slept since I last did this but I was under the impression that the spacing between the sprockets was different

I am really just speculating that the detents could be put into a different place with not too much issue and a 3d print. A cheap way to get flawless indexing with old thumb shifters, and you could even have 10spd if that's important to you!

 

[T4tomo]

Hmm. Not being able to access one gear is quite a big deal.

Really - depends how you look at it?

at the moment its 7 speed with your favoured suntour indexed shifters.

if you fit an 8 speed cassette, its still 7 speed with your favoured suntour indexed shifters

Why is that a big deal?

 

[chris667]

if you fit an 8 speed cassette, its still 7 speed with your favoured suntour indexed shifters

I'm never really sure if you're deliberately being obtuse.

A shifter that can't access all the gears on your cassette is really stupid.

 

[T4tomo]

I'm never really sure if you're deliberately being obtuse.

A shifter that can't access all the gears on your cassette is really stupid.

I wasn't been obtuse, i was pointing out that you would still have 7 gears, same as now, and depending on range of your 7 speed vs 8 speed cassette, arguable no difference.

i.e. say 7 speed 14-25, and a 8 speed 13-25, just index the 8 speed so it misses off the 13T sprocket?

There is no real advantage for the leisure cyclist of 8 speed over 7 speed.

"an old MTB" suggest its a triple up front so you have a massive gear range anyway.

EDITED to add , I'm not in any way offended by the obtuse comment, it was clear you just didn't really get the point I was making.

 

[Ajax Bay]

Really - depends how you look at it?
at the moment its 7 speed with your favoured suntour indexed shifters.
if you fit an 8 speed cassette, its still 7 speed with your favoured suntour indexed shifters
Why is that a big deal?

I'm never really sure if you're deliberately being obtuse.
A shifter that can't access all the gears on your cassette is really stupid.

Uncalled for, Chris
Think you should take care not to abuse people (calling them obtuse) because you fail to comprehend the entirely valid point that Tomo is making (and I had implied).
Anyway you say "A shifter that can't access all the gears on your cassette is really stupid." Well in that case don't use the "stupid" shifter.
We don't know what sprocket range the 8sp cassette offers but shall we guess 12-28t? Just index the derailleur to go 12-25. I assume you have a triple 44-32-22 say, so you will have a low gear shorter than 20 inches.

 

[DCBassman]

To answer @chris667 's question directly, I think it might be do-able, but not worth it. I would see if therte's an 8-speed version of your shifter, or change both to something else, it will be easier in the long run.
For what it's worth I also entirely agree that running a 7 from an 8 is a very poor setup unless no option.

 

[JhnBssll]

The 7 speed shifter would have to pull enough cable too, are the pull ratio's the same? Presumably they are if the cassette is the same overall width. I'd say it was possible, but might not last long. 3d printed parts aren't the most durable in this sort of situation.

 

[si_c]

You could switch the shifters to friction mode if they have it, put the indexing issue to bed entirely.

Edit to add: It's very unlikely that you will be able to convert the shifter to 8 speed indexed shifting, 3D printing the ratchet part replacement is unlikely to be accurate enough for it to work and really unlikely to be reliable enough for long term use.

 

[matticus]

I'd say it was possible, but might not last long. 3d printed parts aren't the most durable in this sort of situation.

That was my hunch - although I'm still learning about the capabillities of 3D-printing!

[ As an aside, I recently read somewhere about someone getting a batch of indexed ratchet-thingys made up to convert some classic shimano shifters; so that is possible, but probably a non-trivial undertaking! ]

 

[chris667]

Interesting, thanks guys.

Taking a shifter apart, I see that it is a not particularly complicated looking washer with dimples in spaces which correspond to the right position for the mech. The top of the shifter has a tiny bearing and a spring. I can see soft plastic wouldn't work well in that situation.

A big part of this is I would really like to learn about 3d printing and go down another rabbit hole.