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I just got a bike with broken hanger and derailleur. As the owner didn't want to put money in good parts, I installed a cheap Sunrun derailleur compatible with index, and a new hanger. Just after I finished the work, adjusting the cable I noticed, that it have 8 speed shifter and 7 speed cassette. I know, that it's not an issue, and there is no problem to adjust it normally and I left the 8 as ghost, but this time I couldn't adjust it: if all the gears shifting up good in 7 > 1 direction, they will not shift good down (1 > 7) and vise versa. There is a point that both directions not shifting well, like remain at gear 7 while shifter showing 6 and remain at 1 while shifter showing 2.
Am I missing something? I cleaned and oiled the shifter, cleaned outers, put a new cable and new derailleur.

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2 Answers 2

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Like you say - the 8 speed shifter will work perfectly well with a 7 speed cassette. You just lose the use of 1-click too many. Poor shifting in the downward direction is usually a sign of poor cabling. Either old cables or poor routing. But you mention poor shifting in both directions - which looks suspiciously like a problem with the shifter itself.

Mark an exposed area of the gear cable and begin to shift up. You should see the cable move proportionally by the same amount each click. Now shift back down - you should see the cable move back to its exact original position. And this movement back down - should be instantaneous with no slack in the gear cable.

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Yup. I already forgot about that question, but there were really poor shifters (which were replaces). –  Alexander Feb 5 at 0:05

Assuming the shifter and derailleur have compatible cable pulls (which you should check), you won't be able to perfectly adjust the shifter to shift smoothly on a cassette of 7, since the cable pull which moves the shifter for 8 speeds is likely not enough for 7 speeds. Thus, generally, you need to match the shifters with the derailleur and the cassette spacing.

Sheldon Brown has some comments on 7 speed setups and running an 8 speed shifter with 7 speeds through some alternate cable routing, but given that you can buy an 8 speed cassette for like 10 bucks, it seems like an unnecessary hassle (given the extra time you'll be spending tweaking adjustment). Or you can bolt on a 5 buck friction shifter and save yourself some time too.

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Thanks! I'll try to change the cable routing. Unfortunately, the cheapest cassette here costs 20$ - 25$, and it's not called cheap here. The shifter is EZ fire, so replace it will cost about 40$... The owner as I wrote do not want to put money onto this bike at all but to make it "rideable". –  Alexander Jun 7 '14 at 19:15
    
Worst case, you're stuck with 1 speed anyway - just get the chain on a compromise cog in the middle (maybe a 15t or something if you're running a 42 in front), and leave ti there without shifters. –  Batman Jun 7 '14 at 19:38

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