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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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1 Answer 1

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 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 at 19:38

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