Hopper

I busted a shifter on my mountainbike with a 8spd derailleur and cassette. What I want to know is could I somehow setup the 8spd derailleyr to work with a 9spd shifter. My friend said he'd give me an LX 9spd shifter for $5 if I wanted.

phillybill

It will work, you just will not need/use the last position the LX has to offer.

roadfix

Your derailleur will work just fine with 9-speed shifters. You know you also have to replace your 8-speed cassette for a 9-speed for proper indexing right?

sydney

Derailers don't really have speeds.The 8 speed will work.But, you will need a 9 speed cassete and chain.

gruppo

Hopper, if you can get your 8-speed cassette apart you can exchange the spacers and use your existing cassette & chain. Your lbs might have or can get a 9-speed spacer kit (Depending on the quality of your cassette & chain, this might be a lot less expensive), or better yet the lbs or a friend might have a worn out 9-speed cassette they would give you and you could remove the spacers from it (Then it would be no cost). As has been said, your existing derailleur will work fine. Good luck!

Retro Grouch 

Now lets all think this through because some of this advice is just wrong.

8-speed and 9-speed cassette spacing is different. A 9-speed shifter won't work with an 8-speed cassette because it only pulls enough cable to move the derailleur for the shorter 9-speed spacing. If you try, what will happen is that it will work fine in the 1st and 8th gear positions. In between, in the gears that you use most, it's going to be noisy on every one and will skip a shift somewhere in the middle.

Because the 9-speed cassette has the cogs spaced so closely together, an 8-speed chain is too wide to work. It will rub adjacent cogs. If you use a 9-speed cassette, you'll also need a 9-speed chain.

I suppose that, on the lower priced groups at least, it might be possible to respace the cogs from an 8-speed cassette to 9-speed specs. It wouldn't be as easy as you might think, however, because the cogs themselves are also a slightly different thickness so stock 9-speed spacers will be too thick. If somebody made a kit of spacers the right thickness you could block off one of your shifter positions (you'd actually do that on your derailleur) and that would work. You'd still need a 9-speed chain because now you'd have 9-speed cassette spacing. Honestly, I don't see the point of doing that. I certainly wouldn't.

All of this talk of 8 and 9-speed chains brings up yet another issue, the FRONT derailleur. 9-speed front derailleurs have a slightly narrower cage than ones that are designed with an 8-speed chain. I've never tried using an 8-speed front derailleur with a 9-speed chain on a mountain triple, but I can tell you that it doesn't work to my satisfaction on a road triple.

If it was my bike, since you have to replace the shifter anyway, I'd take this opportunity to upgrade it to 9-speeds. I'd buy the bargain shifter, assuming it didn't look trashed, and brand new 9-speed chain, cassette, shift cable and housing. Your rear derailleur will be fine. Then I'd put it all together and go for a ride to see how the front derailleur works with the narrower chain. That's what I would do.

Good luck.