Bicycle Mechanics - Adjusting Cheap Indexed Gears

My g/f has a $300 Scott mountain bike, with one or other cheap Shimano (I think) indexed gear system with nasty gripshifts. I've read up how to adjust derailleurs in general, getting the limit screws right, but how do you make sure that you're shifting right? Is there a trick to getting it nice and quiet in all the gears?

Most gear tuneing is done with cable tension adjustments. The cable tension is adjusted with a barrel adjuster usually located where the cable enters the rear derailleur. With most bikes you set the cable tension for the smallest rear cog first, then run through the gears to see if any fine tuneing is necessary to get quiet opeation in all of them.

If that doesn't work, most times it's because the derailleur hanger has gotten bent. For most people I'd recommend taking the bike to a shop because they'll have a gauge for adjusting the hanger. It's about a $15.00 or $20.00 job.

Once the limit screws have been properly set adjusting them is almost always a mistake.

Yes - there's no problem with the limit screws. Thanks for that - she took it to the LBS and got it adjusted, but I want to be able to do it next time. And I've got a POS MTB of my own that could do with a tweak........

Don't touch the limit screws if they are perfect now. Adjust the cable tension using the barrel adjuster on the rear derailleur.

http://parktool.com/repair/readhowto.asp?id=64

Parktool will help you out with any repair problem that you have.