Can I Fix My Indexed Shifter?

July 12, 2007 8:37 PM

My new-to-me Schwinn Frontier mountain bike's indexed shifter for the rear gears is unwell. Help me nurse it back to health.

I got a great price on a used Schwinn Frontier mtb, in part because the shifter doesn't want to downshift below 5th gear on the rear. It's a Shimano indexed "pull with index finger to shift up, press with thumb to shift down" sort of shifter, integrated with the brake lever. When you press the "shift down" lever in 5th gear, there's no tension/resistance on the lever (as in the higher gears) and nothing happens on the rear end. I suspect something inside is mucked up.

I'm not horribly concerned because I plan to use the bike mainly for short-range commuting and my commute is 100% flat (so high-gear appropriate) but I'd really like to fix it so I can take the bike off-road with friends. Google shows a lot of depressing Shimano repair attempt stories. Should I take it to a bike shop, try and fix it myself, or just give up and live with a 12-speed instead of a 21-speed?

posted by Alterscape to travel & transportation (6 comments total)

Your rear deralliur (sp?) might be just be incorrectly set up. Disconnect the cable to it and set the shifter into highest gear.

If you put tension on the cable (i.e just pull it) and start to downshift do you get 4 or seven clicks? If you can shift up and down 7 times using this manual setup your shifter is fine and you can just put everything together again. Read a guide on how to tune your gears first. If you only get 4 your shifter is broken. Buy a new or used one and just replace it.

The bike shop can do all this for you of course but you will learn useful basic maintainence skills doing it yourself. Good luck!
posted by uandt at 11:44 PM on July 12, 2007

Hmm, by no tension do you mean that you push the thumb lever and it moves easily but nothing happens? That's pretty strange. The usual problem for not shifting in to lower gears is either cable tension or badly adjusted limit screw, both of which would show up by you not being able to move the lever.

If you turn the bike upside down and turn the pedals with one hand can you get it to shift another gear by pushing the derailleur with your hand?

Might be easier to take it to a shop, it probably needs new cables anyway.
posted by markr at 11:49 PM on July 12, 2007

This is a guide to rear-derailleur adjustment by the way. The important bits are the L and H (low and high duh) limits and the indexing (cable tension) adjustment. Don't worry too much about the B screw. Do them in order, there isn't much point messing with cable tension if your limits are way out.
posted by markr at 11:52 PM on July 12, 2007

sheldon brown's article is probably better. i second the possibility that the cable may need to be replaced if it's worn. that's pretty likely with an index shifter. shouldn't be too hard to replace if you're committed to repairing things on your own.
posted by lester's sock puppet at 6:01 AM on July 13, 2007

I'll third that the cable either needs to be adjusted or replaced.

Although -- be aware that the gears might also be a bit warped. I've seen this happen with a *lot* of bikes on the campus where I work. If the teeth have gotten bent by someone reefing on it or chucking the bike in the bed of a pickup truck or something else stupid, then that would be another reason why it isn't working.
posted by SpecialK at 7:04 AM on July 13, 2007

There is no tension on the shift lever, but is there tension on the cable?

If the cable is tight..

My rear shifter cable always fails by fraying a little inside the index shifter. When this happens, I get the exact symptom you describe. Because it is only fraying a little (one or two broken wires), it mostly works, but.. As you let the cable out, to get to the smallest cogs, the frayed wires jam in the narrow workings.

If the cable is loose..

You need to adjust the low gear stop position, see Sheldon Brown.



New cables, and casing, will make it shift much more smoothly. Cable and casing can be hard to cut with typical household tools, but it turns out Dremel cutting discs do a pretty good job.
posted by Chuckles at 9:37 AM on July 14, 2007