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-   -   Shimano STX rear derailer problems, won't shift onto highest or lowest sprocket (https://www.bikeforums.net/bicycle-mechanics/938241-shimano-stx-rear-derailer-problems-wont-shift-onto-highest-lowest-sprocket.html)

General Geoff 03-14-14 02:02 PM

Shimano STX rear derailer problems, won't shift onto highest or lowest sprocket
 
I have an old '98 Kona Fire Mountain that's had some rough usage in the past. While the bike is way too small for me to ride, my girlfriend likes to ride bikes with me, the kona fits her nicely, and it's nice to have a spare bike here for her to ride when the whim strikes. We took a ride a few days ago and we found that she could not shift into the lowest or highest gear in the rear. I've been tinkering with it for an hour, trying to adjust the derailer every which way, but it refuses to move far enough to engage either the big or small sprocket. Doesn't matter how much I tighten or loosen the shifter cable, or how much I adjust the set screws. This is on a 7 gear cassette, it's an old Shimano STX derailer. Is it time to replace it with a new derailer? If so, what would work well with the bike? Not looking to spend lots, but would like something that'll last at least a few thousand miles.

I can take photos if needed. Thanks :)

AnkleWork 03-14-14 02:14 PM

Have you checked the straightness of the hanger?
Have you setup the derailleur from first principles, as though a new install?

Retro Grouch 03-14-14 02:19 PM

Honestly, I doubt it's the derailleur.

Since you have a 15 year old mountain bike that has seen some rough usage the first thing that I would do would be to check the alignment of the derailleur hanger. Then, while I had the derailleur off I'd try to cycle it with just my fingers to see if it is moving over it's whole range. Check the shifter to be sure you are actually getting 7 shift positions. Finally I'd reconnect the shift cable and see if you can get all of the parts to work together.

cny-bikeman 03-14-14 02:20 PM

As you have discovered, random tinkering is not a good approach. A new derailleur won't help if you are taking an incorrect approach to tuning it. In addition to the inner limit screw, too loose a cable will prevent shifting to the large cog, not only too tight an outer limit screw but also a bent-in hanger or too much cable friction can prevent reaching the small cog. A bad shifter can cause either problem.

If you want to keep trying it on your own Google adjust rear derailleur, skip the videos for now and go through the procedure on parktool.com/blog and/or sheldonbrown.com - but keep in mind that correct shifting depends on the shift cable and lever as well as the derailleur. Standard index derailleur procedures apply. Go through from start to finish, using videos to see the procedure live once you understand the written instructions.

I'll give you one quick hint - try backing off the low limit screw and then (carefully) shifting to the large cog by pushing in directly on the derailleur - bypassing the cable. Loosen the cable completely to see if it reaches the small cog when you back off the high limit. If both work that way it's not the derailleur.

OR

Bethlehem Bicycle Cooperative
1935 W Broad St, Bethlehem, PA 18018
(610) 954-5744

I'm surprised you would not seek out them immediately - only about 4 miles from downtown Allentown. I would expect that the $55 for the membership that gets you access to the shop and tools is well worth it.

General Geoff 03-14-14 02:36 PM

I wasn't randomly tinkering, I carefully marked the original positions of everything and methodically adjusted one thing at a time, checking function between each adjustment.

That said, I'm beginning to think it's not the derailer either; the shifter only indexes five positions, not seven. :(

cny-bikeman 03-14-14 02:47 PM


Originally Posted by General Geoff (Post 16578132)
I wasn't randomly tinkering, I carefully marked the original positions of everything and methodically adjusted one thing at a time, checking function between each adjustment.

That said, I'm beginning to think it's not the derailer either; the shifter only indexes five positions, not seven. :(

Great that you were methodical, but no way to tell that from the original post...

Originally Posted by General Geoff (Post 16578037)
... I've been tinkering with it for an hour, trying to adjust the derailer every which way...

The co-op says it has used parts so that's an option for the shifters but you can also try flushing out the shifter with solvent. Don't assume the number of clicks is incorrect until you have disconnected the cable. If it is too tight you won't reach the last click. For a 7 speed there should of course be 6 clicks from the relaxed cable position.

General Geoff 03-14-14 03:12 PM

SOLVED!

I took the shifter off the bike, removed the cover and checked function. Apparently the pawl was stuck in old dried-up grease, and wasn't fully engaging the cogs. It was pushing on the stop, which allowed it to shift up to four times with a single push through the entire range, but after ratcheting back, it would skip over the cogs when trying to advance the gear further, until it reached the end of its range of motion. I put a few drops of CLP in the pawl mechanism, and that freed it up so that the pawl now fully engages on all cogs. Working with all seven sprockets again!

Thanks for the help everyone. :)


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