Help! Slow/ghost shifting problem driving me crazy!
I finished assembling and have been riding for the past 6 months (~3 hrs/week on local singletrack trails) a Giant Trance frame-up build, including a new '07 SRAM X.9 rear derailleur, new SRAM PG970 cassette, new SRAM PC99 chain, new cables, etc. About a month ago, a branch got caught in my rear wheel and twisted/bent the derailleur cage and hanger/dropout. I replaced the dropout, the cage wasn't too bad so I straighened it myself, everything appears to be straight and moving as it should. Since then, the bike has been shifting poorly (lots of sluggish shifts and some very delayed shifts), and I can't figure out what's causing the problem.
It shifts a little better on a workstand (under no load) but still not crisp like it was before. I've adjusted the cable several times, trying to find a 'sweet spot', to no avail. The cable is adjusted correctly (lines up w/each cog), but for some reason, the chain seems to want to stay on a cog for awhile after I shift to the next cog. (I can see the derailleur is clearly moving over to the next cog while the chain stays for awhile on the prior cog.)
I'm considering replacing the derailleur but would rather avoid spending $80+ to possibly find out that the problem is being caused by something else (chain, cassette, etc.).
So before I resort bringing the bike to my LBS (and more importantly, admitting that I can't fix it myself - a tough realization for a mechanical engineer who's built and maintained his own bikes for years), does anyone here have any similar experience and/or suggestions?
No expert just learning myself.
Does your chain have too many links?
Have you adjusted your "B" screw on your rear derailleur?
Trek 4300 2006
M580 LX cranks
El Notre 7075 Seatpost
Laser V saddle
Thanks for your suggestions.
Originally Posted by MillerSHO
I'll be sure to re-check chain length, but I'll be surprised if there's too many links - I was very careful to set it and the rear derailleur up to handle both extreme ends of the gear range. Besides, I've since abandoned/disabled the small and big rings up front (using only middle ring), so I'm running only in the middle range of chain length requirements.
I'm not familiar with the term, "B" screw, but by process of elimination, I'm assuming it's the one that touches the frame (dropout). If so, I have not readjusted it since initial installation. Is there something I should be looking for there?
stiff chain link can be a real common issue in this case as well, might want to swap in a new chain
When the cause of shifting problems isn't clear and you're determined to sort it yourself, a process of elimination is your best course. Do the free stuff first. Any foreign bodies in the derailleur? I once had a bunch of crushed up grass seed seriously clog up a derailleur. With the derailleur still attached to the hanger and the chain out, manually move it through it's range of motion. How does the chain feed through when you spin the cranks quickly backwards? Does it skip about or sound chattery? Spin backwards again, this time slowly, and watch the chain as it passes over the smallest gear on the cassette. A stiff or damaged link should rise up as it passes the top of the gear. Disconnect the cable from the derailleur, check cables for unusual/excess friction, check all cable-ends and ferrules, refit and reset the indexing.
The fact that your troubles started with the damaged hanger gives good odds that it's related. It's no guarantee, but I wouldn't start swapping components just set...
What use is a philosopher who doesn't hurt anybody's feelings? -
Having the fault show itself after a wreck would lead me to think the wreck is the cause. When changing the derailer hanger, look carefully at the derailer when it's off the bike. Over the years, I've broken 3 different derailers on the 'mount side'. On the back side of the securing bolt, there's a shaped metal 'plate' that is secured using a 'c' clip. This metal plate also houses the screw adjustment (the lone screw on the backside, not the limit screws) that aligns the derailer with the vertical drops. This 'plate' to which I refer is the part I've broken on all 3 occasions.
After the break, I was able to adjust the derailer on the stand to perfection. It wasn't until I got on the bike and applied load that the ghost-shifting would become apparent. It was very frustrating the first time I broke one as I didn't realize it was broken (can't really be seen unless the derailer is off the bike) and all signs on the repair stand were that things were good. Needless to say, the problem was eventually found and resolved.
Incidentally; after doing this to 3 different derailers and dropping coin each time, I nixed the derailer all together. I now ride a Rohloff and will NEVER put a derailer back on any of my mountain bikes.
Thanks for all the excellent suggestions and insight, guys. I'll definitely look into each of your suggestions further ASAP.
I verified the chain length is correct and 'B' screw is adjusted properly. I also removed, cleaned, re-lubed, and reinstalled both the derailleur cable and chain and took the bike for another ride - the original problem has improved a good bit, now just a couple slow shifts and one ghost shift during an hour ride. But a related problem is now more obvious - the bike is shifting 'harder' than it should, especially when downshifting two gears at a time - it really clunks hard when the chain moves over and causes a very noticeable 'skip' through the drivetrain when pressure is being applied to the pedals during the downshift. It's not as bad when upshifting and also seems a good bit worse in the middle gears (4-5-6), which are the ones I use most. Figuring this might indicate a problem w/the cassette, I took a good look at it and found a lot more teeth on those gears are slightly chipped/rounded looking than the other gears - nothing that appears to be major, but I wonder if it's enough wear to be causing shifting problems.
I have another rear wheel I can swap out w/nearly new XT cassette, which should better determine if the cassette is the major contributor, at least to the clunking issue.
I'll follow up after a bit more checking/swapping parts, etc.