Bicycle Mechanics - Mystery shifting issue
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11-08-10, 06:36 PM
Okay, now we have the quill stem grease issue solved... a real problem for you expert mechanincs to advise me on.
I've had a BD Windsor Tourist since mid-July. Rode a fair bit for conditioning before leaving on a 3.5 week, ~1300 mile, bike tour on it. Throughout this period, my rear derailluer ghost or mystery shifts without warning - that is, it shifts on it's own. Also had some issues with front derailleur adjustments requiring multiple adjustments of the limit screws.
I've had 3 different LBS's look at it here in New Orleans and 1 while on tour. Their "fixes"/adjustments usually work for a couple weeks or 200 miles then the problems return. I've also adjusted the front DR's limit screws myself (still wants to jump over the small ring and jam the cranks at times). Last week, the chain jumped off the front and jammed in the cassette to the point where I almost had to take out a link to free it up.
Ideas? What might have the LBS mechs overlooked?
What can I, a tech-challenged person, try on my own?
I've probably got $1-150 invested in this particular problem already and really would prefer to not throw any more money away. The bike's not unrideable, just aggravating, right now.
11-08-10, 08:50 PM
If you haven't read this already, you might want to start here...it's an excellent reference on shifting issues and derailleur adjustments:
11-08-10, 09:52 PM
Yep.. first place I went.
Surprisingly to me, 4 different shops haven't been able to adjust things so they'll stay fixed longer than a couple weeks.
11-08-10, 11:17 PM
First, I'm no mechanic, but have built up a couple of bikes and am not afraid to install / adjust my own derailleurs.
If the adjustments work for a while and then start messing up, and since it's a relatively new bike, it almost sounds like either cable stretch or friction problem. Cables should be pre-stressed when installing, but by now they should be properly broken in. Another possibility is maybe the cable friction is increasing for some reason.
On the FD, the cage should be within 1-2 mm above the large chainring teeth...just enough to prevent the teeth from hitting the cage. Having it as low as possible helps control the chain better. (Adjusting cage height will alter the cable tension so you'd have to redo the clamping of the cable and limit screws.) When in the small front / large rear combo, the chain should almost be rubbing on the FD cage. Adjust the limit screw until it barely rubs, then back off a hair. Also you could play with the alignment of the cage, as far as being parallel to the chain rings. If the cage is not aligned just right, even adjusting the limit screw so the chain almost rubs may leave the front of the cage too far inward to prevent the chain from coming off. It takes some fiddling. The other thing is, when the chain falls off on the front are you cross chaining? That can make it more likely to come off.
You might also want to try a chain keeper to prevent the chain from coming off.
On the RD: did any of the mechanics check your RD hanger for alignment using an alignment tool? I had a brand new bike with a bent hanger, and it messed up the shifting. Also I have a bike where reinstalling the rear wheel always messes up the shifting, as it makes the RD hanger and cage flex inward by some amount depending on skewer clamping pressure. If it's nothing to do with hanger alignment, my guess is it could be a cable friction issue of some kind.
It might help if you would tell us what components are on the bike, number of rear cogs, and type of shifters especially.
11-09-10, 03:12 PM
jayp will have to take a look at that.
I assumed the LBS's have done so - especially as I returned to the same one 3 times for the same problem after their first adjustment didn't help. Both they and I got frustrated with each other after they wanted to continue to charge me for fixing/re-fixing the sme thing and I refused to pay more.
Anyway, thanks for the suggestion.
11-09-10, 03:45 PM
If the hanger alignment has been checked the obvious thing to do would be to temporarily try a different derailleur, especially if the bike was purchased used. The derailleur itself can be twisted so that it does not shift or hold a gear properly, though any decent mechanic should be able to see that by eye - typically when one pulls back on the derailleur body the pulley cage will not stay aligned in the same plane.
11-09-10, 06:48 PM
No available spare derailleur. Bike was purchased used from Bikes Direct.
11-09-10, 07:39 PM
This is going to go nowhere fast. You need to eliminate every single variable yourself or you will chase stuff down FOREVER.
1) Remove and at least inspect all cable and housing, for incorrectly finished ends or excessive friction
2) Better yet, remove and replace rear derailleur cable and housing YOURSELF, ensure it is clamped in the proper spot! (See relevant shimano techdoc if you need help)
3) Remover rear wheel, check cassette lockring tighteness. Make sure the stack is not loose on the freehub body.
4) Reseat rear wheel into the bike, and engage the QR with the BIKE ON THE GROUND
5) Grab rear derailleur hanger and see if it is loose
6) Check trueness of rear wheel
7) Align hanger
Once all this is all checked, proceed to doing your standard rear derailleur adjustment.
8) High limit
9) Low Limit
10) Pre-stress cable and housing
11) Tension adjustment
P.S Check that there are no loose frame cable stops and that the bottom bracket shell guide is also conforming to the shell properly and it is secured and the cable is routed correctly through it.
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