Another FD Adjustment Problem by a newbie
08-29-05, 12:01 AM
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Another FD Adjustment Problem by a newbie
I replaced the rusted derailler cables on the used vintage bike I bought. The RD readjusted OK: I just needed to reset the tension properly until it indexed precisely. The FD I had trouble with. (I have the Park Tool Blue Book)
I can shift to all 3 chain rings with almost none to minimal chain and cage rubbing on the worst chainline cog and chainring combinations so there is no chainline problem. The limits are set properly so the chain cannot fall off the small ring or get sucked off the big ring. The FD up shifts smoothly and rapidly. However in down shifting from the big ring to the middle ring, the chain drops to the small ring. Then I have to upshift to the middle ring. When I have it in the middle ring it down and up shifts OK.
(Oh, the outer cage clearance is one penny's width from the big ring and the cage and chain parallelism is not calipered but eyeballed as well as a newbie can.)
Is this behavior being caused by the tension being a tad too high (which can be tweaked with the barrel adjusters)? I know if I don't set the high limit properly, my shifter will index and drop the chain off the big ring, so my shifter has plenty of FD swing reserve (maybe too much?). Or is the problem that my shifter cams are worn and I need new levers or there is a tad too much tension or force on the cams? One can't observe the inner workings of the shift lever, only observe the amount of cable movement. I can remove the lever cover and examine the index cams and maybe modify their shape with a dremyl.
I had replace the BB cable guide because I was having cable and BB rubbing problems with another FD which routed the cable differently. This replacement guide seems to be not perfectly circumferentially flush with the BB. I wonder if it is flexing when the cable tension is being reduced in down shifting. I guess I should reinstall the original cable guide to remove this variable.
Would appreciate any comments.
Sinchi
I can shift to all 3 chain rings with almost none to minimal chain and cage rubbing on the worst chainline cog and chainring combinations so there is no chainline problem. The limits are set properly so the chain cannot fall off the small ring or get sucked off the big ring. The FD up shifts smoothly and rapidly. However in down shifting from the big ring to the middle ring, the chain drops to the small ring. Then I have to upshift to the middle ring. When I have it in the middle ring it down and up shifts OK.
(Oh, the outer cage clearance is one penny's width from the big ring and the cage and chain parallelism is not calipered but eyeballed as well as a newbie can.)
Is this behavior being caused by the tension being a tad too high (which can be tweaked with the barrel adjusters)? I know if I don't set the high limit properly, my shifter will index and drop the chain off the big ring, so my shifter has plenty of FD swing reserve (maybe too much?). Or is the problem that my shifter cams are worn and I need new levers or there is a tad too much tension or force on the cams? One can't observe the inner workings of the shift lever, only observe the amount of cable movement. I can remove the lever cover and examine the index cams and maybe modify their shape with a dremyl.
I had replace the BB cable guide because I was having cable and BB rubbing problems with another FD which routed the cable differently. This replacement guide seems to be not perfectly circumferentially flush with the BB. I wonder if it is flexing when the cable tension is being reduced in down shifting. I guess I should reinstall the original cable guide to remove this variable.
Would appreciate any comments.
Sinchi
