I recently dismantled my bike for a service a couple of days ago and am having problems with the rebuild. After rebuilding the front and rear derailleur I noticed that the front gears will change from the smallest cog to the largest, but not largest to smallest. Both screws have been adjusted so that the chain is clear, but I am still having no luck.
Is the cord too loose? Ive pulled it tight and fastened it in both high and low gears to no avail.
Light Makes Right
My guess is that it's slightly too tight actually. When on the small ring is the dérailleur against the stop or being held off of it by the cable? If it's on the stop you probably need to put a touch more slack on the limit screw.
Do you have an adjuster in the system? If not you might want to consider adding one. What sort of shifters are you running?
Im running on grip shifts. When on the smallest ring the cable is slack and the chain is just missing the stop. Once I shift up the cable tightens and pulls the chain onto the next gear. But then when trying to change down the cable just slackens and the chain stays where it is.
check to make sure the cable isn't getting hung up anywhere.
also the housing may be getting sucked up into a tight spot, check the housing and try taking the cable out of the spot where it goes into the derailleur and pull it tight with your hand while shifting it
Go to the Park Tool website. Follow their step-by-step instructions starting at the very beginning with the position of the derailleur on the seat tube. Without having the opportunity to see your bike, my guess is that the angle of the derailleur relative to the chainrings isn't right.