Front Derailleur Needs Constant Adjustment

[Rbz5416]

I bought a new 24 speed hybrid bike a couple of months ago. Very soon after picking it up I started having problems shifting from the middle to the largest chainring. Needed (what to me) seemed like excessive pressure on the thumb shifter to get it to engage. This got progressively worse until I was also having problems shifting down. The bike has been back to the retailer a couple of times now but the problem returns soon after. I've also had a go myself from the tech doc & got everything changing smoothly but 50 miles later, I'm again having problems.

Derailleur is a Shimano FD-M191, shifter is ST-EF51.

I'm struggling to understand what could cause the adjustment to go out so quickly & would be grateful for any suggestions.

The rear shifts cleanly & always has.

[DaveM]

Could be that the derailleur is not tightened to the frame properly and is slipping, could be the cable is slipping, could be the housing is not seating properly or is starting to slip through the little cups that catch the ends, could just be that the cable is stretching (as new cables usually do) and it will settle down once you get it adjusted again. Or it could be something else...
Sorry I can be more helpful without more specifics.

[Rbz5416]

(07-24-2012, 04:01 PM)DaveM Wrote:  Could be that the derailleur is not tightened to the frame properly and is slipping, could be the cable is slipping, could be the housing is not seating properly or is starting to slip through the little cups that catch the ends, could just be that the cable is stretching (as new cables usually do) and it will settle down once you get it adjusted again. Or it could be something else...
Sorry I can be more helpful without more specifics.

Thanks.

Derailleur seems solid as is still parallel to the chainrings & the vertical gap seems constant.

Cable clamp seems to do it's job.

Surely a new cable shouldn't stretch that much? As I said, the rear has shifted perfectly from day one with no adjustment.

Happy to provide any further information that may help diagnose.

[RobAR]

Dave steered you in the right direction. Like anything else manufactured in mass quantities by a machine, ferrules (the metal boot at each end of the cable housing) can pass QC inspection and fail in use. It is a $0.15 cent part, luckily. A missing ferrule will cause the same problem. Do you have black plastic ferrules? I don't trust them.
It may also be that a Brake Housing Ferrule was inadvertantly installed on your Drlr Cable Housing. They ARE different on better quality bikes. Brake cables are larger diameter than drlr cables.