Chain rubbing on front derailleur

[benb]

OK, I recently replaced the whole drive train - crankset, cassette, and chain. I readjusted the gears, and most of the time it's all fine - smooth and almost silent.

I know that if I use small-small or big-big I will get chain rub, but I am getting some rub when I'm in the middle ring. I would think that you ought to be able to use any gear on the cassette when in the middle ring without it rubbing. It's rubbing in the lowest 3 gears, so I suspect I need to tweak the front mech.

Can someone advise on the best method to adjust the mech to minimise this problem?

Thanks.

 

[PpPete]

I avoid the outer sprockets on the cassette when in the middle ring.
Some shifters have a half-click that you can use to "trim" the position of the front mech cage without actually changing gear.
Otherwise give the cable adjuster on the front mech cable a tweak. As you are rubbing in lowest gears (biggest sprocket on cassette) you want a slightly tighter cable - so anti-clockwise on the adjuster. Halt turn at a time, until you eliminate the rub in as many gears as possible.

 

[benb]

I avoid the outer sprockets on the cassette when in the middle ring.
Some shifters have a half-click that you can use to "trim" the position of the front mech cage without actually changing gear.
Otherwise give the cable adjuster on the front mech cable a tweak. As you are rubbing in lowest gears (biggest sprocket on cassette) you want a slightly tighter cable - so anti-clockwise on the adjuster. Halt turn at a time, until you eliminate the rub in as many gears as possible.

Thanks, I'll give that a go. I was thinking I'd have to keep playing with the min and max adjustment screw on the mech itself.

 

[subaqua]

Thanks, I'll give that a go. I was thinking I'd have to keep playing with the min and max adjustment screw on the mech itself.

unless ther chain is coming off the rings at the top and the bottom of the Front mech travel there is no need to adjust the limit screws. its cable tension thats the issue and after fiddling for 3 hours and getting nowhere adjusting limit screws i succumbed and did what i should have done . RTFM . 30 minutes later 2 properly adjusted mechanisms (front and rear) and the mystery of indexed gears gone forever and silky smooth changing .

techdocs.shimano.com is a great source of info and the SRAM website has a full tech manual available for down load with troubleshooting guides too.

 

[Cubist]

^^^^ Wot 'e said ^^^^

 

[RecordAceFromNew]

If the front mech is rubbing when at the 3 largest sprockets at the back when on the middle chainring, then the front mech is too far outboard in comparison with the chainset. That means the front mech cable is too highly tensioned (because the mech spring defaults inboard), so you need to turn the cable adjuster clockwise reducing cable tension. I would simply do it by sight first off, adjusting the cable tension so that the front mech is dead centred on the middle ring.

In your case there is a possibility that there is a chainline issue, given you updated the drivetrain. That could happen if the chainset/bb are not replaced like with like, but hopefully that is not the problem.