Chain Rubbing on front derailleur

[Truth]

Hi all,
Help , I am confused !
The chain is rubbing on the front dérailleur but only when in the smallest rear cog and when on the two largest front ones, if that makes sense.
I have tried adjusting the screws on the dérailleur , after watching how to adjust you tube videos , and frankly NEITHER screw seems to do anything at all. . . . . . . .
Any ideas?
Also will the rubbing damage the dérailleur and/or chain ?
Cheers

 

[gbb]

Avoid using small rear - large front or vice versa, it will cause excessive wear on the components, They simply can't cope with those combos, no-ones can.
Look from above when in those combos and you'll see the chain 'bending' ..its bad for it.

 

[Usehernamegood]

I was once told by a local bike mechanic that if you ride with the chain on the largest cog - you're doing it wrong.

 

[mrbikerboy73]

Large front and small rear cogs are fine. It's small front/small rear or large front/large rear combinations that you want to avoid.
Sounds like a little more tension on the cable is needed to move the front mech out wards. If this doesn't work then it's the limit screw that needs a tweak.

 

[Truth]

I spend half the time in the saddle in large front small rear so I hope you are right Mrbikerboy!
How do I change the tension on the cable please
Sorry , I haven't got a clue and as I say adjusting the 2 small derailleur screws did nothing at all for some reason?
Thanks for all of the replies

 

[Bazzer]

The screws should make an adjustment. On my old bike I wasn't convinced the screws were working until I screwed them IIRC anti clockwise, then found the mechanism wouldn't move, so I knew they were working.. So having found a way to stop the gear changing, I knew the opposite way would stop the rubbing.
I presume from your comment about the two biggest rings at the front, that you have a triple front. The gear change gate can be adjusted to stop rubbing when on the middle ring by the barrel adjusters on the gear cable. These will be fitting on the outside of the gear cable with a screw thread, which may or may not be visible. This might be just above the front mech or further up the frame where the cable outer stops at a lug. Alternatively if the front mech is a Shimano, and the levers are STI, the barrel adjuster mat be near the lever. Also I think there is a halfway movement of the gear/brake lever which can stop the rubbing, provided the cable tension isn't too loose.
I know you say you have looked at you tube videos, but in my experience the quality varies, even though they are telling you the same thing. Have look at at as many vids as you can find for a triple front (assuming that is what you have). If you have still having problems, or if your front mech doesn't accord with with what you are seeing in the vids, for example not having barrel adjusters, it could be visit to your LBS.

 

[si_c]

As @Bazzer says, with the derailleur there is often a barrel adjuster in the cable line somewhere on a road bike you can adjust to increase the cable tension which will push the deraiileur outwards slightly and hopefully stop the rubbing effect. If it doesn't you may need to adjust the limit screws (the one labelled H or high) to allow it to push out a bit more.

If you are on a mountain bike then there may well be a barrel adjusted on the shifter similar to the ones on your brakes. If not then take it to the LBS should take them a matter of moments to fix, but make sure they show you what they did so you know what to do next time.

 

[Nigelnaturist]

As @Bazzer says, somewhere along the gear cable there is a barrel adjuster, depending on the shifters, Tiagra/Sora/Claris can have one as the gear cable leaves the shifter, 105 and above its likely to be either inline somewhere or on the down tube where the down tube shifter would be, turn clockwise to tension, the screws on the mechs themselves are just stop adjusters, in other words stop the shifter moving to far so as the chain comes off, once set they very rarely need adjusting. If you hold the cage in one hand and adjust the screw you will feel the cage move, however only do it when on the large or small rings, with the shifter set to that position, and adjusting the appropriate screw, if nothing happens its likely to be the wrong screw. There is also a trim feature, where by you can press the lever in a little and will move the cage to the right, press the release paddle/thumb lever a little and moves slightly to the left, this is only on the front.

 

[Truth]

Thanks everyone
I should have said in the first place that I have got a Kona Dew Hybrid, its a triple change. The derailleur is Shimano, think the trigger gears are too
So there should be a barrel adjuster by the trigger then, similar to my brake ones? I think I have noticed that in fairness. I take it I adjust the left hand one that changes the triple front?
I don't understand how the two screws on the derailleur did nothing, no harm , no good? Weird.
Will the rubbing do any damage?

 

[Bazzer]

Damage? Well you have metal rubbing on metal that isn't supposed to except temporarily as you change gear.Why create a problem if it's fixable? Short term though I would say no, though it is also going to depend on your mileage in that term.
Personally that noise annoys the snot out of me, so when it happens, I will gradually get more cross and as a result damage something.

 

[derrick]

Not all bikes come with barrel adjusters, http://www.ebay.co.uk/itm/141485627507?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT
But they are really handy to have on the front derailleur, or you could just retention the cable.

 

[Truth]

Damage? Well you have metal rubbing on metal that isn't supposed to except temporarily as you change gear.Why create a problem if it's fixable? Short term though I would say no, though it is also going to depend on your mileage in that term.
Personally that noise annoys the snot out of me, so when it happens, I will gradually get more cross and as a result damage something.

Just gone into a dimly lit shed and turned the adjuster on the left hand trigger anti clockwise a quarter. SEEMS to have done the trick, when turning pedals backwards now I can't hear any scraping, although I will only know for sure tomorrow when I ride it!
Just hope me adjusting the derailleur screws won't cause any problems in the near future
Once again thanks for everyones time and advice

 

[si_c]

Just gone into a dimly lit shed and turned the adjuster on the left hand trigger anti clockwise a quarter. SEEMS to have done the trick, when turning pedals backwards now I can't hear any scraping, although I will only know for sure tomorrow when I ride it!
Just hope me adjusting the derailleur screws won't cause any problems in the near future
Once again thanks for everyones time and advice

Always feels good to fix things yourself

The screws on the derailleur are the limit screws, basically they are what stops you accidentally shifting the chain over the top and bottom of the chainrings at the front. If you were having a rubbing derailleur at the front it is likely that you won't have any problems with it there. The two screws are labelled L and H for low and high. If the chain drops off the cog when shifting onto the smallest gear then you need to adjust the screw labelled L and if you do it right you should see the deraiileur move almost imperceptibly away from the frame of the bike, and that should fix the problem.

If of course you have a problem with the chain falling off and wrapping around your crankarms and pedal you need to adjust the H screw. Here's a good explanation for adjusting the front derailleur.


View: https://www.youtube.com/watch?v=tfBiXgf8JxI

 

[Truth]

Thanks si_c ! I feel good about it until 7.50 when I ride it and realise I have buggared the gear settings up!
I will post later with an "idiots update"
Have a good day all

 

[Bazzer]

A quarter turn shouldn't have made that much difference other than to the rubbing, so it sounds as if those screws did actually work.