Front Derailer keeps catching chain...worth replacing?

[Johnny5]

Hello,

I've had my Giant Defy 4 for over a month now, done over 250mi and loving it.

Anyway, I've set up my current front derailer (Shimano 2200) to as perfect as possible, there's no chain rubbing if I'm on the big chainset but if I'm on the smaller one, I get chain rubbing when I'm either on the largest or smallest ring on the back. It's really annoying me, I've adjusted the screws on the front derailer and I can either get the chain to not rub if it's on the biggest ring on the back in which the chain will rub if on the smallest ring and vise versa! Can anyone give me any suggestions on how to sort this problem? Will buying a new front derailer help? I was looking at a Shimano 105 front derailer, seen it for about £20, will it solve the problem? And is it just a straight swap and easy to fit?

Thanks for any help.

John.

 

[HLaB]

Its only done 250 miles, I would think it'd need replacing. Without seeing it hard to say but perhaps the angle and or height of the cage needs adjusted also? This guide might help but at 250 miles I think the shop would do it no problem you'd probably be better off there.

 

[Gerry Attrick]

Hold on. You should not use the small front ring with the smallest sprocket on the back as it puts too much strain on the chain. Adjust your limit screws so that you can use the small ring on the front with the biggest sprocket on the back without rubbing. Everything should then be fine.

 

[Johnny5]

Hold on. You should not use the small front ring with the smallest sprocket on the back as it puts too much strain on the chain. Adjust your limit screws so that you can use the small ring on the front with the biggest sprocket on the back without rubbing. Everything should then be fine.

Ok, thanks for that.

If it's too much strain for the chain when on the small chainset and smallest ring, then will there be any problems for the chain if on the largest chanset and largest ring?

 

[Johnny5]

Ok thanks. I'll just let the chain rubbing noise be a warning sound telling me that I'm in a gear which I shouldn't be.

 

[buggi]

yea, i thought this too when i first starting biking, i thought i needed a new derailluer but the shop told me you get that and you should never run the chain at extreme opposites, puts too much strain on it.

do i ever listen to this advice tho???

 

[jimboalee]

Firstly, make sure the front mech cage is properly aligned. That is, parallel with the chainrings.

You should make a chart of the ring/sprocket combinations and be able to see the progression of gears from low to high.
When you need to shift the chain onto the middle or large ring from the small ring, you will also need to shift the chain up onto a larger sprocket or two.

Machinehead's diagrams do the business.

The same applies when reducing ratio shifting the chain down to the small ring. You need to drop the chain onto a smaller sprocket at the same time. Flick both levers.

 

[peanut]

Firstly, make sure the front mech cage is properly aligned. That is, parallel with the chainrings.

.

its the front plate of the cage that needs to be parallel with the large chainring and approx 2-3mm above the teeth of the large chainring.
Your front mech cage may have received a knock out of alignment or if your chain has come off that can pull it out of alignment.

Cheap front mechs are not likely to be individualy checked for conformity . If the rubbing persists I would be tempted to slightly widen the gap of the front mech cage where it rubs by say 1-2 mm .

 

[HLaB]

Hold on. You should not use the small front ring with the smallest sprocket on the back as it puts too much strain on the chain. Adjust your limit screws so that you can use the small ring on the front with the biggest sprocket on the back without rubbing. Everything should then be fine.

Oops too much watching the Giro and not reading the full post, thats right the small-small combo and the large-large combo should be avoided anyway.

 

[jimboalee]

Cheap front mechs are not likely to be individualy checked for conformity . If the rubbing persists I would be tempted to slightly widen the gap of the front mech cage where it rubs by say 1-2 mm .

Mechanical tinkering. Sometimes this is the only way.

 

[jimboalee]

BTW, if that's a plated cage, be careful not to scratch or crack the plating.
The tin worm will get in.

 

[peanut]

Mechanical tinkering. Sometimes this is the only way.

absolutely or to put it another way a little bodging is better than a big hammer

 

[Johnny5]

I think widening the front derailed cage would help. What's the best way to approach this? How about adding a washer to the screw where it attached the front and back plate of the cage?

 

[peanut]

I think widening the front derailed cage would help. What's the best way to approach this? How about adding a washer to the screw where it attached the front and back plate of the cage?

That might work and is the simplest thing to try first but I expect the part where the chain rubs is probably near the middle of the cage in which case you'll need to widen it there.

Look closely at the inside faces of the cage and you should see whereabouts it is rubbing most. There is no formula for bodging ,despite what Jimbo may say (just kiddin Jimbo) its a case of careful jiggery and pokery .
Try to keep the front cage plate completly straight and gently bend the rear one out .

I would probably use my fingers and thumb but I've got arms like an Orangutan

It probably only needs about 1-2mm tops . Measure the cage width first by finding something that will wedge in the gap tightly then you can use that to measure the difference in adjustment.

 

[Mr Pig]

If the rubbing persists I would be tempted to slightly widen the gap of the front mech cage.

I have had to do that. The other thing that can help is to 'not' put the cage parallel. The chain sits at different heights in the cage depending on which gear s it's on. So by sitting the cage slightly twisted you can effectively make the cage wider! Further out and the top, further in at the bottom.

You shouldn't have to but sometimes it works. You really want to move the chain on the gears and look at exactly what is happening.