Adjusting front derailleur

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Adjusting front derailleur

Postby peter » Sat Aug 02, 2008 2:44 pm

Went out for a ride just now but half way through the front derailleur played up, the chain suddenly dropped to the small ring (it's a compact). I put the chain back to the large ring but it would just drop back to the small ring once I start riding.

Is it easy to rectify the problem? I would like to avoid a trip to the LBS if it's a simple fix. Any guidance would be appreciated.
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by BNA » Sat Aug 02, 2008 3:39 pm

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Postby U2adam!!! » Sat Aug 02, 2008 3:39 pm

There is a video on www dot bicycletutor dot com. I can't post a link because I am still a noob but it's on the 4th page of their vids.

This will give you something to watch while you are waiting for a decent reply from someone who has some experience with the adjustment i.e. not me.

Tim
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Postby zoom bean » Sat Aug 02, 2008 4:39 pm

Simple fix that usually works for me:

- Shift to your lowest gear (smallest sprocket up front, largest at the rear)
- Undo the bolt holding the cable in
- Now the cable should be loose, pull it tight & re-tighten the bolt
- Shift through all your gears and make sure it is working okay

If the derailleur rubs on the chain in certain gears use the adjustment screws to correct (the two screws side by side on top of the derailleur). On mine the screw closest to the chain adjusts the derailleur when it's in the largest gear. The screw closest to the seat tube adjusts the derailleur in the smallest gear. I understand that these can vary though, so it may not be the same for your bike.
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Postby Hawkeye » Sat Aug 02, 2008 6:15 pm

zoom bean wrote:- Shift to your lowest gear (smallest sprocket up front, largest at the rear)

Hey zoomer I hope you don't mind me correcting you on this... This only works at the rear on a low-normal RD. My Jekyll has a low-normal (aka Rapid Rise) RD, so that the cable is at its slackest when in the largest rear sprocket as yo usay.

However, my commuter has the much more common high-normal rear derailleur. In ths case you want the RD in the smallest sprocket with the cable slack. (In fact you have no choice - the cable is under tension in all the other gears).

Setting up the RD (assumes high normal):
Shift to smallest sprocket. Slacken off the cable tension adjuster knob (where the cable outer butts up against the shifter). Undo the cable retention bolt at the rear derailleur.

Use the H end-point screw to adjust so the closest jockey wheel is straight under the sprocket, then pull the cable tight and tighten the cable retention bolt.

Adjust cable tension with the cable tension adjuster knob as required to ensure clean shifting.

Important: Use the L end-point screw to ensure your chain doesn't climb off the biggest sprocket and into your spokes. :shock:

Setting up FD:
For the FD, a similar process applies.
Shift to little gear. Slacken fully the cable tension adjuster at shifter. Loosen off cable retention bolt at DR.

Make sure first of all that the outside edge of the cage is parallel to the big chainring. Then use the L end-point screw to adjust so that the cage is centred over the little chainring. Pull your cable tight and then tighten the cable retention bolt (ie, on the derailleur).

If the cage rubs or doesn't shift cleanly, tighten or loosen as required by using the tension adjustment knob where the cable outer enters the shifter. You will probably find that you need to add a little tension anyway to take up the slack in the cable from not being able to put quite enough tension on it before tightening the bolt.

Use the H end-point screw to ensure you don't over-shift too far and drop the chain off the outside of the big ring.

The H and L screws on either DR are only for setting the high and low end-points. If your cage rubs on the big chainring and you have previously set the end points so that it shouldn't, it's often because you have too much left slack in your cable in the little ring. It si possible to add too muchtension too, so just use your common sense and all should be fine.

Sorry about the novel. I hope this helps.
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Postby zoom bean » Sat Aug 02, 2008 7:07 pm

j.r.hawkins wrote:
zoom bean wrote:- Shift to your lowest gear (smallest sprocket up front, largest at the rear)

Hey zoomer I hope you don't mind me correcting you on this... This only works at the rear on a low-normal RD. My Jekyll has a low-normal (aka Rapid Rise) RD, so that the cable is at its slackest when in the largest rear sprocket as yo usay.

However, my commuter has the much more common high-normal rear derailleur. In ths case you want the RD in the smallest sprocket with the cable slack. (In fact you have no choice - the cable is under tension in all the other gears).

No worries, correct away for sure. I was assuming peter would only be adjusting the front derailleur that's why I mentioned that.

But yeah as you mentioned, you can't adjust most normal rear derailleurs in that gear.
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Postby Aushiker » Sat Aug 02, 2008 7:09 pm

U2adam!!! wrote:There is a video on www dot bicycletutor dot com. I can't post a link because I am still a noob but it's on the 4th page of their vids.


Have it linked here. I like the Bicycle Tutor's work.

Andrew
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Postby peter » Sun Aug 03, 2008 11:09 am

Thanks for the pointers guys. Oh boy this thing requires lots of patience, after 2 hours last night and an hour this morning, finally the shifting is working, but now the chain rubs the cage at the lowest and highest. May be the trip to the LBS can't be avoided.
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Postby Kalgrm » Sun Aug 03, 2008 11:39 am

peter wrote:.... but now the chain rubs the cage at the lowest and highest.

This could be as simple as adjusting the limiting screws, but I'll reserve judgement until you answer another question:

"Lowest and highest" is referring to which gear combinations? Do you mean small chainring and largest rear cog as "lowest" and large chainring and smallest rear cog as "highest"? If so, it's the limiting screws on the FD needing a slight tweak.

If you mean small chainring and smallest rear cog and/or large chainring and largest rear cog, you're using the gears outside their design parameters and you need to change the way you are using the gears. That's called "cross-chaining" and it's generally considered unwise to ride in those combinations for any length of time. It wears out the drive train more quickly.

Cheers,
Graeme
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Postby peter » Sun Aug 03, 2008 3:17 pm

Kalgrm wrote:"Lowest and highest" is referring to which gear combinations? Do you mean small chainring and largest rear cog as "lowest" and large chainring and smallest rear cog as "highest"? If so, it's the limiting screws on the FD needing a slight tweak.


Thanks Graeme, that's what I meant. Is the cage supposed to move a lot by turning those screws? The one on my bike moves very little, it went from rubbing to touching, so it has definitely made some improvement but the problem not completely gone.

I downloaded the Shimano service manual but it doesn't say anything new.
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Postby Kalgrm » Sun Aug 03, 2008 7:41 pm

Okay, well if you've backed it out and the FD still rubs the chain, you still have too much tension in the cable. Try this sequence:

0.5/ confirm your FD is parallel to your chainring. I'm assuming it is.
1/ put the chain onto the largest rear cog and the FD on the small chainring
2/ undo the cable clamp holding the cable onto the FD and wind the cable housing adjustment nut so that it is nearly all the way into the housing (it may be an in-line adjuster - if so, wind it in likewise)
3/ adjust the limit screw marked "L" until the FD just misses the left had side of the chain as you rotate the cranks (some frames flex a bit and you might need to back it out a fraction more to allow for this flex)
4/ pull the cable by hand through the clamp so that it the cable has no slack and tighten the cable clamp
5/ using the gear levers, change to the big chain ring and the smallest rear cog. The "H" limit screw should be adjusted so that you can't push the chain off the big chain ring
6/ wind out the cable housing adjuster nut with your fingers until the chain no longer rubs on the right hand side of the chain.

If it's still rubbing after doing that, it may mean your FD is not parallel to the chain rings.

It's a very simple thing to get right once you know the sequence of events to follow - not rocket science at all .... :)

Cheers,
Graeme
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Postby peter » Sun Aug 03, 2008 10:19 pm

Thanks for your step by step instructions, I will give it a go and see what happens.

Is cable housing adjuster nut the thingy just outside the shifter (outer casing adjustment barrel as Shimano calls it)?
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Postby Kalgrm » Sun Aug 03, 2008 10:41 pm

peter wrote:Is cable housing adjuster nut the thingy just outside the shifter (outer casing adjustment barrel as Shimano calls it)?

Yep.
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