Need more rear derailluer clearance with cassette/chain
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  1. #1
    bas
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    Need more rear derailluer clearance with cassette/chain

    background: shimano ultegra triple, 52/42/30, rear 12-27 ultegra, trek 5.2

    I put on a 27 tooth rear from a 25 a few weeks ago...I didn't have any serious problems, everything was tuned right.

    On a sponsored ride Sunday, front derailluer would only shift while in the middle gears.
    I had one donkey adjust my front derailluer on a ride - and said my problem was the screw was stripped and he got it work by removing the pinch down washer and using the bolt to hold the cable in.. fine.. but he earned donkey statyus because he left the inner stop screw on the rear all the way almost all the way out (my rear derailluer was rubbing against my spoke!! and completely misaligned in other gears).
    He also lowered the front derailluer back in line with the chain (I had it maxed out at the top to try to prevent the chain from rubbing in the big gear on the harder gears).

    I had another mechanic correct the rear derailluer on that bike ride at the next stop..

    I did some readjusting on front derailluer, and on the rear last night.

    I've got the stop hanger screw all the way-and could use a little bit more distance to keep the chain/derailluer/cassette from clicking when in the 30-27.

    I either need 1) a longer screw (which would probably end up not ending on the stop) or

    2) I need to know if I undo the bolt holding in the rear derailluer - can I adjust the position of the rear derailluer, and then use be able use less/more screw to give me some more
    room when i'm in the 30-27?

    I've never put one on - I can only assume it would work like this. Can anyone explain this to me?

    Thanks.

  2. #2
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    A little clarity?

    Quote Originally Posted by bas
    front derailluer would only shift while in the middle gears. I had one donkey adjust my front derailluer on a ride - and said my problem was the screw was stripped and he got it work by removing the pinch down washer and using the bolt to hold the cable in.. fine.. but he earned donkey statyus because he left the inner stop screw on the rear all the way almost all the way out (my rear derailluer was rubbing against my spoke!! and completely misaligned in other gears). He also lowered the front derailluer back in line with the chain (I had it maxed out at the top to try to prevent the chain from rubbing in the big gear on the harder gears).
    I'm going to guess here that the problem was that the cable clamp bolt had stripped the derailleur threads - is that right? Why would that cause the problem you describe, which I think is that the only time the FD would shift was when you were in the middle cogs on the cassette - is that correct? Why did he adjust the rear derailleur when the problem was front shifting? He did the right thing by lowering the FD - perhaps he should have rotated it a bit as well. Raising the FD is not the way to prevent chain rub, but it can significantly reduce FD performance.

    Quote Originally Posted by bas
    I had another mechanic correct the rear derailluer on that bike ride at the next stop. I did some readjusting on front derailluer, and on the rear last night. I've got the stop hanger screw all the way-and could use a little bit more distance to keep the chain/derailluer/cassette from clicking when in the 30-27.
    Huh? If you know how to work on the bike yourself, why are you having mechanics mess about in the most disadvantageus situation - in the middle of an organized century ride? What do you mean by "stop hanger screw all the way"? Front derailleur, rear derailleur, upper limit screw, lower limit screw, "b" screw, all the way in, all the way out? Please explain "could use a little bit more distance to keep the chain/derailluer/cassette from clicking when in the 30-27." What is clicking on what? Chain rub on the FD cage, RD cage hitting the spokes, RD upper pulley not centered on the 27t cog, upper pully too close to the 27?

    Quote Originally Posted by bas
    I either need 1) a longer screw (which would probably end up not ending on the stop) or

    2) I need to know if I undo the bolt holding in the rear derailluer - can I adjust the position of the rear derailluer, and then use be able use less/more screw to give me some more
    room when i'm in the 30-27?

    I've never put one on - I can only assume it would work like this. Can anyone explain this to me?
    Please explain "probably end up not ending on the stop." Are you suggesting putting in a longer limit screw, and are you then worried that it wouldn't line up with the stop on the derailleru body? Again, FD or RD? Or are you talking about the "b" screw that adjusts the angle of the RD body?

    The RD is already free to pivot about the bolt that goes into the frame, and probably has a spring in there to make it all work properly. You can tell this by moving the RD - you will see that it will pivot, so there's no point in removing the mounting bolt.

    I would strongly suggest that you take this to a bike shop or a knowledgeable rider. Hopefully they can not only fix it for you, but can explain what they've done and how things work. You probably can find a longer bolt for the FD cable clamp, but you might want to consider drilling it out and installing a helicoil.

  3. #3
    bas
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    Quote Originally Posted by Kerry Irons
    I'm going to guess here that the problem was that the cable clamp bolt had stripped the derailleur threads - is that right? Why would that cause the problem you describe, which I think is that the only time the FD would shift was when you were in the middle cogs on the cassette - is that correct? Why did he adjust the rear derailleur when the problem was front shifting? He did the right thing by lowering the FD - perhaps he should have rotated it a bit as well. Raising the FD is not the way to prevent chain rub, but it can significantly reduce FD performance.
    I went and got my food/drink - I don't know why he touched the RD.


    Huh? If you know how to work on the bike yourself, why are you having mechanics mess about in the most disadvantageus situation - in the middle of an organized century ride? What do you mean by "stop hanger screw all the way"? Front derailleur, rear derailleur, upper limit screw, lower limit screw, "b" screw, all the way in, all the way out? Please explain "could use a little bit more distance to keep the chain/derailluer/cassette from clicking when in the 30-27." What is clicking on what? Chain rub on the FD cage, RD cage hitting the spokes, RD upper pulley not centered on the 27t cog, upper pully too close to the 27?
    I didn't want to deal with not being able to shift the FD. I didn't have a work stand to work on and didn't want to worry about it.

    The RD screw that does the hangar adjustment is all the way in. It doesn't look lined up either. When in 30x27, the RD pulley is to close to the 27 tooth cassette, and clicks. If it is tighter - it will click all the time.


    Please explain "probably end up not ending on the stop." Are you suggesting putting in a longer limit screw, and are you then worried that it wouldn't line up with the stop on the derailleru body? Again, FD or RD? Or are you talking about the "b" screw that adjusts the angle of the RD body?
    The RD is what I'm talking about. Yes, the b screw. My question is if I take off the RD, and re-bolt it on - can I adjust the position of it so I can set the b screw to a more normal position than all the way in.


    The RD is already free to pivot about the bolt that goes into the frame, and probably has a spring in there to make it all work properly. You can tell this by moving the RD - you will see that it will pivot, so there's no point in removing the mounting bolt.
    Yes, it has a spring. I was thinking I could turn it clockwise some.

    I would strongly suggest that you take this to a bike shop or a knowledgeable rider. Hopefully they can not only fix it for you, but can explain what they've done and how things work. You probably can find a longer bolt for the FD cable clamp, but you might want to consider drilling it out and installing a helicoil.
    Its only $45 for a new triple ultegra FD, so I'll just replace it.

    ALso - another thing that might be causing the RD to be out of wack - is that I just noticed a little wobble in the rear wheel wheel.

    So my course of action will be to first true the rear wheel, then dish it ( when I true wheels, the dish always go out of wack). The dish looks ok right now by eyeing the rim in the brake pads - but my dish tool will point out problems.

    I bet this might get the RD pulley off the cassette and give me some more room.

  4. #4
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    It sounds like somebody tightened up the "B" screw without relieving the tension on the rear derailleur. This can bend the derailleur, hanger, and the screw.

    The option remains to put the "B" screw in backwards so that the head is touching the hanger. In the usual Ultegra GS, this is the setting for using a 30t to 32t rear gear and should certainly give a 27t enough clearance.

    Perhaps the problem is more simple.

    You could just go and get a nice new Dura-Ace chain (very strong, less friction). The resulting installation will inherently cause it to be sized to fit your 27t gear. This is probably about 112 links.

    The new installation (because of your larger cassette) will make for a slightly longer chain and possibly less chance of going "bumpity" on the largest rear cog. Whether or not that helps at all, that particular chain makes a lot less noise. And, a new chain is perhaps indicated if many derailleur adjustments have not yet worked.

    EDIT: If you need more room in the front derailleur than is called for by the standard installation, then there's a good chance that your bottom bracket is worn out or simply loose. You might check it before fighting with the front derailleur further.
    Last edited by danielhaden; 08-30-2006 at 07:20 AM.

  5. #5
    bas
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    It sounds like somebody tightened up the "B" screw without relieving the tension on the rear derailleur. This can bend the derailleur, hanger, and the screw.
    me?? ;)

    The option remains to put the "B" screw in backwards so that the head is touching the hanger.
    Thats a unique idea!

    In the usual Ultegra GS, this is the setting for using a 30t to 32t rear gear and should certainly give a 27t enough clearance.

    Perhaps the problem is more simple.

    You could just go and get a nice new Dura-Ace chain (very strong, less friction). The resulting installation will inherently cause it to be sized to fit your 27t gear. This is probably about 112 links.
    Yes - I already have a DuraAce chain on. I remember chopping off 8 links. My "break it-fix it -ride it" cd said to measure inner front to outer rear (which is the same) as before (12-27, 12-25) with the 30 tooth inner front ring.. 30x12.. No mention was made to measure the other way - 52x27.. (this setting is fine too, the RD is pulled off the cassette with good clearance).

    The new installation (because of your larger cassette) will make for a slightly longer chain and possibly less chance of going "bumpity" on the largest rear cog. Whether or not that helps at all, that particular chain makes a lot less noise. And, a new chain is perhaps indicated if many derailleur adjustments have not yet worked.
    If I move the RD by hand - I can get the extra clearance. I'll take photos before I true/dish the rear wheel which maybe out of whack causing the rear cassette to get too close.

    Thanks for the information

  6. #6
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    You might check and make sure that when your chain is around both the biggest rear sprocket and biggest front chainring that the rear derailleur looks stretched out. It should.
    Then check the smallest rear cog and smallest front chainring to see that the derailleur does not fold so far that the chain touches itself.
    It should not.
    In fact, it should be able to downshift from the small-small combination with reliable indexing. If it can't then the chain is about an inch too long.
    Tip: Never break the chain in the same place twice (Don't punch out a chain-patch pin).

    And there's a bit of tolerance in that stuff above.

    Rear cassette getting too close? Neuvation wheels? The hubs they use lack a bit of space. Just a guess there. ;)

    You might also go to the bike shop and have them use the usual rear derailleur hanger measurement device. It is very common for derailleur hangers to get slightly bent.

    Well, since the hanger is only about $6, you could just get a new rear derailleur hanger. ;) This alignment necessity is very frequent for 9 and 10 speed systems.

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