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  1. #1
    Senior Member Agent B's Avatar
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    Hi all, just wondering about I problem I have with my new Giant Reign 3 mountain bike. It has 27spd LX derailers, running on a 9spd Sram cassette and Race Face Evolve XC crankset. The problem I have hving is that the derailer keeps jumping off the inner chainring onto the BB. I know where everyone is going to start with the adjusting the cable tension and inner stop. These were not adjusted properly at first but I corrected this, and now if I spin fast while changing down it will jump off. Otherwise it seems to work ok. The derailer is adjusted to just clear the chain while I am in the biggest cog on the cassette and the smallest chainring. can anyone give me an idea of what to look for next ?
    Last edited by Agent B; 12-25-05 at 01:52 PM.

  2. #2
    Senior Member Retro Grouch's Avatar
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    I have two potential solutions.

    The first is the one that you don't want to hear but here it is anyway. Go to the Park Tool website and readjust your front derailleur starting at the very beginning with the position of the derailleur on the seat tube. Every adjustment that you make on a front derailleur affects all of the subsequent adjustments so it's important to start at the very beginning and make sure every step is done right before you progress onto the next step.

    If you've already done that then I'd suggest getting a "Jump Stop" or a "Third Eye Chain Watcher". Both are small components that will prevent your chain from jumping off of the inside of your smallest chainring.

  3. #3
    Senior Member Agent B's Avatar
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    Hi retro grouch,

    I have checked the derailer hieght and alignment(paralell) with the chainrings and all is perfect. Can you please tell me about these "Jump stop" or "third eye chain watcher"
    it is the first time I have heard of these, also where might I be able to get one of these, please bear in mind that I live in South Africa and non standard items are impossible to get unless I import it myself.

  4. #4
    My bike's better than me! neil0502's Avatar
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    Presuming that your inner (lower) limit screw is correctly set (again: the ParkTool site is in order)....

    The Third Eye Chain Watcher is this:

    http://www.rei.com/product/9610812.htm

  5. #5
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    Quote Originally Posted by neil0502
    The Third Eye Chain Watcher is this:
    http://www.rei.com/product/9610812.htm
    I'd save money by not wasting it on cheap transient solutions and go for the expensive but ultimate AJ's Frame Guard:

    http://www.cambriabike.com/shopexd.asp?id=14233

  6. #6
    Senior Member Agent B's Avatar
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    Quote Originally Posted by neil0502
    Presuming that your inner (lower) limit screw is correctly set (again: the ParkTool site is in order)....

    The Third Eye Chain Watcher is this:

    http://www.rei.com/product/9610812.htm

    What the hell is that? Never seen one before in my life. I am assuming that it fits onto the seat tube below the derailer, is that correct? forgive my stupid questions but I guess it is the best way to learn, but how does that keep the chain from coming off.

    Thanks
    Brendan

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    Senior Member Retro Grouch's Avatar
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    That's exactly what it is. It's a little plastic finger that extends toward the granny chainring and prevents the chain from jumping past the chainring. I've never known one to fail. The nice thing about the Third Eye is that it installs with a hose clamp so it will fit any size seat tube.

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    Quote Originally Posted by 2_i
    I'd save money by not wasting it on cheap transient solutions and go for the expensive but ultimate AJ's Frame Guard:

    http://www.cambriabike.com/shopexd.asp?id=14233
    So, instead of a $10, 10 gram Third Eye that installs easily and works extremely well, you recommend a $40, 52 gm device that requires major disassembly to install and doesn't work any better. Makes sense to me.

  9. #9
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    Another possible fix: spacers for the granny mounting bolts. You won't need much--maybe 0.5 mm or 1.0 mm should do the trick. These would be cheaper and a lot less trouble (and a whole lot lighter) than that Frame Guard thing.

    Assuming your fder is correctly positioned on the seat tube (proper height and angle), do the following:
    1. Shift to the lowest gear (granny chring, biggest cog).
    2. Disconnect the fder cable.
    3. Adjust the low limit screw so that the the cage is JUST clearing the chain plates. Make sure your chain clears the rear tire.
    4. Reconnect the fder cable.
    5. Shift to the highest gear (big chring, smallest cog).
    6. Adjust the high limit screw so that the cage is JUST clearing the chain plates.
    7. Play around with the drivetrain. Check fder shifting and cage rubbing in different conditions, especially when cross-chaining. (I mean, nobody ever crosschains, and I know YOU never would, but just in case, see how the fder behaves anyway.)
    - If it rubs against the middle chring when in the granny gear and crosschained a fair amount (say, to the 3rd-smallest or 2nd-smallest cog) consider spacers for the granny. Again, thin ones (0.5 or 1.0 mm) should do the trick. This will ease front downshifts anyway, and will likely prevent even occasional overshifts onto the bottom bracket shell.

    The other thing to consider: how often are you really in your lowest gear? If it's not very often, a TINY bit of chain rubbing in the lowest gear (between the chain and the inner plate of the fder) may be OK, especially if the alternative is overshifting during a long climb.

  10. #10
    ppc
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    Agent B,

    Don't spend any money on chain guards and other gizmos. These are devices that hide a malfunction in your derailleur setup, instead of correcting it. They're a patch on a wooden leg.

    What you need to do is figure out what the problem is. Assuming you have adjusted the derailleur how it's supposed to be, there are several other things that could be happening. Try checking this:

    - The BB spindle might be a bit too long or too short, and the derailleur doesn't quite work in its intended range, so two of the rings work good but the chain goes off the third. See if one of the stop screws is all the way out, "feel" if the derailleur has a hard time reaching one way or the other, forcing you to over-compensate in the adjustment.

    - Check that the derailleur cable feeds in the intended groove on the derailleur arm, and not at the other side of the screw (I know, it's dumb, but everybody does dumb things once in a while).

    - Check that the derailleur is as close as possible to the largest chainring when fully extended, *and* the collar is flat against the tube when you tighten it down. I had a front derailleur once that would sit a little crooked on the tube and wouldn't line up on its own, causing all sorts of grief. So now I almost tighten the collar, wiggle the deraiilleur up and down a bit to make sure it's installed flat, then tighten it fully.

    If everything seems right to you, you can also try this: when the derailleur kicks the chain up to the largest ring, it's mostly the front/top of the cage that moves the chain, and when the derailleur kicks the chain down to the granny ring, it's the back/bottom of the cage that tends to do the work. Therefore, you have the option of favoring one behaviour over the other by angling the derailleur right or left. In your case, you have "too much kick down" so to speak, so you can try to angle the derailleur counter-clockwise slightly (i.e. the back of the cage moves outboard slightly) and readjust the derailleur. You might find your ideal setting this way.

    You can also try to move the granny ring inboard a bit, with 0.1mm spacers.

    Finally, as a last resort, you can try to bend the cage slightly. For example, you might want to spread it a bit at the rear, so the right face has a longer travel to touch the chain and kick it down. Or you can try to bend the back of the cage so the left face is more outboard, to help it keep the chain in check on the granny ring. The cage isn't that fragile, it won't mind too much if you don't overdo it, but I'd avoid playing with that until there's no other option.

    Of course, it's entirely possible that your derailleur just doesn't want to live with your bike, and you might want to try other brand/models.

    Good luck.
    Last edited by ppc; 12-26-05 at 10:53 AM.

  11. #11
    Senior Member Agent B's Avatar
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    Hi Everyone,

    Thanks very much for the answers. The BB is the original one that Giant supplies with their bikes, the derailer has no problem reaching the smallest and biggest chainrings, and their is about 1mm clearance between the biggest chainring and derailer outer cage. I thought about what everyone was saying about spacing the granny inwards with spacers, but was worried about the possiblilty of the chain jumping in between the rings but thinking about it now I doubt that will happen. I will check the cable routing into the derailer later and see if the is correct. ahhhh I was wondering about maybe adjusting the derailer angle. I think tomorrow I will just pull everything off and re-install the derailer from scratch and see what happens, if this does not help then I will try the spacing of the granny ring.

    I will get back to you guys and let you know what happens.

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    The derailer is adjusted to just clear the chain while I am in the biggest cog on the cassette and the smallest chainring. can anyone give me an idea of what to look for next ?
    So the inner cage just clears it, correct? Just making sure. I had a bike do this once with the derailleur cage adjusted correctly according to Parktool. HOwever the BB spindle was too long and was causing an extreme chain angle.

    I know you said that yours is original, but something has changed to make this start happening.

  13. #13
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    Quote Originally Posted by HillRider
    So, instead of a $10, 10 gram Third Eye that installs easily and works extremely well, you recommend a $40, 52 gm device that requires major disassembly to install and doesn't work any better. Makes sense to me.
    Occasionally, when something really serious happens to the chain, it will get pushed under the "Jump Stop" or a similar device and, then, you really get a mess in your hands. The device will contribute to chain deformation. In addition, you somehow have to get the chain out, while on the road. You can be sure to get your hands covered in grease, unless you carry gloves for those occasions. Some will just choose to pull the chain out by force, messing it up more.

    In my experience, while the stop screw is important, the chain will jump sometimes anyway off the smallest ring, particularly when there is a considerable size difference between the small and middle. The AJ Guard eliminates the jumps period. The Guard requires no fine-tuning of any sort such as the 'Jump Stops'. When the chain actually tries to jump, the fine-tuning of the latter will get messed up. So, yes, I advocate spending the $40 and dedicating quality time to your bike.

  14. #14
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    Hi Agent B.,
    I make the Jump Stop chain guide, and among my customers have been top pros riding the best equipment set up by the best mechanics. You may very well be correct that you cannot obtain a front derailleur adjustment which will eliminate your chain drop problems. The front derailleur inner cage plate shape and position is optimized for upshifts, not for preventing inward derailments. Sometimes the bike and component configuration permits a front derailleur adjustment that works acceptably well most of the time. Sometimes not.

    The surest way to prevent inward derailments is to have an anti-derailment guide in place. Theoretically, the best guide would be a ring guide, attached directly to your crank, but on most bikes there simply isn't enough room for such a guide between the crank and the chainstay. The AJ's frame guard is a well-built frame-mounted version of a ring guide, and I have recommended it on several occasions as a good alternative to the Jump Stop. The chief difficulty with the AJ's guard (aside from price) is that many bikes simply won't accept it. You need to have a BB with a fixed cup flange, you need to have BB locking ring that can sacrifice sufficient threads of engagement to make room for the guide when the BB is moved over, and you need to have an inner chainring which has a compatible horizontal position, and the inner chainring must also be small enough. (I did not find a max chainring size listing on their site, but from the photos, it looks to me like the max would be around 24 - 26T.)

    Seat-tube mounted guides are lighter, cheaper, easier to install, have more lateral adjustability, and they work with any size inner ring, but being positioned at the top of the ring, they cannot prevent reverse derailments, like the AJ's can. There are principally three types of seat-tube mounted guides: the hollow plastic Chain Watcher, the solid plastic imitators of the Chain Watcher (Deda Dog Fang, Redline, and various nameless OEM guides) and my Jump Stop (www.n-gear.com). The Chain watcher is one of the lightest, it has a fairly large guide region, and its worm drive clamp will accommodate any tube size or shape in its range, but the hollow plastic tooth does not wear well, and its cam positioning system will sometimes put the tooth far enough forward that the chain can catch a tooth before it hits the guide, and then the chain just pushes aside the flexible tooth--as happened here: http://www.precisiontandems.com/tiptimingchain.htm Even so, judging from customer reviews of it at mtbr.com, apparently some people have found it quite satisfactory.

    The solid plastic tooth guides are more rigid and wear a little better, but they have the same cam-type adjustment system with the same drawback. However, if positioned such that the chain can catch a tooth, these guides generally rotate on the seat tube. Although this can be hard on frame paint, it does at least move the guide out of the way so that you can get the chain back up. The solid plastic guides also have the smallest guide face, so sometimes the chain can hop right over the top of the tooth. When that happens, the tooth basically just serves as a chain hanger to keep the chain from falling all the way down and getting stuck between the crank and frame.

    At 30 grams, the Jump Stop is the heaviest of these seat-tube mounted guides, it is mostly limited to standard tube sizes, and it also will not work with some rear suspension designs or bikes that have no space between the front derailleur and a frame weld. But for bikes that can accept the Jump Stop, it is very difficult for the chain to get past its large, rigid, stainless steel guide plate. (The Jump Stop, also, is reviewed at mtbr.com.)

    If your top priority is saving every gram, your best bet is one of the plastic guides. If robustly eliminating derailments is your top priority, your best options would be a crank-mounted ring guide (if you can find one) or the AJ's guard, or the Jump Stop--whichever works best with your bike. (I don't know about the availability of the other products in South Africa, but direct mail overseas is no problem for me.)

    Cheers,
    Nick
    N-Gear
    ngear@gvtc.com

  15. #15
    ctp
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    Quote Originally Posted by ppc
    Don't spend any money on chain guards and other gizmos. These are devices that hide a malfunction in your derailleur setup, instead of correcting it. They're a patch on a wooden leg.

    WHAT??!! Why spend all that time making something work right when you can just spend $10 and make the problem go away?



    Sorry - I couldn't resist

  16. #16
    ppc
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    Quote Originally Posted by ctp
    WHAT??!! Why spend all that time making something work right when you can just spend $10 and make the problem go away? Sorry - I couldn't resist
    Because zero dollars can make the problem go away I prefer not to spend my hard-earned cash on fixing things that are designed to work together in the first place.

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    Quote Originally Posted by ppc
    Because zero dollars can make the problem go away I prefer not to spend my hard-earned cash on fixing things that are designed to work together in the first place.
    It's zero dollars if your time and labor are worth zero, and if you actually get it working well enough that you never suffer equipment damage or sustain an injury from derailment. (I've heard lots of stories of both.)

    As for the parts being designed to work together, even Shimano has put extended mounting tabs on many of their small chainrings--the sole purpose of which is to reduce the chance of the chain jamming between the small chainring and BB shell after the chain derails. Shimano has also patented several guides integral with their front derailleurs, and occasionally attempted to produce them, but all of them involved logistical problems which were far more easily solved by having a separate guide unit.

    I do think the inner cage plates of front derailleurs have a remarkably good design these days, considering the many different chainring configurations they are expected to work with. But those plates are specifically designed for performing consistent and reliable upshifts. It is no indictment of their design that they are only accidentally semi-useful for preventing downshifts derailments because that function was not part of their design.

    I do agree that there are some products which mask or sometimes even worsen a problem which is better fixed some other way. If your chain isn't releasing cleanly because your chainring teeth are badly hooked, adding a bash plate to knock the chain loose is a poor solution because it doesn't work very well and the impacts tend to increase the hooking problem. But an anti-derailment guide does no damage, can often prevent damage, and can even improve front derailleur downshift performance (since the inner limit screw setting no longer has to be a compromise between safe and fast downshifts). I'm sure there used to be purists who resisted having guide ramps under their brake blocks for easing wheel insertions too (ramps being a "patch" for bad wheel insertion technique) but sometimes, an easier way of doing things is simply an improvement on the previous "proper" way.

    Nick
    N-Gear

  18. #18
    Senior Member Agent B's Avatar
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    Hi all,

    Sorry for the delay been lazy and bad weather, but yesterday I decided to redo the derailer. First of all lossened cable clamp and then derailer. adjusted derailer height and made parallel. Then I had a problem that the derailer would not reach the biggest chainring, I thought this was weird as it used to reach it. Anyway took crankset off and was checking chainline it is set at 49mm, then found out the inner faceplate on the derailer was catching on the middle chainring, therefore it would not reach biggest chainring. Lifted derailer to clear. and tested, same problem as before. Tried lifting derailer higher so that the flange on the outer faceplate missed the chain when it is on the middle chainring. would shift up perfectly but would not shift down from middle to smallest chainring decided to move derailer down so the where the flange tapers off caught the chain when it is on the middle chainring. So far this seems to have done the trick. I need to do more testing, but it was raining when I was doing all this and had just about enough. Also found out the Giants support bar on the rear suspension triangle gets in the way of me loosening and tightening the derailer cable clamp so I need to get a balljoint allen key for this now. when I have done all this once again I will let you know. I also found that it will be impossible to use the jump stop or third eye chain watcher, the AJ frame guard will possibly work, or I might have just enough room to place another ring just on the inside of the crankset to stop the chain from jumping as Screwloose suggested. Posted some picks so you can see what I mean.

    Brendan
    Attached Images Attached Images

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    Brendan,
    If you have detached the shifter cable, make sure it is re-attached correctly. There is a small metal tab on many shimano derailleurs that the cable has to go over. when the derailleur is closest to the seat tube, it seems that the cable should go on the other side of it, so you'll be tempted to clamp down the cable in the wrong spot. Your derailleur will still work, but not very well, often skipping the middle chainring when you downshift from the largest ring. I did this once!

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    Hi Brendan,
    If I'm seeing your pictures right, I take it the lower link that straddles the seat tube rises under a load, swinging up alongside the derailleur clamp. If so, that would preclude all seat-tube mounted chain guides that I know of, including mine. If you do need a guide, pretty much the only places left to mount one would be on the crank or the BB. The crank is the better place to mount if you have the room for it (unaffected by crank flex, no adjustment hassles, larger radius attachment, less chain abrasion) but I know it's hard to find an inner ring guide for most cranks.

    A low-tech alternative to the AJ's Guard that you might have locally is an old-style steel spoke protector, the sort made for thread-on freewheels. Freewheel threads and BB threads were about the same size, so I've seen where some people have successfully mounted them under the BB fixed cup flange in the same position as the AJ's guard. Those protectors came in a variety of diameters and dish-depths, so if you can find a shop that still has an assortment, perhaps one of those would be the right shape for your bike--or close enough it could be bent to fit. (I've also heard of cases of mounting modified spoke protectors to the crank, but I gather that required extensive modification.)

    Best of luck,
    Nick

  21. #21
    Senior Member Agent B's Avatar
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    Hi Screwloose,
    You are correct in that the lower link rises under load. That is why I said that I could not use the jump stop or similar devices. If I still have a problems, then I will make a inner plate guard that fits onto the chainring, as you said this is the better idea. It will be easy to make as well, all I need is to make design up in CAD and then I'll get it laser profiled in stainless steel, that should work well. I might just be a good idea just to do this anyway even if the derailer is working fine.

    the korn, being a technical person it is easy for me to work out where the cable is supposed to go and anyway, the bike mechanics had the cable attached to it already, so I think I'll be stupid if I installed it differently, but then again, how good are these mechanics. At work I am an Industrial Electrician and most of the time I am showing our trained mechanics how to fix something ?????

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