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Old 10-11-08, 06:26 AM   #1
Shoegazer
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Front derailleur height problem with new chainring

I just replaced my Truativ Giga X Pipe Triple chainring with a FSA Gossamer triple. The X-Pipe large ring had 52 teeth and the FSA one has 53. The problem I am having is that the curve of the derailleur cage doesn't line up with the curve of the chainring. If I adjust the height so that the back of the cage clears the front chainring by 1mm, the front of the cage is a good 7mm over the chainring. The result is that I can shift from the large chainring to the middle one since the cage isn't making good contact with the chain. The derailleur is an Ultegra braze-on and I can see any way to adjust the angle of the cage. Any ideas on how I can fix this?
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Old 10-11-08, 06:44 AM   #2
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The difference between 52 and 53 is not great enough to cause this sort of problem. What kind of derailleur is it? Got any pics?

Normally, height over chain rings is set at the front. You are describing the sort of curvature that would be found on an MTB derailleur or one made for much smaller chain rings????
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Old 10-11-08, 06:48 AM   #3
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I agree with maddmaxx, the radius difference between a 52 and 53T chainring is not enough to cause the problem you are describing. Something else changed. Did you remove the fd and replace it out-of-line on the braze-on fitting or braze-on adapter clamp?
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Old 10-11-08, 08:09 AM   #4
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Here is a picture (I hope this works):



This is as low as the cage will go and still clear the large chainring when shifting.

Also, the front derailleur is the one that came with the bike and I have not touched the part where it attaches to the frame.
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Old 10-11-08, 08:23 AM   #5
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My first impression would be to adjust the tail of the cage to just clear the large ring during shifting (so it doesn't bind up). Start with the rear of the cage just a little "towed in" from parallell with the chain rings. Given that nothing has changed, I would assume that your derailleur setup worked in a similar position on the old crankset. It is possible that your shifting problems are the result of the cable tension and limit stops rather than the cage height. It may be that your "chain line" is slightly different with the new crankset requiring new derailleur adjustments.
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Old 10-11-08, 08:42 AM   #6
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I'll probably get scoffed at for this answer, but if it were mine, I would probably "cold set" the cage-judiciously, mind you- to a better functioning angle.
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Old 10-11-08, 08:44 AM   #7
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What is the middle chainring size?

Last edited by operator; 10-11-08 at 08:55 AM.
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Old 10-11-08, 08:52 AM   #8
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The derailleur is already as low as it can go and still clear the largest chainring. I've already adjusted the cable tension and limit stops after re-adjusting the height. I'm not sure what you mean by "towed in" from parallel.

The middle chainring is 39t.

At this point I'm thinking about putting a washer under the lower bolt where it attaches to the frame to hopefully change the angle of this thing and get the front of the cage closer to the chainring.

Last edited by Shoegazer; 10-11-08 at 08:57 AM.
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Old 10-11-08, 08:53 AM   #9
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I'll probably get scoffed at for this answer, but if it were mine, I would probably "cold set" the cage-judiciously, mind you- to a better functioning angle.
The entire cage does not match the curvature of the chainring. The only thing you could possibly cold set to get that to fit would be the frame braze on. You'd have to twist it. I'm not sure that's a good idea, but it seems like the only real explanation if the OP is completely sure the old one didn't sit in the same position.
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Old 10-11-08, 08:54 AM   #10
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The derailleur is already as low as it can go and still clear the largest chainring. I've already adjusted the cable tension and limit stops after re-adjusting the height. I'm not sure what you mean by "towed in" from parallel.
Ignore that, height is independent of the limits/cable tension. Toeing in the derailleur isn't going to do anything.
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Old 10-11-08, 09:13 AM   #11
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Is that mount actually brazed on, or is it an adapter? The sheet of paper makes it hard to tell. If it's an adapter, you should be able to loosen it and rotate it clockwise (looking from the top), so the mount moves backwards. Because of the angles, moving the der backwards will increase the vertical spacing on the rear much more than on the front. Then realign and lower the der.
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Old 10-11-08, 11:03 AM   #12
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Originally Posted by Shoegazer View Post
At this point I'm thinking about putting a washer under the lower bolt where it attaches to the frame to hopefully change the angle of this thing and get the front of the cage closer to the chainring.
If the derailleur is now sitting properly in the braze-on fitting, then that's the approach I'd take too. Shim the bottom of the derailleur where it bolts to the braze-on tab to rotate the whole thing clockwise.

Again, I can't believe the problem wasn't present with the former 52T big chainring.
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Old 10-11-08, 11:46 AM   #13
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If the derailleur is now sitting properly in the braze-on fitting, then that's the approach I'd take too. Shim the bottom of the derailleur where it bolts to the braze-on tab to rotate the whole thing clockwise.

Again, I can't believe the problem wasn't present with the former 52T big chainring.
Actually, after taking another look I noticed that the braze-on part is at a 45 degree angle to the derailleur. I think it would work better if I wedge something over the height adjustment bolt instead, since the height adjustment bracket runs perpendicular to the cage.
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Old 10-11-08, 03:11 PM   #14
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Do you actually have a problem shifting?
Sometimes they can be way off and work fine.
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Old 10-11-08, 05:13 PM   #15
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Do you actually have a problem shifting?
Sometimes they can be way off and work fine.
The problem is that it won't shift from the large chainring to the middle one. At least most of the time. I went for a ride this afternoon and after around 35 miles it actually started to shift without me using my foot to nudge the chain. I'm assuming that bringing the front part of the cage closer to the big chainring will put more pressure on the chain when shifting and take care of the problem.
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Old 10-12-08, 04:40 AM   #16
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Yeah, that's a common problem with having the FD too high. It has to move a large amount and bend the chain a lot before it shifts. Shimano even has a bend in the cage so that it is in closer contact with the chain to move it sooner, but that's of no help if the FD is too high.

I agree with Hillrider, wedge something in between the FD and the braze-on bracket to rotate the nose down and the tail up.
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Old 10-12-08, 04:12 PM   #17
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Maybe it's just the camera angle, but the center of the crank does not line up with the center of the seat tube. Odd.
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