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Old 09-28-09, 07:48 AM   #1
lineinthewater
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B-tension screw fully tightened and derailleur still hitting cassette???

I'm confused. I installed a new 9-speed Shimano CS-6600 cassette 12/27 - my previous cassette was 12/26. With my previous cassette, the B-tension screw was fully tightened. I always thought that was weird there was no more room for adjustment away from the cassette - but it allowed the pulley to just clear so I didn't investigate further. Anyway, with the slightly larger 27 sprocket, it is now barely hitting and "clicking". Unfortunately, I didn't realize this until I put a hundred miles on it. I don't see any damage. Anyway, in an attempt to see if a longer B-tension bolt would actually get the pulley away from the sprocket, I put a test spacer in between the end of the bolt and the "claw" on the hanger. It seems to pull it away. Can anyone give me a sanity check here?? Now I'm really confused why the B-tension is fully tightened.
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Old 09-28-09, 07:52 AM   #2
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It sounds like your chain is too long. Try shifting to the big cog-big chainring combination and see if the rear derailleur still has a fair amount of slack. If so, resize the chain to just allow big-big and that should solve the problem.
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Old 09-28-09, 08:00 AM   #3
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If I understand you correctly, you asked me to try big chainring - big sprocket combo - which of course is a gear that would never be used. The rear derailleur is yanked way towards the front - definitely no slack there. BTW, when I installed the new cassette, I also installed a new chain. I measured it directly against the old chain - cut to same exact size.

Thinking along those lines, wouldn't a chain that is too tight prevent the B-tension from pulling away from the cassette? Maybe it's counter-intuitive, or it's too early for me???

Unfortunately, I was about to go out the door for a ride - definitely not happening until this is solved.

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Old 09-28-09, 08:20 AM   #4
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I recommended you see if the big-big combination still provided a significant amount of rear derailleur cage travel, not that you use this combination to ride in.

I'm surprised at your problem since all Shimano road derailleurs are rated to use a 27T cog and most, in real world use, will handle a 30T big cog.
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Old 09-28-09, 08:26 AM   #5
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I recommended you see if the big-big combination still provided a significant amount of rear derailleur cage travel, not that you use this combination to ride in.
Understood. "Significant amount of rear derailleur cage travel"? Can you be more specific? In this configuration, if you drew a line between the center of the pulleys, it would be roughly at a 45deg angle (towards the front of the bike) with the floor. I can still push the cage further essentially into a straight line parallel with the floor. Is that what you mean by "slack"?

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I'm surprised at your problem since all Shimano road derailleurs are rated to use a 27T cog and most, in real world use, will handle a 30T big cog.
It is an ultegra derailleur - it should be perfectly fine with 27T - like you say.

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Old 09-28-09, 08:41 AM   #6
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Running around with the B tension screw in will make the shifting, especially in the smaller cogs very sloppy and imprecise because now the chain gap (distance from bottom of cog to top of pulley) is too big. I agree it sounds like your chain is too long. You don't ride in big-big, but you don't want the drivetrain to lock up should you accidentally shift into it.
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Old 09-28-09, 08:50 AM   #7
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Running around with the B tension screw in will make the shifting, especially in the smaller cogs very sloppy and imprecise because now the chain gap (distance from bottom of cog to top of pulley) is too big.
The pulley is very close to the smaller cogs in those gears - I actually question if that is too close too.

I took a look at the pics on parktool's website:

http://www.parktool.com/repair/readhowto.asp?id=26

Scroll down to the pic that has the caption below: "Adequate chain length seen above in largest sprockets front and back. Note the chain bends at both pulleys." My derailleur looks similar to this in BIG-BIG, but the chain between the pullies is almost vertical. So my chain is a little longer than their pic configuration. But is that enough to be problem?

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Old 09-28-09, 08:57 AM   #8
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Well, chain length is usually done by putting the chain around the big cog and big sprocket and skipping the derailleurs. Pull the chain tight. The chain should overlap itself by 1 full link. Cut it there, then install it through the derailleurs.

I didn't quite understand your last post. If in the big-big, your lower pulley is closer to the front of the bike then the upper pulley, then that's about right. If the lower pulley is angled towards the back of the bike, then you've got way too much slack in the chain.

The other thing to check is if the b-tension screw is actually pushing against the hanger.
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Old 09-28-09, 09:02 AM   #9
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Originally Posted by lineinthewater View Post
The pulley is very close to the smaller cogs in those gears - I actually question if that is too close too.

I took a look at the pics on parktool's website:

http://www.parktool.com/repair/readhowto.asp?id=26

Scroll down to the pic that has the caption below: "Adequate chain length seen above in largest sprockets front and back. Note the chain bends at both pulleys." My derailleur looks similar to this in BIG-BIG, but the chain between the pullies is almost vertical. So my chain is a little longer than their pic configuration. But is that enough to be problem?
YES, your problem is too long a chain, as other posters have advised you. When you're at the limit of your derailleur as you are, chain length becomes the critical factor. Simply remove 1" of your chain, check your B screw for proper der pully clearance and go ride!
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Old 09-28-09, 09:15 AM   #10
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Well, chain length is usually done by putting the chain around the big cog and big sprocket and skipping the derailleurs. Pull the chain tight. The chain should overlap itself by 1 full link. Cut it there, then install it through the derailleurs.
Using this technique, the chain overlaps by five links. Hard to believe I've been using a chain so long for, well, so long.
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Old 09-28-09, 09:24 AM   #11
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I will not comment on chain length because some of that is your prefrence. But you can get other longer screws (however the angle starts getting wrong and you may need to bend the screws some to mate the frame stop correctly), and you can screw the one you have in from the back so the head rests on the frame. This usually gives a bit more.

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Old 09-28-09, 09:30 AM   #12
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Using this technique, the chain overlaps by five links. Hard to believe I've been using a chain so long for, well, so long.
FOUR links overlap, not five. My head is just not on straight this morn.
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Old 09-28-09, 09:51 AM   #13
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There is some confusion about the definition of a link. A link is only 1/2 inch. If you use the big/big method, you add 2 links or 1-inch to the length, after the ends are brought together. If the ends that come together are the same, they can't be joined and 3 links should be added.

I recommend the little/little method, particularly when you are using a cassette with the standard size largest-cog sold by Shimano for a road bike. With the chain installed through the RD it should be as long as possible in the little/little combo. If it's not hanging loose or rubbing the upper chain guide tab on the RD, it is not too long. When the ends of the chain are brought together, the lower pulley should swing down slightly, indicating that tension is being applied.

If your chain is really too long, it would hang loose in the little ring and several of the smallest cogs. If it never hangs loose or rubs the RD it is not too long.

There may be some difference in how a Shimano RD reacts to this situation, but with a Campy RD, the upper pulley just gets closer to the largest cog if you shorten the chain.

What is being overlooked here is that the RD hanger is not necessarily the same on all frames and neither is the stop that the B screw rests against. You may simply need a longer screw to compensate for an error in the frame.
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Old 09-28-09, 10:14 AM   #14
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OK, I took two links off (1 inch). I didn't want to risk taking any more off. The BIG-BIG combo looks exactly like the pic on parks website that I listed earlier. The SMALL-SMALL combo also looks exactly as prescribed in the pic next to their "Adequate chain length will not sag" caption - chain clears upper pulley by about an inch. The B-tension is still maxed out. Every gear *appears* to work (albeit the pulley is quite close), except for the lowest possible gear combo (little chainring, big cog). It is clicking and bumping on the rear derailleur (top pulley). The largest cassette cog is clearly passing within the frame of the pulleys. I get the feeling that, yeah, my chain might have been a tad bit longer than average, but something else is going on.

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Old 09-28-09, 10:25 AM   #15
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Some shimano road rear derailers are rated to only 26T. See techdocs.shimano.com for the specs on whichever model you have.
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Old 09-28-09, 10:27 AM   #16
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OK, I took two links off (1 inch). I didn't want to risk taking any more off. The BIG-BIG combo looks exactly like the pic on parks website that I listed earlier. The B-tension is still maxed out. Every gear *appears* to work (albeit the pulley is quite close), except for the lowest possible gear combo (little chainring, big cog). It is clicking and bumping on the rear derailleur. The cassette cog is clearly passing within the frame of the pulleys. I get the feeling that, yeah, my chain might have been a tad bit longer than average, but something else is going on.
Your problem is you are stil two links too long. You said you're too long by 4 links but you only took off two. The chain isnt tensed enough to pull the cage away from the cog. Probably does the same on the opposite (small cog big ring) too.

I had problems on my road bike by being 1 link to short, if only 1 link can cause issues, then 2 links long or short will DEFINITELY cause issues.
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Old 09-28-09, 10:30 AM   #17
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What is being overlooked here is that the RD hanger is not necessarily the same on all frames and neither is the stop that the B screw rests against. You may simply need a longer screw to compensate for an error in the frame.
I'm with Dave on this one. Stop pulling links out of your chain and use a longer screw/flip the screw over. Problem solved and you don't have to use a new chain if you want to swap between two sizes of cassettes.
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Old 09-28-09, 10:32 AM   #18
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You should have checked the little/little for sag or rubbing BEFORE you took off an inch of chain. If there was no rub or sag, the chain was not too long. I still say that the problem is unrelated to chain length.

There is ONE length that will handle any cassette from an 11-21 to a 12-27. There is never a need to change the chain length. It would NEVER be shortened to use a 12-27.

As an example, I have the true maximum wrap with my Campy 11 speed bike. I have a 50/34 with a 12-27 on a short cage RD. The same 53 inch chain will also work perfectly with an 11-23.

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Old 09-28-09, 10:33 AM   #19
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Some shimano road rear derailers are rated to only 26T. See techdocs.shimano.com for the specs on whichever model you have.
According to techdocs - largest sprocket = 28T.
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Old 09-28-09, 10:34 AM   #20
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You should have checked the little/little for sag or rubbing BEFORE you took out an inch of chain. If there wasno rub or sag, the chain was not too long. I still say that the problem is unrelated to chain length.
Fortunately, I did. It was barely rubbing on the top pulley.
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Old 09-28-09, 10:37 AM   #21
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look at the install instructions for the DR, I think it shows the proper chain length should allow a vertical position for the line of the axles of the tension and guide pulleys when in the small sprocket on the casette and the big ring
Bud

Last edited by oldster; 09-28-09 at 10:44 AM. Reason: add on the big ring
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Old 09-28-09, 10:40 AM   #22
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Fortunately, I did. It was barely rubbing on the top pulley.
OK, then the chain was an inch too long, but now it is the correct length. Do not shorten it any more. Shortening it will reduce the wrap capacity.

You probably just need a longer B screw. It should be a common M4 thread that you can get at Ace hardware. Some people do a crude fix by turning the screw upside down so the head rests on the frame.
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Old 09-28-09, 11:06 AM   #23
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OK, then the chain was an inch too long, but now it is the correct length. Do not shorten it any more. Shortening it will reduce the wrap capacity.

You probably just need a longer B screw. It should be a common M4 thread that you can get at Ace hardware. Some people do a crude fix by turning the screw upside down so the head rests on the frame.
I tried the screw upside down, and only screwed it in a few threads. Looking from the side, the largest sprocket is just breaking "the plane" of the top pulley derailleur cage. I can't tell if it's actually hitting - but I don't hear clicking. Still, probably too close for comfort. I will try to rummage through my spare bolts.

As a side note, I also replaced my ultegra pulleys with forte metal pulleys. I don't know how wise this was - seems much noiser than before. I don't think this has anything to do with the pulleys hitting the sprocket - just figured I'd mention it.
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Old 09-28-09, 11:35 AM   #24
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Checked out the B-tension bolt on my mountain bike - it was a little longer. Swapped it with my road bike bolt - screwed in the regular way (to the max), the spacing is about the same as the other screw upside down. It is kinda the law of diminishing returns here - a curved/bent bolt would probably be more effective.

Just how much space is the minimum between the sprocket and pulley? I'm wondering if it is adequate if I'm not hearing anything. But it sure is close!
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Old 09-28-09, 11:40 AM   #25
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Is your derailer hanger bent?

If not, is this a steel frame with "thin" drop-outs? Maybe you could try spacing the rear derailer more outboard from the frame. You'd also need to adjust your "H" and "L" screws. It might get the derailer to ride a little further down and away from the large cog.
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