Slipping / jumping in 11 tooth gear

[m_cawein]

Hello, I'm a road biker (about 6500 miles/year). I recently replaced my Dura Ace 10s chain with a new Dura-Ace 10s chain. I also replaced the cassette because it was time. I decided to go a little cheaper and replace my Dura-Ace 27-12 cassette with an Ultegra 28-11 (Ultegra has no 27-xx options). I figured I might have an issue with the 28 tooth gear because I'm running Dura-Ace 7800 drivetrain intended for maximum 27 tooth. Actually I have no problem with the 28, but rather with the 11. All gears except the 11 are perfect. The 11 slips every few seconds (it varies, sometimes 10-15 sec, other times every 3 sec). I cannot tell if its really a slip or a false shift. I made numerous adjustment attempts but the 11 always does this. I'm wondering if the problem is a very slight misalignment of my derailleur hanger. I crashed about 3 years ago and my derailleur did get a small grind on the body. I never had an issue with a 12 tooth as my smallest gear. I will check out the hanger sometime this week, but I'm just wondering if anybody else has seen issues with 11 tooth gearing. Any Ideas ?

[RobAR]

Hi m_c. What you describe is a classic symptom of a bent hanger BUT, I find it unusual that it would only now make itself known after 3 years.
The first thing that I would check is the drlr pulleys. Make certain that they spin freely. Then inspect the chain for any tight links.
If that checks good - you sound as though you may know what the B Tension screw on the RD is. If the chain drops easily onto the 11, you may need a minor adjustment of the B Screw to allow more chain-wrap on that smaller cog.

Let us know!

Edit - BTW, which cassette and chain did you install? Model numbers?

[m_cawein]

(04-04-2011, 08:50 PM)RobAR Wrote:  Hi m_c. What you describe is a classic symptom of a bent hanger BUT, I find it unusual that it would only now make itself known after 3 years.
The first thing that I would check is the drlr pulleys. Make certain that they spin freely. Then inspect the chain for any tight links.
If that checks good - you sound as though you may know what the B Tension screw on the RD is. If the chain drops easily onto the 11, you may need a minor adjustment of the B Screw to allow more chain-wrap on that smaller cog.

Let us know!

Edit - BTW, which cassette and chain did you install? Model numbers?

Hi Rob, The old and new chains are Dura-Ace 7900. The new cassette is the Ultegra 6700 series. The jockey pulleys spin great and I checked all links on the chain.
I played with the bottom end limit screw, but not the tension screw. I'll do that tonight. Thanks for that suggestion.
I agree that it's weird that after running so long with 27-12 cassettes, I switch to 28-11 and have a problem with the 11.
When I made the change to the new parts, I first used my trusty old wipperman connex link which works fantastic with Dura-Ace 10s chains. When I discovered the problem, I thought maybe that link has finally stretched too much, so I switched to the pins that come with the chain. They worked fine with no tight links, but the problem still persisted.
I'll report back with my findings on the tension screw and the hanger alignment. Thx Again.

[RobAR]

m_c, you are aware that the 7900 and 6700 chains are 'directional', yes? The inner and outer plates are diff to maximize shifting performance. In your case though, I still suspect the B Tension adj. Putting a 79 or 67 on backwards would not cause a problem in only the 11. Just a thought...

[m_cawein]

(04-05-2011, 08:24 PM)RobAR Wrote:  m_c, you are aware that the 7900 and 6700 chains are 'directional', yes? The inner and outer plates are diff to maximize shifting performance. In your case though, I still suspect the B Tension adj. Putting a 79 or 67 on backwards would not cause a problem in only the 11. Just a thought...

Rob, Yep, I have the chain on the correct way. I have not ridden that bike yet since I released tension on the RD (I'm riding my rain bike this week). I found info somewhere on the web that Shimano hubs have the same threads that the RD uses to attach to the hanger. I grabbed an old wheel around my shop and tried it and it works great as a hanger alignment test tool. I threaded the wheel to the RD hanger and snugged it up. I could clearly see that at the far back (9:00 position) there is a larger gap between the test wheel and my bike's rim than there is at the far front (3:00 position). I rotated both wheels 180 degrees to eliminate error from either wheel being untrue. Still, I measure about an inch of difference. This shows that my hanger is slightly out of alignment. Tonight I'll tweak it into alignment in small increments (don't want to break off the aluminum non-replaceable hanger). Hopefully this weekend I'll get this thing out and see if either change has fixed the problem. If the problem is gone, I'll probably re-tension the RD to max tension (that's what I had it set to) and see which change fixed it. I'll let you know. Thx

[m_cawein]

The problem has been resolved. It seems that the derailleur hanger was twisted just enough to cause occasional slip/jump of the chain in the 11 tooth sprocket. I released the tension screw and made the alignment fix to the hanger at the same time. When I did my 1st test ride of 60 miles, the problem was gone, but I also tried running full granny again and could hear much more noise with the 28. That was due to the reduced tension on the derailleur. I changed the tension back to full and did a 50 mile test ride and now the 11 tooth and 28 tooth problems are gone. Thanks for the input.