My chain won't engage with the second largest cog and skips over to the largest one

[Llewellyn]

I've got my Dura Ace rear derailleur on my 9 speed Lynskey set up and it shifts really well on all the cogs except the two largest ones. When it's on the third largest cog and I press the lever to go up to the second largest, it doesn't engage and shifts straight over to the largest cog, and the same thing happens if I shift it the other way.

But it works fine on all the others. I've tried adjusting the tension at the barrel adjuster and fiddling with the limit screws but neither of those helped. Any ideas what might be going on and how I fix it? Thanks

[WickedWheels]

bent hanger, bent derailleur or cable housing that's crapping out (some of the metal strands unevenly poking through then housing ferrules)... most likely

[eddief]

last time I had cog skipping issues, I adjusted and adjusted and got nowhere. on a lark, I thought new chain? New chain fixed it.

[rustychisel]

B screw affecting upper jockey wheel clearance on 9 speed derailleur, depending on what size cogs on that cassette.

[Llewellyn]

B screw affecting upper jockey wheel clearance on 9 speed derailleur, depending on what size cogs on that cassette.

12 - 23. The B screw is the one that sticks out the back of the derailleur hanger - is that right?

[rustychisel]

Yeah, but on a 12 - 23 it's unlikely. The B screw adjusts derailleur body angle and that affects the jockeys... if they brush the bottom of the cassette it'll usually be on those larger cogs.

Check alignments, make sure cables are seated all along their run... I once had a bike which exhibited similar problems and eventually found the housing ferrule which located into the stop on the chainstay was out of its recess. Check the cable runs loose and good, too.

Not going to be the limit screw if it jumps over the 21 to the 23.

incidentally,
On a Campagnolo bike we just had an issue with a Connex link not playing nicely with a new Centaur cassette, it jumped on 3 biggest cogs. Have just replaced chain and used KMC chain and quicklink - seems to have sorted it.

[oldpotatoe]

I've got my Dura Ace rear derailleur on my 9 speed Lynskey set up and it shifts really well on all the cogs except the two largest ones. When it's on the third largest cog and I press the lever to go up to the second largest, it doesn't engage and shifts straight over to the largest cog, and the same thing happens if I shift it the other way.

But it works fine on all the others. I've tried adjusting the tension at the barrel adjuster and fiddling with the limit screws but neither of those helped. Any ideas what might be going on and how I fix it? Thanks

shifters and cogset/chain not match..9s-10s-9s?

Which shifter and rear der?

Cable not attached properly to Rear der,.....under the bolt and plate,not thru it?

Der hanger?

[victoryfactory]

Chain has sticky link or 1 link too short?
I'd check the B screw too.
Missing spacer under cassette?
loose or gunked up or damaged rings?
Careful fiddling with B screw, though Those things strip. Use a proper
size, high quality screw driver. IMO, they should use Allen head screws
on all the derailleur adjusters.
Attention entrepreneurs with more energy than me:
Market high quality Allen head adjuster screw replacement sets.
Create a small counter display stand. Go on a road trip to every pro shop in
the country. Everybody wants this! 2.00 worth of screws in a plastic bag
for 11.95 retail.
Thread drift Friday!

Good luck

VF

[Oregonic]

bent hanger, bent derailleur or cable housing that's crapping out (some of the metal strands unevenly poking through then housing ferrules)... most likely

This. If you don't have a hanger alignment tool, take it to the lbs and have it checked. Could be a 5 min fix.

[eddief]

when I wanted a longer b-screw, of course they had a replacement...and the one they had had a hex head. the hex works great when tightening against the chain tension and spring tension of the r d. Minor bummer is the bolt they had in stock had a plain black finish and it quickly rusted. no big deal, but chromed or stainless woud be even better.

Chain has sticky link or 1 link too short?
I'd check the B screw too.
Missing spacer under cassette?
loose or gunked up or damaged rings?
Careful fiddling with B screw, though Those things strip. Use a proper
size, high quality screw driver. IMO, they should use Allen head screws
on all the derailleur adjusters.
Attention entrepreneurs with more energy than me:
Market high quality Allen head adjuster screw replacement sets.
Create a small counter display stand. Go on a road trip to every pro shop in
the country. Everybody wants this! 2.00 worth of screws in a plastic bag
for 11.95 retail.
Thread drift Friday!

Good luck

VF

[lhuerta]

Need more information....did you change any parts recently? Did the bike fall over on the drive side lately? Did this just start to happen with regular use or is it something that has been developing bit by bit? I ask because in addition to all the good suggestions above, it is possible that your chain is worn or that your shifter mechanism is shot, but still need more info to determine and provide a more tailored diagnosis. Lou

[pakora]

This. If you don't have a hanger alignment tool, take it to the lbs and have it checked. Could be a 5 min fix.

I've had this happen to me, and a friend just had the exact same problem and I think even with the same parts you're using.

In both cases the hanger looked straight, and when a shop used a hanger alignment tool, they shifted perfectly immediately after.

[Ralph]

It could be a lot of things...as noted above. But I would bet it's an adjustment issue. It's off on the small cog stop, and/or barrel adjuster is off....and the amount "off" just stacks up until it won't do a cog....then jumps to another.

RE the B screw....RD usually shift best when you position the upper pulley as close to the larger cogs as possible, without bumping on it.

[carpediemracing]

My first instinct for a slightly-malfunctioning-but-otherwise-properly-setup rear derailleur is to stick an allen wrench in the mounting bolt and twist it up a nudge. Virtually all derailleur hangers will bend in over time, just a touch. I can't tell you why and I don't have any scientific proof, just seeing thousands of them over the years in a bike shop.

Tweaking the hanger up will make it a touch more vertical. This miraculously cures a lot of shifting ailments.

A friend and fellow bike shop/industry veteran calls it "the magic touch". It's just like magic, it works but like magic it's hard to explain why.

Disclaimer: if you nudge too hard you're going to break something or at the very least you'll really bend the dropout. If you don't nudge enough then nothing happens. Nudge gently, check, nudge a bit harder, check, and when it miraculously works perfectly then leave it alone.

[lhuerta]

My first instinct for a slightly-malfunctioning-but-otherwise-properly-setup rear derailleur is to stick an allen wrench in the mounting bolt and twist it up a nudge. Virtually all derailleur hangers will bend in over time, just a touch. I can't tell you why and I don't have any scientific proof, just seeing thousands of them over the years in a bike shop.

Tweaking the hanger up will make it a touch more vertical. This miraculously cures a lot of shifting ailments.

A friend and fellow bike shop/industry veteran calls it "the magic touch". It's just like magic, it works but like magic it's hard to explain why.

Disclaimer: if you nudge too hard you're going to break something or at the very least you'll really bend the dropout. If you don't nudge enough then nothing happens. Nudge gently, check, nudge a bit harder, check, and when it miraculously works perfectly then leave it alone.


No offense carpediemracing, but this is poor advice all around, Yes, I agree, hangers are subject to bend, especially when leaning bikes against walls and not inspecting after dropping on drive side. But aligning hanger by sticking an allen wrench in the mounting bolt and twisting is not wise advice, especially with today's more common Ti and Alum mounting bolts. The proper approach is to simply use the $50 Park DAG-1 hanger tool, which requires you to remove rear mech, mount tool and then gently use torque to bend the hanger in to alignment. Today's 10 and 11 speed systems are more sensitive to mis-alignment and demand perfect alignment for precise shifting.

Any "mechanic" who is using the method you describe should be taken out back and beaten with a DAG-1 tool :no:

Lou

[oldpotatoe]

My first instinct for a slightly-malfunctioning-but-otherwise-properly-setup rear derailleur is to stick an allen wrench in the mounting bolt and twist it up a nudge. Virtually all derailleur hangers will bend in over time, just a touch. I can't tell you why and I don't have any scientific proof, just seeing thousands of them over the years in a bike shop.

Tweaking the hanger up will make it a touch more vertical. This miraculously cures a lot of shifting ailments.

A friend and fellow bike shop/industry veteran calls it "the magic touch". It's just like magic, it works but like magic it's hard to explain why.

Disclaimer: if you nudge too hard you're going to break something or at the very least you'll really bend the dropout. If you don't nudge enough then nothing happens. Nudge gently, check, nudge a bit harder, check, and when it miraculously works perfectly then leave it alone.

Or, just use a proper tool to measure and then align der hanger..no magic involved.

[Llewellyn]

Thanks for all the advice guys. To answer a few of the questions raised - it's 9 speed Ultegra shifters and a Dura Ace RD (new cassette but a low km's pre-used chain) on a new frame that I've just built up and hasn't been dropped or crashed. Up until now I've only done a couple of shortish test rides and I only noticed the problem yesterday when I had the bike in the stand and was running through all the gears.

I'll check the cable position at the RD but if it's not that then it sounds like a bent hanger is a definite possibility and I'll drop it in to an LBS and get them to have a look - they'll have the right tools.

[carpediemracing]

I don't carry an alignment tool with me everywhere I go and in fact I don't think I own one now. The wrench-in-the-derailleur is very quick, literally a couple seconds, and it's done. The nice thing is that you can make someone's day by fixing a bike in the parking lot just before a group ride rolls out or a race goes off etc.

I understand the weaker hangers, Ti/alum bolts, etc. I don't have 11s but I've done it on 10s bikes (ti bolts, no aluminum, with alum replaceable hangers or steel non replaceable ones), mine and others, and of course on older bikes.

Also although I understand what happens and what I want to accomplish it doesn't mean that other people do, hence the "magic" bit. A mechanic friend asked me to check his bike because his derailleur was just a bit off. I would have ridden it the way it was but I noticed his pulleys weren't lined up under the cogs. One tweak and it was better, some minor cable tension adjustment and it was shifting "well" (according to him). That was when he made the "magic" remark. I look at how a derailleur uses its pulleys to guide the chain onto the cogs in various positions and try to make the derailleur work best using the things I observe.

Of course ask me about my regularly-creaky BB30 and that's a different story.

[rustychisel]

I don't carry an alignment tool with me everywhere I go and in fact I don't think I own one now. The wrench-in-the-derailleur is very quick, literally a couple seconds, and it's done. The nice thing is that you can make someone's day by fixing a bike in the parking lot just before a group ride rolls out or a race goes off etc.

I understand the weaker hangers, Ti/alum bolts, etc. I don't have 11s but I've done it on 10s bikes (ti bolts, no aluminum, with alum replaceable hangers or steel non replaceable ones), mine and others, and of course on older bikes.

Also although I understand what happens and what I want to accomplish it doesn't mean that other people do, hence the "magic" bit. A mechanic friend asked me to check his bike because his derailleur was just a bit off. I would have ridden it the way it was but I noticed his pulleys weren't lined up under the cogs. One tweak and it was better, some minor cable tension adjustment and it was shifting "well" (according to him). That was when he made the "magic" remark. I look at how a derailleur uses its pulleys to guide the chain onto the cogs in various positions and try to make the derailleur work best using the things I observe.

Of course ask me about my regularly-creaky BB30 and that's a different story.


Of course. Amazing how often on a group ride you're behind someone and notice how their jockey wheels are offline... 'drop your bike on the drive side recently?'

"err, yeah. Last week. Why?"