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Trouble shifting only into certain rear gears

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Trouble shifting only into certain rear gears

Old 07-01-20, 01:55 PM
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CosmicThespian
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Trouble shifting only into certain rear gears

Hello! I'm having trouble shifting the rear cassette, but only into two specific gears and only when shifting in one direction. I have a 9-speed cassette, and when I'm shifting up (to smaller, harder gears), the chain won't shift from gear 2 to 3 or from 6 to 7. If I want to get into 3 from 2, I have to shift again to 4, and then back down to 3. Same for getting into gear 7. Adjusting the cable tension via the barrel adjuster just throws off shifting into all the other gears. What's really frustrating is that I can't replicate it when I'm at home working on it. I don't have a bike stand, so I flip the bike upside down and shift through all the gears while moving the pedals and it seems to work fine. On the road though, the shifting problem comes back.

I've visually inspected the cable and housing, and they look OK to me. The rear derailleur looks good, no sign of it being bent or out of alignment. Those two cogs on the cassette look OK to me as well. I'm out of ideas. Any thoughts on what might cause trouble upshifting into only two particular gears???

Relevant background: Bike is a Specialized Sirrus Sport (hybrid), about five years old. I replaced the chain a couple of weeks ago, after which my rear shifting was all screwed up (which I attributed to possibly nudging the derailleur out of alignment while giving it a good cleaning while the chain was off) but I was able to get the shifting mostly back with a barrel adjustment, except for these two cogs.
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Old 07-01-20, 02:08 PM
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When I had similar issues going from low to high on the back, it was because of too much binding on the cables in various places and the DR couldn't move quick enough so I'd give it a little more lever . This mainly happened when I was using friction shifters and before I ventured in to the world of indexed shifting. However I did also have it happen once with indexed shifters. Again it was the cable not moving freely.

While I have nothing against turning a bike upside down. Others will crucify you for it. But I will add that trying to adjust the shifting while upside down is sketchy at best. Gravity does play a role here. So have it right side up when adjusting. Though the other thing that you don't get is simulating the forces of pedaling to duplicate what the DR's experience on the road.
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Old 07-01-20, 02:15 PM
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KevinF
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So it worked great until you replaced the chain? If you were getting aggressive with your derailleur cleaning you could have bent the derailleur hanger (i.e, the thing that the derailleur itself is bolted onto), but that generally takes some force (i.e., crashing). Big chunks of metal don't usually just bend though and finding if it's bent involves tools most people don't have at home.

It's possible the bolt that fixes the derailleur onto the frame has worked its way loose? That happened to me a few weeks back; retightening the bolt that connects the derailleur to the frame made it all good. It's usually just an 8mm allen key.
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Old 07-01-20, 02:29 PM
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The huge majority of RDs shift to smaller sprockets by a spring in the RD. The shift happens when the shifter feeds out cable. If you have trouble shifting in that direction the most common reason is the cable not moving freely.
IMO it’s so common that even I only spend a very limited effort on finding other reasons before replacing cables. At least the outer cable closest to the RD.
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Old 07-02-20, 07:58 AM
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CosmicThespian
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Thanks for the insights everyone. I'm still running with the original cable, so maybe it's way past time to just suck it up and replace it! I'll give that a try, and I'll also check the bolt that fixes the derailleur onto the frame (per KevinF's suggestion). I'll be sure to check back in and report how it goes...
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Old 07-02-20, 08:53 AM
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Originally Posted by CosmicThespian
Hello! I'm having trouble shifting the rear cassette, but only into two specific gears and only when shifting in one direction. I have a 9-speed cassette, and when I'm shifting up (to smaller, harder gears), the chain won't shift from gear 2 to 3 or from 6 to 7. If I want to get into 3 from 2, I have to shift again to 4, and then back down to 3. Same for getting into gear 7. Adjusting the cable tension via the barrel adjuster just throws off shifting into all the other gears. What's really frustrating is that I can't replicate it when I'm at home working on it. I don't have a bike stand, so I flip the bike upside down and shift through all the gears while moving the pedals and it seems to work fine. On the road though, the shifting problem comes back.
Most likely your shift cable is frayed, housing worn, or housing dirty. Changing chains could have exacerbated the problem with your new one having less flexibility from no lateral wear, a different width, or different side plate profile.

Shifting like I have ADHD I have to change rear shift cables at 2000 miles so they don't break from fraying, and could push the housing to 4000 but maintain optimum shift performance just swapping it with the cable.

The rear loop can also gunk up from road dirt. You need a foot (330mm) there so the radius isn't too tight producing high friction.

Bulk housing and individual rear shift cables are inexpensive, even Campagnolo brand.

Last edited by Drew Eckhardt; 07-05-20 at 09:34 AM.
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Old 07-03-20, 10:16 AM
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If you were riding that bike with the same drivetrain for 5 years, you probably have a very worn cassette which has "bonded" with the old chain. The new chain would not work well with the old, worn cassette and this could cause the difficulty shifting, especially down the gear range. A new nine-speed cassette can be had for less than thirty bucks, and if your current one is five years old it's definitely time.

Depending on how many miles you have on it, you might be facing a similar issue with your front chainrings. Give them a look, and see if the teeth are developing "shark fin" profile. When that happens, the chainring will start to hold on to the chain for a microsecond at the end of the rotation when power is applied, and the chain will jerk or jump when it releases from the chainring, causing an aggravating bang noise in your drivetrain that can feel like a skipping shift. This is a nightmare to diagnose sometimes, because it won't happen when the bike is on the stand, only when the chain is under load. It doesn't sound like you have this problem yet, but with a five year old drivetrain, it's gonna happen at some point.
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Old 07-03-20, 11:42 AM
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I agree cassette wear could be an issue, but more likely a cable/housing issue. Especially the rear loop as mentioned. That reminds me, I need to replace mine for a similar issue. I can keep on top of it with frequent cleaning and lubrication but the housing needs to be replaced.
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Old 07-03-20, 12:31 PM
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Originally Posted by andrewclaus
I agree cassette wear could be an issue, but more likely a cable/housing issue. Especially the rear loop as mentioned. That reminds me, I need to replace mine for a similar issue. I can keep on top of it with frequent cleaning and lubrication but the housing needs to be replaced.
Certainly, sticky cables could be the culprit (and a nice cheap replacement), but I was focusing on the fact that the shifting problem did not manifest until OP changed the chain. Sticky cables would be an issue no matter what chain he used, while a problem that started after a chain replacement suggests a compatibility issue between the new chain and the old cassette.

I have found on Amazon that I can buy a ten-pack of Shimano shifter cables for $24, and a coil of 4mm Jagwire housing for another $20 or so. That makes changing cables/housing easy and cheap, especially when you see what they charge for a package of cable, housing and a couple ferrules.
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Old 07-29-20, 09:40 AM
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Thank you everyone for your thoughts. Just wanted to report back that I replaced the shifting cables and housing -- and problem solved!

I'm still making some tweaks to the tension as the new cables 'settle in', but the main problem is gone. So for anyone else who stumbles on to this thread with a shifting issue: even if your cable 'looks' fine, try replacing it. It's an easy and inexpensive fix.
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