Bikefilter: skipping chain
February 8, 2021 7:54 AM Subscribe
Halp me fix or decide to replace drivetrain, please! I just replaced the cassette and chain, so I'm not sure what's next.
One of my quiver is a 2004ish custom steel road bike, which I bought new with an Ultegra 9-speed drivetrain. I've replaced the chain every so often and the pulleys, but otherwise original parts on the drivetrain.
Fast forward several miles/years, over which bike gets used regularly, and gets mounted onto a simple magnetic trainer every winter.
This fall, the chain started skipping on the 8th cog -- would not stay on that one. I got ambitious, ordered the tools, and replaced the cassette and chain with a SRAM PG950 cassette and a Shimano HG53 chain, both 9-speed.
Now: the chain stays on the 8th cog just fine. It shifts fine, generally, over the whole range, no rubbing. But now it skips and won't stay on the 6th cog.
What now? I can't see anything clearly amiss with the cassette or any teeth.
What now, part II: the original drivetrain is a triple. Should I consider replacing the entire drivetrain, with a compact double, or a 1x (is that a thing for road bikes)? My much newer mountain bike is a 1x11, and that's been super smooth to get used to, and boy it's sure nice to not have to shift chainrings.
One of my quiver is a 2004ish custom steel road bike, which I bought new with an Ultegra 9-speed drivetrain. I've replaced the chain every so often and the pulleys, but otherwise original parts on the drivetrain.
Fast forward several miles/years, over which bike gets used regularly, and gets mounted onto a simple magnetic trainer every winter.
This fall, the chain started skipping on the 8th cog -- would not stay on that one. I got ambitious, ordered the tools, and replaced the cassette and chain with a SRAM PG950 cassette and a Shimano HG53 chain, both 9-speed.
Now: the chain stays on the 8th cog just fine. It shifts fine, generally, over the whole range, no rubbing. But now it skips and won't stay on the 6th cog.
What now? I can't see anything clearly amiss with the cassette or any teeth.
What now, part II: the original drivetrain is a triple. Should I consider replacing the entire drivetrain, with a compact double, or a 1x (is that a thing for road bikes)? My much newer mountain bike is a 1x11, and that's been super smooth to get used to, and boy it's sure nice to not have to shift chainrings.
I’m assuming you’ve tried indexing your gears and adjusting the limiter screws on the front and back derailleur?
[handy video if not]
Shifter cables stretch out over time and the gears need re-indexing even if all the other parts are perfectly maintained.. Additionally, gears need to be re-indexed every time you swap out the cassette.
posted by blueberrypuffin at 8:41 AM on February 8, 2021
[handy video if not]
Shifter cables stretch out over time and the gears need re-indexing even if all the other parts are perfectly maintained.. Additionally, gears need to be re-indexed every time you swap out the cassette.
posted by blueberrypuffin at 8:41 AM on February 8, 2021
Response by poster: I did not replace the cable -- the derailleur is original, nothing different there.
The cog that's skipping is in the middle of the cassette, and the derailleur is working perfectly (ie, no noises, chain well aligned) for all other cogs, so I don't think the barrel or limiters need adjustment?
posted by Dashy at 8:47 AM on February 8, 2021
The cog that's skipping is in the middle of the cassette, and the derailleur is working perfectly (ie, no noises, chain well aligned) for all other cogs, so I don't think the barrel or limiters need adjustment?
posted by Dashy at 8:47 AM on February 8, 2021
When my bike requires re-indexing, it’s usually the middle gears that start skipping! Try it :-) a quick and dirty way I do it is to bring my bike to a low-angle (but not flat), low-traffic area, turn my barrel adjuster one direction a quarter turn and see if it gets better or not, then keep turning it in it’s-getting-better-direction until it feels smooth again.
posted by blueberrypuffin at 8:49 AM on February 8, 2021 [1 favorite]
posted by blueberrypuffin at 8:49 AM on February 8, 2021 [1 favorite]
Might want to also check to see if the derailleur hanger needs to be straightened. Sometimes that can get bent if the bike has ever fallen on its right side or been jostled around. Take a really good look at the hanger and make sure it’s absolutely parallel to the bike. Even being the slightest bit bent could cause weird gear behavior. Fixing this requires a special tool that any bike shop should have, and should take less than 1/2 hour.
posted by oxisos at 9:28 AM on February 8, 2021 [1 favorite]
posted by oxisos at 9:28 AM on February 8, 2021 [1 favorite]
Skipping in the 8th cog has nothing to do with limit screws. Could be cable tension. Could be misaligned derailleur. Could be chain and/or cassette wear.
You check and adjust the derailleur hanger with this tool. You take the derailleur off, screw the tool into the hanger, then check the distance of the gauge from the rim at 12/3/6/9 o'clock orientations. You can bend the hanger to align it. It's made of a softer material and it's meant to break before your frame does. Typically you can buy them for $10-$30 each if yours can't be bent (they have a limit and will start to crack). You mention this is a custom bike, but I don't know if you mean it's just a boutique build with components selected or if it's actually a custom frame. If it's a custom frame, finding a replacement hanger might be a challenge.
You can check chain wear with a tool like (go/no go gauge) this or like this (variable gauge). Note: chains wear faster than cassettes. If your cassette is severely worn, a new chain won't fix the issue. Replacing your chain sooner rather than later can increase the service interval for your cassette.
Now, for the part you can do without any tools: checking the cable tension. I'm going to call the smallest (physically smallest, aka your highest gears, aka the cogs on the cassette farthest to the right when you're standing over your bike) the A, B, and C cogs. So A is the 9th gear, B is the 8th, C the 7th. The three physically biggest gears are going to be X, Y, and Z in ascending order, so Z is 1st gear, the physically biggest cog, the cog closest to the centerline of the bike.
1)Put the bike in a stand. You can use the trainer for this, but remove all tension from the wheel so the trainer doesn't make any noise or give any resistance. Shift into the B cog (8th gear). Loosen the barrel adjustor while until you hear a noise indicating that the chain is ALMOST READY to jump down to the A cog. Now you know the cable tension is TOO LOOSE.
2) While pedaling the bike, start to increase cable tension. The noise will go away, then it'll start happening again as the chain wants to jump up to the C cog. Now you know the tension is TOO TIGHT.
3) While pedaling the bike, back the tension off just a little until the noise JUST DISAPPEARS. Now you know the tension is just right.
4) Now check the tension through the whole cassette. Shift up to the highest gear, then shift down through the cassette one gear at a time and see how the shifting responds. If some gears make a noise, you know the tension isn't too loose, remember? It's as tight as it can be, so loosen it an eighth of a turn and see if it goes away. Repeat for all the gears. If the problem persists, you have something else other than cable tension going on.
posted by spikeleemajortomdickandharryconnickjrmints at 9:59 AM on February 8, 2021 [1 favorite]
You check and adjust the derailleur hanger with this tool. You take the derailleur off, screw the tool into the hanger, then check the distance of the gauge from the rim at 12/3/6/9 o'clock orientations. You can bend the hanger to align it. It's made of a softer material and it's meant to break before your frame does. Typically you can buy them for $10-$30 each if yours can't be bent (they have a limit and will start to crack). You mention this is a custom bike, but I don't know if you mean it's just a boutique build with components selected or if it's actually a custom frame. If it's a custom frame, finding a replacement hanger might be a challenge.
You can check chain wear with a tool like (go/no go gauge) this or like this (variable gauge). Note: chains wear faster than cassettes. If your cassette is severely worn, a new chain won't fix the issue. Replacing your chain sooner rather than later can increase the service interval for your cassette.
Now, for the part you can do without any tools: checking the cable tension. I'm going to call the smallest (physically smallest, aka your highest gears, aka the cogs on the cassette farthest to the right when you're standing over your bike) the A, B, and C cogs. So A is the 9th gear, B is the 8th, C the 7th. The three physically biggest gears are going to be X, Y, and Z in ascending order, so Z is 1st gear, the physically biggest cog, the cog closest to the centerline of the bike.
1)Put the bike in a stand. You can use the trainer for this, but remove all tension from the wheel so the trainer doesn't make any noise or give any resistance. Shift into the B cog (8th gear). Loosen the barrel adjustor while until you hear a noise indicating that the chain is ALMOST READY to jump down to the A cog. Now you know the cable tension is TOO LOOSE.
2) While pedaling the bike, start to increase cable tension. The noise will go away, then it'll start happening again as the chain wants to jump up to the C cog. Now you know the tension is TOO TIGHT.
3) While pedaling the bike, back the tension off just a little until the noise JUST DISAPPEARS. Now you know the tension is just right.
4) Now check the tension through the whole cassette. Shift up to the highest gear, then shift down through the cassette one gear at a time and see how the shifting responds. If some gears make a noise, you know the tension isn't too loose, remember? It's as tight as it can be, so loosen it an eighth of a turn and see if it goes away. Repeat for all the gears. If the problem persists, you have something else other than cable tension going on.
posted by spikeleemajortomdickandharryconnickjrmints at 9:59 AM on February 8, 2021 [1 favorite]
Oh yeah, it also might be a little bit of all those things combined. Nothing so bad that on its own it makes the chain skip, but when combined with everything else being slightly out of whack you notice it. Start with cable tension.
Oh, something else, if it shifts down (to bigger cogs) just fine but doesn't want to shift up (to smaller cogs) without a bit of hesitation, that can be caused by friction in the cable and housing. Replacing the cable and housing (~$4 for the cable, ~$1.50/ft for the housing, ~$0.50/ferrule, ~$0.10 for the cable crimp, plus QUALITY cable cutters meant for bike housing) will fix that right up. It can also be caused by a weak return spring in your derailleur, which is about 17 years old at this point, and totally understandable. I got about 12 years out of my 9spd Ultegra. I replaced it with a 10spd 105 and it worked perfectly (theoretically it shouldn't, but it did).
posted by spikeleemajortomdickandharryconnickjrmints at 5:19 PM on February 8, 2021
Oh, something else, if it shifts down (to bigger cogs) just fine but doesn't want to shift up (to smaller cogs) without a bit of hesitation, that can be caused by friction in the cable and housing. Replacing the cable and housing (~$4 for the cable, ~$1.50/ft for the housing, ~$0.50/ferrule, ~$0.10 for the cable crimp, plus QUALITY cable cutters meant for bike housing) will fix that right up. It can also be caused by a weak return spring in your derailleur, which is about 17 years old at this point, and totally understandable. I got about 12 years out of my 9spd Ultegra. I replaced it with a 10spd 105 and it worked perfectly (theoretically it shouldn't, but it did).
posted by spikeleemajortomdickandharryconnickjrmints at 5:19 PM on February 8, 2021
Poor indexing on a specific mid-range gear is usually, in order of decreasing odds:
- poor adjustment: it's good enough in most gears but some combination of small errors adds up in one spot; similarly, excessive gap from the B screw will show up more in certain gears in a non-corncob cassette (the parallelogram may not follow the cassette profile perfectly)
- QR or thru-axle adjusted poorly: e.g., an under-tensioned QR skewer means gears and derailleur travel don't stay parallel.
- dirt, grit, fossilized grease, worn plastic: usually on the gear face, usually in the rear derailleur (imagine some crud on the cam), sometimes on the cable or in the cable housing (imagine pulling a cable through a gouged lining), occasionally in the shifter.
- a bent tooth in that gear, damaged or incorrect spacer for that gear, etc., that's putting it juuust out of place
- derailleur that's not hanging straight: like excessive gap from the B screw, this will often confusingly show up in middle gears where the gap is greatest or chain deflection force is highest
- derailleur that's otherwise damaged: e.g., idler pulley whose bushing is totally shot so it deflects under certain tension
So: clean it (while moving the derailleur in and out), lightly oil the derailleur pivot points (people will yell about this but your bike is old enough that you can ignore them), blow a little air into the shifter while indexing it back and forth, check all shifter adjustments, eyeball the gear teeth and derailleur hanger and derailleur pivot. When in doubt, run new housing and cables the bike if it's been more than a couplefew years since you've done so. Then start fine-checking all the little details like derailleur hanger straightness.
posted by introp at 12:03 PM on February 9, 2021
- poor adjustment: it's good enough in most gears but some combination of small errors adds up in one spot; similarly, excessive gap from the B screw will show up more in certain gears in a non-corncob cassette (the parallelogram may not follow the cassette profile perfectly)
- QR or thru-axle adjusted poorly: e.g., an under-tensioned QR skewer means gears and derailleur travel don't stay parallel.
- dirt, grit, fossilized grease, worn plastic: usually on the gear face, usually in the rear derailleur (imagine some crud on the cam), sometimes on the cable or in the cable housing (imagine pulling a cable through a gouged lining), occasionally in the shifter.
- a bent tooth in that gear, damaged or incorrect spacer for that gear, etc., that's putting it juuust out of place
- derailleur that's not hanging straight: like excessive gap from the B screw, this will often confusingly show up in middle gears where the gap is greatest or chain deflection force is highest
- derailleur that's otherwise damaged: e.g., idler pulley whose bushing is totally shot so it deflects under certain tension
So: clean it (while moving the derailleur in and out), lightly oil the derailleur pivot points (people will yell about this but your bike is old enough that you can ignore them), blow a little air into the shifter while indexing it back and forth, check all shifter adjustments, eyeball the gear teeth and derailleur hanger and derailleur pivot. When in doubt, run new housing and cables the bike if it's been more than a couplefew years since you've done so. Then start fine-checking all the little details like derailleur hanger straightness.
posted by introp at 12:03 PM on February 9, 2021
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posted by computech_apolloniajames at 8:36 AM on February 8, 2021