Jim’s Tech Talk
By Jim Langley
This week’s main topic comes from a Tucson, Arizona roadie named Seth who asked for help with a frustrating chain drop issue. I offer some ideas for diagnosis and repair. After that, since everyone ought to have a custom cruiser for getting around, I’ll show you one – and with matching accessories.
“Query me this, expert wrench: I’m riding in the big ring, middle cog (11-speed drivetrain) and more often than not, when I shift the rear derailleur into a higher gear (i.e., smaller cog), the ring, not the cog, drops the chain toward the inside to the small ring.
If I shift the rear again, the ring moves back to the big ring. I’m on a cassette, chain and chainrings which are less than 6 months old. It happened on the old rings too. My mechanic can’t find it. I’ve never experienced the front jumping when the rear is shifting. The chain and cassette are SRAM, the crankset is Shimano. Any thoughts?”
Your auto shifting is an interesting issue, Seth. The first question I have is whether you tried a Shimano chain? You shouldn’t need to do that, but lately SRAM and Shimano have been engaging in a sort of chain war where they “improve” their chains – or some might think that the “improvements” are mostly intended to force you to use their chain or else suffer the consequences of bad shifting and strange glitches.
That’s mostly with their newest products, but still if I was working on your bike that’s something I would try. FYI: I gave this tip in RBR, but in case you didn’t read that column – my tip is to save old, used quick links and use them as “tools” for installing and testing new chains.
That way when you do a chain test like I’m recommending, you won’t be using the new quick link that came with the chain to size the chain or check the shifting. You use the old used quick link and when you’re satisfied that all is well, you can put on the “permanent” new quick link (most are 1 use only).
This is a long shot. But, if the chain isn’t the issue I would check the chainrings and crank carefully. Did by chance anyone ever take it apart to clean it and mistakenly put a ring on upside down? Or could there be incorrect spacing between the chainrings? Or… it’s pretty rare- especially with such new parts – but on bikes that get ridden a whole bunch, even large chainrings can get worn out and that lets them drop chains.
Let’s back up a minute. If you notice that the chain only drops at the same point on the crank revolution every time, then you should look for a bent or broken tooth or a bent section of chainring. That would act like a train track that moves to allow trains to change tracks.
If you put a piece of white cardboard on the floor so that you can see it behind the rings and front derailleur as you pedal by hand and if you can keep the bike from bouncing around in the repair stand or however you suspend it, you can sight for wobbles, bends and bad teeth.
With an adjustable wrench sized to just slip over the bent tooth or wobble in the ring, you can gently straighten things like this with a little careful tugging and trial and error (pull gently at first to learn how much force is needed to get the bend to straighten.) Note that if you have hollow chainrings, such as Shimano’s, don’t try bending them this way or you could ruin them.
Similarly, if the chain were to have a bad spot, a bend or a twist from something getting stuck or jammed at one time, that could cause it to come off, too. Like the chainring, too, if the chain is worn out, that could do it also.
Hopefully something here is helpful and you find the issue and fix it. It’s no fun dropping the chain and it can be dangerous. [Editor’s note: Seth wrote back telling me he has a Di2 front derailleur to which I added that he should carefully check its adjustment, too.]
If you have suggestions for Seth please leave a comment. Thank you.
State Bicycle Company Grateful Dead Klunker
I wouldn’t say I’m a Dead Head. But, in 1973 I did attend the Summer Jam concert in New York’s Watkins Glen Racetrack to see them – with 600,000 others! And, here at the University of California Santa Cruz resides the complete collection of Dead music, which the campus radio station KZSC 88.1 plays frequently and I enjoy.
So, I think State Bicycle’s collaboration with the Dead on a bicycle painted and stickered with the band’s dancing bears, skull and lightning bolts artwork would be a unique around town ride. State’s Grateful Dead Klunker comes in 2 colors and sells for $549.99. Only thing is, if you want one you probably better get an order in ASAP. To complement the bike they’ve come up with a Grateful Dead accessories and clothing collection, too.
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To see everything, truck on over to: https://www.statebicycle.com/collections/state-bicylce-co-x-the-grateful-dead.
Ride total: 9,976
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s cycling streak ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.
Rick Simpson says
When Triathletes migrate to 1x drivetrain systems they sometimes encounter chain-drop issues (especially with elliptical chainrings). These Chain-drop issues are often solved with a narrow-wide chainring.
Just an observation.
Ken Goldman says
I had a similar problem and suspected a bent derailleur hanger. It was a little out of line, but the real culprit turned out to be a bent rear derailleur cage.
Yes, all of the suggestions so far could solve the problem…hard to say which one so need to keep trying until one works.
One solution which has worked for me and has not yet been mentioned is to slightly adjust the cable length for both derailleurs, of course one at a time. Sometimes, just a VERY SLIGHT lengthening or shorting has worked. Sometimes, I have released the cable completely and started the adjustment process from scratch – including resetting the limit screws. It is very much a trial-and-error process, but if all of the other potential solutions fail to work, it may be worth a try.
One way to test to see if it is an issue with the cassette is to replace it and see if that solves the problem. Sometimes, changing out components is the only way to solve the problem or to eliminate potential solutions.
Stephen Turk says
I’m certainly not a Di2 expert, but my first question would be whether the front derailleur is actually moving and causing the front shift. Is Di2 somehow trying to auto-trim?
Steve Weeks says
This was my thought: that it’s an electronic shifting gremlin. I don’t see how else moving the rear derailleur could affect the front. Maybe it’s Quantum Mechanics: “Spooky action at a distance”!
Russ Marx says
RE: droped chain. Put the bike on a trainer and get someone to watch what happens, sometimes things only happen under load.
JOHN A JAUSS says
Late model recent (8000 ultragra, 9150 durace) rear derailleur have sycroshift(auto shifts front chaining when rear goes past a certain point up and down the cassette. My suggestion if this is the case would be to hook up to a computer and check for firmware updates. Ya need to know exactly what components are installed. Rereading the problem, the front derailleur CAN’T shift past the small ring if stop is adjusted correctly.
Johan Mokhtar says
As suggested by Stephen T, perhaps this is a Di2 Synchro shift problem.
Synchronized Shift is a function that automatically shifts the front derailleur when the rear derailleur is shifted, allowing the derailleurs to work together efficiently.
A bug in the system?
Dave Le Fevre says
Until I read that the front mech was Di2, my thought was that internal cables had crossed over in the down-tube. Thus an upchange on the rear mech (releasing some cable) would slacken the front mech cable, giving exactly this result.
Then I read that it was Di2. But I thought I’d post this reply anyway, just in case it helped somebody else.
Chris Homeyer says
Re: Watkins Glen
Man, I knew you looked familiar! Dead played after The Band, before the ABB (who were still reeling from death of Berry Oakley, though had added the incomparable Chuck Leavell on piano). I thought The Band put on the best show, followed by the Dead. We left before Jerry Garcia joined the ABB for an extended Mountain Jam.