Can a bad friction shift break a chain?
 

Broke a chain for the first time ever yesterday, thankfully close to home as the chain was damaged beyond repair after being immediately run over by a bus.

What happened was that I got stuck between shifts (friction shifting), as while trying to dial in a gear for a hill, I had to swerve to avoid a car door, leaving me having to go up a hill "between" gears. I didn't want to adjust it then, as I tend not to adjust rear shifting while having to put heavy load through the chain, but even on a short hill, the chain snapped entirely.


Can simply putting heavy load on a drivetrain with the rear derailleur not in line cause a chain breakage? And is this likely to have seriously damaged my rear derailleur?

Did it have a quick link and did it break there?

Yes, but it did not break at the master link. The broken link was missing the pin, and the plates appeared to be squeezed together but as the chain was immediately run over it's hard to say if this was the state of the chain immediately after the accident.

The chain also showed significant scraping on the side and several stiff links (zero indication of stiff links prior to the break) but once again, this might have been due to it being run over.

Also it was a relatively new chain (replaced last year, not too many road miles on it)

Yep. I think that there are a number of factors. As a chain is used it will be weaker, stretched, get looser/flexible. And a few bad shifts add up until it goes. If the chain is new it probably will break the hanger first, or the derailleur, or all three. I did it once when I was stupid and didn't setup for the terrain change on my mountain bike. Broke chain and made the derailleur and easy to pack two piece model. Steel frame so it bent the hanger. Thankfully the wheel (spokes) were okay.

Second stupid thing I did was toss out the B spring assembly and the clip, which I could use.

John

I haven't tested the RD yet, but it appears to be in-line just with the eyeball test of the pulley cage (I haven't re-chained the bike yet). Hopefully the chain was the extent of the damage.

'putting heavy load on a drivetrain with the rear derailleur not in line cause a chain breakage'. Yes...as is obviously the case :) Had it happen to me with a 1 x 10, trying to change up the block on a short sharp 7% climb (indexed). It's not that the indexing fail to do it's job, it was me - the rider - who was forcing it to do it under load. As you were using friction shifts your magin for error is narrower considering the nasty distraction of a car door. It's not uncommon. The outer plate on one of the chain links tore away from the pin...It's only happened the once. Before that I'd never broken a chain in over thirty years of pedal pushing.

As for the rear mech being damaged, well a visual inspection of it's postion on the hanger and the position of the hanger itself is in order. The only true test, if it looks ok to the naked eye, is to slap another chain through it, pop it in a work stand and cycle the gears...If a mech is seriously damaged it's usually pretty obvious to tell, normally because it out of shape (jockey wheel cage twisted, snapped body pins and the like).

Good to know- next time either stop or try to slack the chain a bit and correct the shift, then.

I'm rechaining it today (due to a bike boom-related lack of 6-7-8-speed chains in stock, using a 9-speed chain as a stopgap) so I'll check the RD functionality then. If not, well, there's an old Ofmega Premier at a local shop I've been looking at....

I've seen friction shifters break a few front derailleurs but I question whether they were installed correctly.

Bad technique shifting when forcing it can..

Yep. You can indeed break a chain with excessive load on or between gears. I've broken a chain (SRAM 11 speed) adjacent to the quick link on my first outting. Had I not had a spare master link, that 5 miles from civilization would have been a long walk. The pin extracted itself from a side plate. I just tossed the chain & have since sworn off SRAM as suspect quality at best.

My wife & I twisted a link 90 degrees from an errant shift on our 3x7 tandem. Everyything held together, but how a chain can twist & turn itself unside out is surprising.

Just because modern designs allow for shifting under power better than vintage stuff, but doesn't necessarily mean you should.

In any case, call it a lesson, install a new chain & carry on.
Good luck :thumb:

We have called this "soft pedaling" for decades. With good technique it only takes a couple of crank strokes to shift before reapplying power again. When stressed, distracted of just not paying attention any shift under power can damage the chain, indexed levers or not. Andy

Blowing a downshift under heavy uphill load is the classic way to break a chain. And a rear derailleur. And other things. Not all of which are bike parts.

--Shannon

Shifting on an incline:

Stay seated and surge for 2-3 pedal strokes then soft pedal and make your gear change. It doesn't use a lot of energy and it makes up for the resultant loss of momentum during the soft pedal/shift. Indexed shifting and & STI/Ergo has nearly eliminated this skill from most cyclist's tool box. It is possible to develop your skills to do this standing (using brake/shifters) but it requires more skill than the first method I listed. The best cyclists I've ever ridden with knew exactly when, where and how to shift with minimal loss (if any) of momentum. It's truly an art.

To answer the original question, yes a poor rear shift can break a chain. It's basically using one or two of the freewheel/cassette teeth as a cutting tool on the underside of the chain while it's at an angle.

Edit: is it possible that the odd forces involved with the chain tension suddenly snapping under load did something odd to the BB? There does seem to be more flex when testing the pedals than normal.
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I'm checking the stays for damage as well though this seems unlikely.



Unfortunately the cage has possibly been bent. I'm getting ghost shifts and a rattling feeling similar to FD chain rub only when pedaling.

The cage is OK with the eyeball test, and seems to function alright when backpedaling (and oddly enough, when hand cranking with the bike in a stand) but seems to have a minor amount of play (roll) to the cage- without a known good derailleur I don't know how normal this is. It's also possible it just doesn't like the 9 speed chain.

LBS time, then, as I think this is beyond my ability to diagnose.

Hey, good news, replacing the 9s chain with a 8s chain fixed the issue. Not sure why the drive chain hated the 9s chain so much, but hey.

The drivetrain was insulted and in terror of being replaced, so it threw a tantrum.

More seriously, 9-speed and above chains are often noisy on 8-speed and below drivetrains. My rule has always been to use speed-specific chains on 9 and above, and 8-speed chains on 8 and below.

--Shannon

You do that for a rear cog shift. However, making a front chainring change requires a surge and soft pedal. IE an unexpected pitch in the road that requires a rapid big to little change or a little to big change (while still on the climb) to crest and motor away while everyone else is still climbing behind you.

The key to the surge is not to just accomplish the shift, it's to minimize the loss of momentum that can create a gap between you and someone else (or create a gap). Obviously, my take on this comes from being a bike racer but as mentioned, front shifts on an incline require a pedal surge if you want them to go smoothly. This is especially true with a compact/sub compact cranks because the 16T difference between chainrings means a rear shift will probably have to happen as well.

A basic rule of thumb is "if it's making noise/not shifting for longer than a second, you're doing something wrong".

Funnily enough, when using modern chains designed for indexed shifting systems, the chain for 6, 7 and 8 speed are the same. So if you are using an 8 speed chain on a 7 speed drivetrain, you are actually using a 7 speed chain without knowing it!

I've never tried, but I suspect using a chain built for fewer speeds than the cassette (like an 8 speed chain on a 10 speed cassette), the wider chain will always be clattering against the gears it is not in. I am currently using a 9 sp. chain and cassette with a 10 sp. front derailleur, and it seems like the chain wants to rub the derailleur unless I am very careful with the position of the shifter.

You were really abusing your equipment and i protest it failed. That's to be expected when not shifting correctly into gear and then riding har without positive engagement of the chain and sprocket. You're really lucky nothing else was damage and that you didn't crash.

Cheers