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Broken 105 Di2 Rear Derailleur

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Broken 105 Di2 Rear Derailleur

Old 02-19-24, 05:59 PM
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Broken 105 Di2 Rear Derailleur

Before I tell you how I think it broke, anyone have their derailleur break in this area before? It broke on the 4th ever ride so basically brand new. This was a costly break but the bike is all fixed.

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Old 02-19-24, 06:23 PM
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Not add specific to any particular RD, but it's consistent with having been snagged in a spoke and torn off backward. That or some other form of crash damage.

If you're looking for a definite answer, look for clues like scratches or other marks elsewhere on the body, or possibly a bent spoke.

Often these things happen in two stages, where a fall or crash bends the hanger inward. This c allows the RD to overshift into the wheel the next time you shiftt to low.
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Old 02-19-24, 07:13 PM
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It broke like that, because that part is made of plastic.
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Old 02-19-24, 07:54 PM
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Originally Posted by Kontact
It broke like that, because that part is made of plastic.
Yes, the specific mode is because the weakest (plastic) part broke, but mode of failure is different than cause of failure.

Something happened to cause it to snap, and that's what the OP needs to consider if he doesn't want a repeat.
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Old 02-19-24, 08:33 PM
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Originally Posted by FBinNY
Yes, the specific mode is because the weakest (plastic) part broke, but mode of failure is different than cause of failure.

Something happened to cause it to snap, and that's what the OP needs to consider if he doesn't want a repeat.
Gee, I never thought of that. Thank you FBinNY!

I wonder what minor adjustment the OP will find that will prevent the next $200 plastic derailleur from being destroyed? Maybe he'll identify a thin, rubbery derailleur hanger as the culprit, and then he can pray really hard that nothing bumps it again (since there is nothing else to do).
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Old 02-19-24, 08:58 PM
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Originally Posted by Kontact
Gee, I never thought of that. Thank you FBinNY!

I wonder what minor adjustment the OP will find that will prevent the next $200 plastic derailleur from being destroyed?....
No need for the sarcasm. We basically agree, and I'm no more a fan of overpriced disposable components than you are.

But, I prefer to assume the OP is looking for more than a general indictment of high end plastic RDs. As for minor adjustments that might factor, how about inner limit and/or trim? (which you know as well as I do)

However, it would be helpful if the OP were more forthcoming. Without specifics, we can only throw stuff against the wall hoping something sticks.

Last edited by FBinNY; 02-19-24 at 09:01 PM.
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Old 02-19-24, 11:16 PM
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Originally Posted by FBinNY
No need for the sarcasm. We basically agree, and I'm no more a fan of overpriced disposable components than you are.

But, I prefer to assume the OP is looking for more than a general indictment of high end plastic RDs. As for minor adjustments that might factor, how about inner limit and/or trim? (which you know as well as I do)

However, it would be helpful if the OP were more forthcoming. Without specifics, we can only throw stuff against the wall hoping something sticks.
If the L trim screw isn't tight enough on Di2, will you shift into the spokes if you push the button extra hard?
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Old 02-19-24, 11:28 PM
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It comes with a two year warranty, so if JRA, get the bike shop to handle it (or send it to Shimano yourself).
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Old 02-20-24, 04:28 AM
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No idea. However, since I've got 105 Di2 myself I'll be interested to hear the end of the story. Mines done a little over 2,000 miles now.
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Old 02-20-24, 06:15 AM
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Originally Posted by Polaris OBark
It comes with a two year warranty, so if JRA, get the bike shop to handle it (or send it to Shimano yourself).
Pretty sure that wouldn’t be covered by the warranty.
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Old 02-20-24, 06:43 AM
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No more replies from the OP, I see. We'll never know the end of this story?

Originally Posted by Kontact
If the L trim screw isn't tight enough on Di2, will you shift into the spokes if you push the button extra hard?
It's just a click button, so "extra hard" won't matter. Holding the button down usually causes a multiple-cog shift, but that won't go past the end cogs, of course.

I suppose the trim screws are only for an incorrect rear derailleur shifting setup -- with the chain way off center from the cog, or even off by a full shift.
Centering the chain correctly is very easy if you just follow the dealer manual:
While turning the front chainwheel,
operate shifting switch [X] to move the
guide pulley toward the inside until the
chain touches the 4th sprocket and
makes a slight noise.

Next, operate shifting switch [Y] 4 times
to move the guide pulley toward the
outside by 4 steps to the target position.

~~~
Limit screws. The low limit is simple, but the high limit is a bit unusual, compared to mechanical shifting. (Di2 "over shifts", then moves back a bit after a brief pause.)

Shift the rear derailleur to the largest
sprocket, and then tighten the low limit
stopper bolt until it just touches the left
link.
If it is tightened too much, the motor
will detect a problem and gear shifting
will not operate correctly.
...
Shift to the smallest sprocket, and then
tighten the top-side stopper bolt until it
touches the left link at the position
where the rear derailleur stops.
From this position, turn the top-side
stopper bolt counterclockwise one turn
so that an over-stroke allowance can
always be maintained.

Last edited by rm -rf; 02-20-24 at 06:50 AM.
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Old 02-20-24, 06:55 AM
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Originally Posted by smd4
Pretty sure that wouldn’t be covered by the warranty.
Don't know unless you try
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Old 02-20-24, 07:19 AM
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Originally Posted by dedhed
Don't know unless you try
Of course I know. Warranties--Shimano's included--usually only cover defects in materials or workmanship. This damager is neither.
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Old 02-20-24, 07:26 AM
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Hi all!

Great responses, as expected from this forum.

No warranties here because it's definitely not a defect in workmanship or material (other than it is plastic, I guess).

I was curious if any had this happen before that wasn't related to a crash. That's the reason why I posted (and to also state be careful).

I believe what happened (though I don't know for sure because it all happened so fast) is I slipped trying to clip into my pedals and while the pedal was oscillating closest to the derailleur. As a result of the slip, my show banged into the derailleur, thereby breaking it. I didn't realize it at the time. I thought my chain just slipped or the derailleur somehow get misaligned. But a quick pit stop quickly made the situation known. Luckily, I was not far from home so just coasted/walked home. Kind of like the walk of shame?

Luckily, I live in an area w/ a lot of good bike shops so I was able to find one that had 1 of these in stock and got it fixed, but not w/o some stress. Apparently, the shop didn't realize you have to repair the shifters (they call it switches) to the derailleur. They thought it would automatically work. I had to stop in and google the situation for them......Next time, I'll do it myself.

So what did I learn? I'm left footed so I click in my 2nd foot from the right side. I will start to learn to clip my 2nd from the left side.
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Old 02-20-24, 07:48 AM
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Originally Posted by rm -rf
It's just a click button, so "extra hard" won't matter. Holding the button down usually causes a multiple-cog shift, but that won't go past the end cogs, of course.
I was being facetious.
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Old 02-20-24, 07:57 AM
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Originally Posted by howaboutme
Hi all!

Great responses, as expected from this forum.

No warranties here because it's definitely not a defect in workmanship or material (other than it is plastic, I guess).

I was curious if any had this happen before that wasn't related to a crash. That's the reason why I posted (and to also state be careful).

I believe what happened (though I don't know for sure because it all happened so fast) is I slipped trying to clip into my pedals and while the pedal was oscillating closest to the derailleur. As a result of the slip, my show banged into the derailleur, thereby breaking it. I didn't realize it at the time. I thought my chain just slipped or the derailleur somehow get misaligned. But a quick pit stop quickly made the situation known. Luckily, I was not far from home so just coasted/walked home. Kind of like the walk of shame?

Luckily, I live in an area w/ a lot of good bike shops so I was able to find one that had 1 of these in stock and got it fixed, but not w/o some stress. Apparently, the shop didn't realize you have to repair the shifters (they call it switches) to the derailleur. They thought it would automatically work. I had to stop in and google the situation for them......Next time, I'll do it myself.

So what did I learn? I'm left footed so I click in my 2nd foot from the right side. I will start to learn to clip my 2nd from the left side.
I can understand clipping in that way if you’re in a “drive on the right” country. Right foot on the kerb at lights.
What I can’t understand is my son doing it. I might have to start tying one leg behind his back or whatever it was the Victorians did with left-handed children because they thought it was the devil’s work.

Hell of a random way to break an expensive component. Very unlucky.
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Old 02-20-24, 08:01 AM
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Originally Posted by howaboutme
I believe what happened (though I don't know for sure because it all happened so fast) is I slipped trying to clip into my pedals and while the pedal was oscillating closest to the derailleur. As a result of the slip, my show banged into the derailleur, thereby breaking it.


So what did I learn? I'm left footed so I click in my 2nd foot from the right side. I will start to learn to clip my 2nd from the left side.
Rather than change which foot you clip in first, consider how you’re clipping in. If I understand you correctly, you are clipping your right foot in with the pedal in the rearward most position. This seems odd to me. Though maybe this is common for others.

I also clip left side first, but rotate the cranks so the right pedal is towards the front and then clip in. This way the force for clipping in is applied the same way you do the power stroke.

it just sounds very awkward clipping in with the pedal to the rear.
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Old 02-20-24, 08:12 AM
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I think what happened is that I tend to let my drive foot (left in this case) get started, which then has my right crank at Noon. I start the clip in process at Noon and if I don't pay attention and can't get the clip in process right, my foot slips backwards. So it's not because I clip at the 9 o clock position. It's slipping from the Noon ish position backwards. Again, super unlucky this one time and hopefully a fluke. I will be super careful next time and will likely not worry about trying to clip on on the first attempt and just soft pedal w/ right shoe sitting on the pedal and then when I'm out of the intersection and feel less stress, then clip in.
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Old 02-20-24, 08:21 AM
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are you right leg dominant ? do you kick a ball with right leg / foot ? is your right leg stronger ? when you mount the bike do you plant left leg / foot on the ground and swing right leg up and over the bike (top tube) ? do you ride a motorcycle ?

if answer to above is ‘yes’ - typically you would clip in with right shoe first
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Old 02-20-24, 08:23 AM
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Am I missing something? Who clips in on the up (back) side of the stroke?

It seems totally illogical trying to press down to clip there. I've been riding clipless since the beginning, including with fixed gear, and can't remember ever clipping in other than during the power stroke.

BTW -- UK or USA shouldn't matter. Any urban cyclist tends to become ambidextrous as they're forced to adapt to various situations.

Note, if the OP typo'ed and meant he tried to unclip it makes more sense.

Last edited by FBinNY; 02-20-24 at 09:00 AM.
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Old 02-20-24, 08:27 AM
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Originally Posted by t2p
are you right leg dominant ? do you kick a ball with right leg / foot ? is your right leg stronger ? when you mount the bike do you plant left leg / foot on the ground and swing right leg up and over the bike (top tube) ? do you ride a motorcycle ?

if answer to above is ‘yes’ - typically you would clip in with right shoe first
Yeah, I mentioned this already, above. I am left footed.

Originally Posted by FBinNY
Am I missing something? Who clips in on the up (back) side of the stroke?

It seems totally illogical trying to press down to clip in there. I've been riding clipless since the beginning, including with fixed gear, and can't remember ever clipping in other than during the power stroke.

BTW -- UK or USA shouldn't matter. Any urban cyclist tends to become ambidextrous as they're forced to adapt to various situations.

Note, if the OP typo'ed and meant he tried to unclip it makes more sense.
I explained this above. I wasn't trying to clip in on the upstroke.
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Old 02-20-24, 08:34 AM
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Originally Posted by howaboutme
Yeah, I mentioned this already, above. I am left footed.



I explained this above. I wasn't trying to clip in on the upstroke.
Time overlap ----- I'm a slow typist posting from my cell phone.

Now it makes sense.

For the future, if you fail to engage properly, simply press forward to keep the toe engaged, then align and press down as you begin the power stroke.
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Old 02-20-24, 08:45 AM
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Originally Posted by FBinNY
Time overlap ----- I'm a slow typist posting from my cell phone.

Now it makes sense.

For the future, if you fail to engage properly, simply press forward to keep the toe engaged, then align and press down as you begin the power stroke.
Yes, total fluke. Thanks for the suggestion!
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Old 02-20-24, 08:57 AM
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Originally Posted by Polaris OBark
It comes with a two year warranty, so if JRA, get the bike shop to handle it (or send it to Shimano yourself).
Originally Posted by smd4
Pretty sure that wouldn’t be covered by the warranty.
Do you know what "JRA" stands for?
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Old 02-20-24, 09:10 AM
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Originally Posted by Koyote
Do you know what "JRA" stands for?
I don't. What does it mean?
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