Rear hanger snapped off twice

[bikerdan]

My rear hanger snapped off a week ago. Rode up the short 20% ramp from my garage in smallest gear, turned left shifted up several gears and rear hanger snapped off

No big deal I thought. Ordered new rear hanger and new chain to be safe. Ran through all the gears on the stand. Short flat pedal to also check all the gears. All fine. So yesterday went to ride up the 20% ramp from the garage and new rear hanger snaps off

And I can't figure out what's caused it. Didn't hear any tinking on the spokes...chain was sized big/small and jockey wheels in line which should be perfect with an 12-25 cassette

Rear derailleur cage is bent will need to be replaced. Rear drop out has a crack in it but looks just like the clear coat can't tell. Any options on the drop out from the pictures?

So think my possible options are
1) New cage for di2 mech
2) New di2 rear mech
3) New frame and new rear mech

I think 2) is probably safest. But having not understood why it's happened twice and that crack in the drop out, I'm hesitating to go that way

[NiFTY]

Assuming smallest gear means easiest ie small front biggest rear. Presumably before the hanger snapped the setup had worked without issue and nothing had been adjusted recently. Ie derailleur limits, cassette size, crank/chainline.

Hanger breaking normally indicates the drivetrain stalling. Did the chain fall off between the cassette and spokes? Are the jockey wheels in good condition - did the chain slip off the inside of the jockeys and get caught in the cage. Is there enough clearance between top jockey and cassette? Stiff link in chain?

[bikerdan]

Thanks for the suggestions. Yeah by smallest I meant 36x25

When it exploded the second time chain wasn't between the sprockets and spokes and limit screws/setup hadn't changed.

I checked the chain which was also new and there were no stiff links or plates hanging out

So from your suggestions I'm guessing jockey wheels. I took them out and regrease them a while back and there was also a sound I couldn't get rid of. Also when spin the cranks on the stand the cranks would keep spinning for a bit

I guess safest bet would be new rear mech. Although I'd hope a new cage and jockey wheels would also work

[Gary71]

So let’s back up a bit……, did the 2nd hanger come from the supplier of the first and how long between bike purchase and 2nd hanger? I am wondering if both hangers were from the same production batch and the material was compromised / contaminated and couldn’t stand up to the intended purpose.
Let’s face it - the rear hanger should be able to hold loads from any combination of gears and Greipel loads of torque……., it’s a bike, ride it like you stole it.
I get frustrated with the argument the hangers are supposed to fail to protect the bike and the components. I call bullshit on that. Your rearD usually ends up gnarled in the rear spokes with your chain, nuts planted into the stem, followed by a face plant. How is that saving anything?
After recovery you are up for a new rear wheel, rear derailleur, chain and hanger……, only to be hesitant to give it the full beans the next time up the hill.
Cast your mind back 40 years when all frames were made out of steel. I cannot recall a single hanger being snapped/broken. Post crash or otherwise. Now I get that a carbon hanger is at more risk and less mailable than it’s steel counterpart, but surely there are engineers out there that could 3D print a titanium, steel incorporated as part of the design? Or just over engineer the carbon rear hanger
The move to disc frames also shifts the design and hanger strength integrity back onto the face of the bike designers so build it like its a tank. I would prefer to see my rear derailleur be ground to toast and have to replace it then all of the above.
…….., maybe I’m just an ignorant Luddite
Rant over

[bikerdan]

Frame is about 7-8 years old. Replacement hanger was from Look and got it only when the other broke. So can't be bad batch

My current feeling is I screwed up twice. When I replaced the chain/cassette early this year something wasn't 100% right. But as I was mainly using another bike I neglected to really chase it down

Second break I assume was from damage to the rear mech from the first break even though it shifted fine on the stand and on a short flat run

But next time out up the ramp from my garage I'm going to be totally paranoid

[rpowell]

couple areas i would check
1. look for any bent teeth on your cassette or chainrings. people don't usually look but a bent tooth could put large loads on the hanger.
2. check the alignment of the hanger.
3. confirm no stiff links in the chain.
4. check to confirm the cassette cogs dont wiggle or are otherwise loose.
5. confirm that your chain isnt too short. did you put a larger cassette on?
6. how close is your upper pulley to the cassette? did you adjust your b screw.

thats my basic process for debugging. these should all be quick checks.

[Sockman]

I'd bet a good sun of money on the chain length, maybe coupled with the B screw.

Hard to do now, but if you shift into the 53/11 (or equivalent largest gear) your jockey wheels should be vertically aligned as per shimanos set up guide.

[jih]

Might not be a factor, but 36x25 is quite a high gear for a 20% grade. Are you really wrestling the bike up that or are you a strong enough rider that you can ride normally?

If you're wrestling the bike, that could be flexing things just enough that something else goes wrong

[kode54]

The OP changed cassette and chain…chainrings original? It’s possible that the chain jumped off the front chainring while powering up 20% grade (with more torque), jumped over the teeth on the front and causing undue force in rear cassette thus, breaking the hanger. Just a thought.

[tarmackev]

Sounds like a dodgy hanger to me.
I'd buy another and repeat the process. Perhaps get a bike shop to change it just so you have some come back. When a hanger breaks there's generally a noticable mechanicle fault of some kind before it goes "snap". If it all rides as normal and just silently brakes i'd guess faulty.

[WorkonSunday]

is your rear wheel coasting freely sometimes freehub malfunction will cause the chain to keep moving forward while pedalsstopped then bottom half of the chain get the tension and the only sack in the system is rear mceh being snaped backward

[bikerdan]

Thanks for all the suggestions. Took my time and checked everything out.

I'm now pretty sure it failed the first time due to chain being too short and b-screw adjustment. I now vaguely remember changing the b-screw on the stand to see what difference it made to the noise I was experiencing from new cassette and chain. I guess noise was actually short chain and then not putting the b-screw back caused the fail

Second fail probably mixture of twisted cage on the derailleur and b-screw still not corrected

Ended up with new mech, chain, freehub and fully adjusted. Gears felt silky smooth again and ride up the ramp was fine

[kode54]

Good you swapped out everything. I dropped a chain years ago and had issues thereafter. Turned out that the chain had a kink in it and didn’t lay flat…thus creating poor shifting and occasional chain drops and possibly of snapping the rear derailleur.