Ugly GRX RD failure...

[572cv]

These are helpful observations. At least in the aftermath, the cage was certainly bent, and if it had been dropped on its side as a rental, its reasonable to suspect the hanger too. With such a long cage, it would be easy for it to have been bent somewhat before my friend picked it up. Spoonrobot’s thoughts about maintenance (filthy cage, mismatched parts) suggest that a bent cage, or other issue could easily and perhaps likely be overlooked. Rental maintained for quick turnaround, not much else. My pal will follow up when he takes the bike back today.

Thanks everyone

[Louis]

I'm sure rental bike are used and abused in ways that we'd never dream of doing with our stuff. And much of it probably isn't reported to the rental shop, so unless they inspect everything very closely when it comes in or before it goes out, who knows what sort of JRA failure is waiting to happen.

Knowing nothing else, I'd blame it on the fact that it was a rental.

[oldpotatoe]

Originally Posted by EB

Easy to blame Shimano but I agree that's either a limit screw that was set wrong, a bent hanger, or even a combo of the two.

Gee, pretty funny...if this was a Campagnolo rear der the pitchforks and torches would be out and on the way to Campagnolo, NA...

Maybe the rear der aillleur just, ya know, broke(??)

[mjf]

Originally Posted by oldpotatoe

Gee, pretty funny...if this was a Campagnolo rear der the pitchforks and torches would be out and on the way to Campagnolo, NA...

Maybe the rear der aillleur just, ya know, broke(??)

😂

Definitely agreed

[LJohnny]

Is the back wheel itself coming out of the axle? It looks off center with respect to the rear axle center. Maybe the angle of the picture/lense distortion, but seems off to me.

[prototoast]

Originally Posted by oldpotatoe

Gee, pretty funny...if this was a Campagnolo rear der the pitchforks and torches would be out and on the way to Campagnolo, NA...

Maybe the rear der aillleur just, ya know, broke(??)

As a frequent Campagnolo critic, I want to emphasize my complaints are largely focused on their shifters and cranksets. Their derailleurs are just fine.

[Hank Scorpio]

Looking at picture 2 there are definitely scratches in the lower pivot of the body although none on the cage. Can't tell how it would get scratched so heavily in that one location from a fall and nowhere else. Maybe if it happened while it was on the big cog in the back that kept the cage off the ground?

[dddd]

Derailers get torqued rearward from spoke contact often enough, but another failure mode with a similar outcome is from the chain seemingly getting derailed off of the top pulley and jamming, then typically "lacerating" or "chain-sawing" the cage plate at that location to some visible degree as evidence.

In this latter scenario, it's not torque being applied to the derailer cage by the spokes that does the damage, but chain tension that pulls the derailer cage around with the rotating cassette (seemingly the cause here because the OP mentioned the rider not needing low gear when this occurred).

As for a too-tight chain, are there any derailers from the past 30 years which can't move fully out of the way of a full-tight chain[?] (not to say that a too-short chain won't cause damage to any number of other parts, including the frame, and which could perhaps damage the derailer itself as a consequence of other parts failing).

[gfk_velo]

Originally Posted by oldpotatoe

Gee, pretty funny...if this was a Campagnolo rear der the pitchforks and torches would be out and on the way to Campagnolo, NA...

Maybe the rear der aillleur just, ya know, broke(??)

At the Service Centres, we're used to it ... imagine if all those cranks had been Campag - Jeez. Or even, the same %age (before anyone says it ...)

[gfk_velo]

Originally Posted by prototoast

As a frequent Campagnolo critic, I want to emphasize my complaints are largely focused on their shifters and cranksets. Their derailleurs are just fine.

At least, with very few exceptions, the cranksets stay in one piece and the shifters are to some extent serviceable & available as body only and/or L / R units complete, so youre not buying a new pair every time ...

[Black Dog]

Originally Posted by gfk_velo

At least, with very few exceptions, the cranksets stay in one piece and the shifters are to some extent serviceable & available as body only and/or L / R units complete, so youre not buying a new pair every time ...

Don’t spoil all the haters fun with facts. 😉

[Davist]

That looks like a regular derailleur failure to me, not a particularly ugly one, the longer the cage the more leverage it has, so.. begging the question, what's a "pretty" derailleur failure look like? sorry it ruined the ride!

[572cv]

Originally Posted by Davist

That looks like a regular derailleur failure to me, not a particularly ugly one, the longer the cage the more leverage it has, so.. begging the question, what's a "pretty" derailleur failure look like? sorry it ruined the ride!

Circling back to this as I see it is still active. The bike was returned (O2 Cycles, Bordeaux) on my friend's departure. He will let me know the denouement. Of some concern is not being here to further discuss, and the large deposit being held by O2, and some sense that O2 might decide he was to blame.

I agree that there is no pretty derailleur failure! This just looked very bad, with plastic blown out and all!

Again, thanks for all the observations.

[Bici-Sonora]

I agree, over 3 years, my GRX 2x group has been the most durable and robust shifting group I've ever used. Also, it's on my gravel-travel bike and I've not treated it delicately. This failure looks to me like some combo of improper set up, maintenance, and rental bike abuse or neglect.

Originally Posted by 2metalhips

I've been using GRX for 4 years on a Cutthroat in all kinds of conditions, mud, snow, ice, frozen mud. Never missed a shift and bombproof.

[dddd]

From my off-roading experience, even the tiniest of twigs can derail the chain off of one of the pulleys, leading to carnage.

Even a small piece of paper or plastic wrap floating in the breeze, or a small stone bouncing up from the roadway, could similarly inflict mayhen on the chain's intended running path.

I don't see where the renter has cause to say that the rider was necessarily at fault here, rather it's the crap-shoot of riding in the real world that seems probably to blame.

I have seen loose limit screws and pulley bolts derail chains though, which I would say is traceable to some lack of proper bike setup.

Without the derailer here to do post-mortem on, the cause seemingly can't be determined, but with the cable housing looking the way it does, possibly it snagged violently on something, especially as the chain seems to have been forced beyond low gear. Hopefully the frame is ok.

Lastly, it might be worthwhile to read the rental contract(?).