[Closed] Keep bending rear mechs

You sure it's not the hanger that's getting bent?

I don't think so because the LBT (Local Bike Technician) says its the deraileur and also when it happened the other 2 times in the past the LBT changed the derailer only and the problem was solved (until the bending returned very soon afterwards) without changing the hanger.

if you think it's because of when you're putting the bike on the floor to open gates and you're doing that gear-side down, stop doing that

It's just that this has never happened before with the 2x10 setup and I used to put it gear-side down regularly.

Is it possible that, due to the larger cassette on the 1x10, the deraileur could now be in a position where it's more likely to get bent when the bike is put gear-side down ?

putting a bike gear-side down is (old fashioned term) poor practice, stop doing it anyway, a beneficial side effect might be fewer bent rear mechs 🙂

There is no excuse for placing a bike derailleur side down, you are being mechanically unsympathetic to a very sensitive precision design, in a previous life I was a skills coach/guide and seeing this used to boil my piss.

Singlespeed - the answer to most of life's problems

Right mech for the size?
Leaving it fully extended and laying it down will leave it open to more leverage than a smaller 2x situation.
Is the chain lenght right? How much extension is left at 42t in the mech?

I was going to say is chain length right and has the mech got the capacity to cover that 42t cog? Is it Shimano or Sram? If the former, have you got a goatlink / radr cage or long b screw?

And what's so hard about putting the bike down non derailleur side?!

It takes (ime) a fair effort to bend a mech..
are they actually twisted, bent, knackered or does the shifting just go rubbish??
Have you checked the chain?? Is there a twisted link that's catching the cage?
Do you try to shift gears when peddling hard?

I'd be inclined to try another bike shop with a hanger alignment tool before buying a new mech (unless you've got another broken one at the mo)

Are limits set correctly? Sometimes they're JUST able to reach their limits, but give em another half of quarter turn to ensure the chain is adequately seated.

Assuming you're full sus, let all the air out of your shock/remove the spring, and get someone to fully compress the suspension while you check if there's any slack in the chain. From expensive experience on a mate's bike, some designs have far more chain growth/shortening than you'd expect.

Given that you have (I seem to recall) a full sus, I'd say chain length is maybe too short.

I have to say though, given your propensity for knackering almost everything on your bike, maybe a couple of the STW regulars should go for a ride with you so they can report back on just why this is so..?!

I kept bending mechs when I changed to a full suss but it took a slow, small jump for me to put 2 and 2 together. It only happened when the shock was at almost full compression and I'd dropped a load of psi as I was just doing dh runs. Do as coatesy says to check.

If the chain is too short are you sure your LBT knows what he or she is doing? Maybe you should get a Local Good Bike Technician (LGBT) instead? Always good to diversify IMO.

larger expander cog - chain growth - mechs that bend easier than they used to.....

Probably one, or all of these I reckon.

3 mechs in 7 months? I've the same mech running 1x10 on my hardtail (my only MTB) after 3 years! Do Coatsey's check. Davosaurusrex's suggestion might be a bit too far though 😉

If the chain is too short are you sure your LBT knows what he or she is doing?

It's pretty tricky to bend a rear mech without bending the hanger first.
So my guess is he's fitted a new mech (which he has in stock), and got it to work and tweaked the bent hanger back into some sort of shape that allows the gears to work. As i'd guess he doesn't have the hanger in stock.

Bent hangers loose a lot of strength, so next time you get out for a ride, ooooo. You need a new mech, you've bent it again.

Try get a [u]CNC[/u] machined hanger next time, that won't bend. (A consequence to this is sharper gear shifting and eventually the mech taking the beating if the hanger doesn't crack).

as mentioned multiple times; right type of mech for the cassette(GS, SGS, GoatLink)? chain length vs. chain growth? has the hanger been replaced or just bent back each time ?

LBT (Local Bike Technician)...

Given the previous mechanical history of the OP I'm taking a keen interest in this. My advice would be to remove LBT from the equation entirely before making any more expensive decisions. I'd swallow the cost and inconvenience and go to a reputable bike shop.

The first port of call has to be the mech hanger, which should be replaced and correctly torqued. The only other issue that I can think of is that the mech cage is colliding with the spokes of the rear wheel, either due to a foreign object being caught in the spokes or due to flex in the wheel - the latter could be fixed for less than twenty quid by a decent bike shop.

Also, dropping the bike on ground driveside downwards or leaning the bike in such a way as to put weight on the mech is an extremely bad idea, regardless of whether it's nine speed or twelve speed.

I would guess the chain is too short and it's bending the mech under full compression - did you lengthen the chain when moving to 11-42?

I would guess the chain is too short and it's bending the mech under full compression - did [s]you[/s]the LBT lengthen the chain when moving to 11-42?

FTFY

I've done some bad things to bikes. Once bent a frame by being in big ring/big sprocket on a too short chain. Also had a chain jam in the jockey wheel when winching up a big steep hill which ripped the mech off the bike and dragged it around the wheel - the hanger snapped.. I'm still using the same mech I've had since 2007 that was in both these incidents - it's still fine. Also once ovalised a freehub body which meant instant fixie conversion, and the the whole force of my momentum went through the lower chain. Still using that mech too.

So mechs are quite strong (well 9sp ones anway) so something is badly out of whack. For your mechanic to simply swap them and send you on your way is pretty poor show imo.

Also, dropping the bike on ground driveside downwards or leaning the bike in such a way as to put weight on the mech is an extremely bad idea, regardless of whether it's nine speed or twelve speed.

I've also dropped and crashed bikes countless times, and bent plenty of hangars slightly. And still never bent a mech.

Frivolous answer: Three mechs in 6 months is not excessive. One mate was going through one every couple of rides last year. Just rock impacts, no incorrect adjustment involved.
Carries a spare mech all the time now. At least he never has to worry about jockey-wheels needing replacing 😛

Serious answer: The "growth" under suspension compression is the most obvious thing to check first.

Are you certain that it is a bent RD, and not just poor shifting that is leading you to suspect a bent RD? Other options for poor shifting are a contaminated gear cable and of course a bent hanger.

As others have said the RD is a pretty robust device (although I bent one when it went into my back wheel once - forget poor shifting, this one was obviously out by an inch!). If you asked for a replacement, then it's not surprising that's what they would do - and presumably replace the cable too.