couple of issues on a ride tonight, advice please

clackadelic

so. on a ride tonight couple of hours out enjoying the warmer (and drier) weather on the local byways when the rear mech drop-out fails and I end up crunching the gears and being stranded 18 miles from home. Sucky I know.

first, is this common? I've probably done 500 or so miles of mixed terrain but have never given the rear mech any kind of whack, seems to be shitty luck if nothing else.

secondly, I'm riding a 2012 Marin Palisades Trail 29er which has a SRAM X7 derailleur. In the process of the drop-out breaking, also broken are the two guide wheels and the cage arm is probably bent beyond straightening. (I expect no longer exact actuation), So it is probably cheaper just to replace the whole mech which might give rise to an easy upgrade. Can anyone tell me if I have the long or medium cage currently? I would guess it is the long cage but any paperwork with the bike is long gong and I can't find any info online.

thirdly, to add insult to injury I have only just replace the KMC X10 chain and 11-36 cassette so am not in an immediate rush to spunk unnecessary cash to replace those.

All advice gratefully received.

bob6397

It's not that common - but (slightly ironically in this case) the mech hanger - which I think is what you are referring to - is designed to break in the case of an impact on the derailleur - the mech hanger is £10-£20 to fix and your mech could be a whole lot more than that...

From the pics that looks like a long-cage mech but you can actually work out which one you need by knowing the ranges on the chainrings and the cassette and taking that to work out total chain growth and therefore which cage you need (It is simpler than I make it sound).

With the cassette and chain, check that neither got bent when your mech ended up in your wheel and if they aren't then they should be fine.. If they are then I would replace them as it will increase chain wear/increase likeliness of the chain breaking if they are bent/damaged..

bob6397

Antm81

As Bob said the mech hanger is sacrificial, although not to protect the mech itself, it's designed to avoid damage to the frame. Sounds like a new hanger and rear mech would be the simplest solution.

As for the length of the cage, you are looking at difference between the biggest and smallest chainrings added to the difference between the biggest and smallest cogs on the cassette. This will give the capacity you require from the mech. The mechs should then have a max capacity listed for each size cage. As a general rule though, if you have a 3x setup you'll need long cage but a med cage may be ok on a 2x.

As for the cassette and chain, I'd leave them be if there's no visible damage which will be pretty obvious.

cooldad

If the hanger snapped just after you replaced the chain, you probably made it too short.

Check before riding or the new stuff could follow the old.

The Rookie

cooldad wrote:

If the hanger snapped just after you replaced the chain, you probably made it too short.

This, a chain too short (or even shorter than the one you took off if the B-screw isn't adjusted for the new tension) can pull the upper jockey wheel into the cassette, result as per your experience, or did you replace an 11-34 cassette with an 11-36 and not adjust chain length and B-screw as required - the same result would occur.

clackadelic

Thanks for the replies. I swapped like for like on the chain and the cassette so don't think that was likely the issue. Especially as I had recently had a workshop course showing me how to change them! Looks like they are ok but I'll double check to see how smoothly they run after the new hanger and mech arrive and make a final decision.

Funny, I used to think running motorcycles was expensive!

Lastly for info, SRAM have a chart which is downloadable from their website which shows compatibility amongst components. Handy, took me a while to get my head around the colour code system though.

The Rookie

Did you measure the chain on fitment, or just compare to the old one? Always best to do it yourself just in case you'd managed to get away with a mis sized chain by luck!