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My rear derailleur likes my spokes alot...

DevyheadDevyhead Posts: 16
edited November 2014 in MTB workshop & tech
I took my Cannondale Trail 4 for a ride up Helvellyn the other week and was doing pretty well, until my rear mech decided to spin around and bend my cassette, chain and hanger. I managed to freewheel down with a buckled wheel, but without any problems.

As the bike isn't that old (approximately 6 weeks now), I took it back to the shop where I got it from with the intention of them fixing it. It turned out it was going to take 2 weeks for a new hanger to arrive, and I as a could get one online alot quicker I decided to order the part plus the other required ones (derailleur, casette and chain) and, being a mechanical fitter and always fixing my own bike, decided I would fix the bike myself. Wheel trued and new parts fitted and set-up, I ventured out onto some purpose built trails without issue, and also biked to work twice (a 30 mile round-trip) without any issue.

I today took my 8 year-old step-son out for a first ride on his new bike today, and I went on mine. Less than 10 minutes into our ride I hear something catching the spokes and immediately stop to find I have had a repeat of the previous issue, minus the gnarly descent.

In the first instance you can argue that the bike is substandard for the task I requested of it, but in the second instance this is most definitely not the case. Can someone help me figure out what has gone wrong and where I stand in terms of resolving this issue with my LBS? I don't feel like I've been asking anything excessive of the bike give the make and age, but feel I am left with another bill in a short space of time on a bike that should be capable of handling the use I gve it (I'm no downhiller!).

I replaced the mech with what was on (Shimano Alivio), but upgraded the chain and cassette to Shimano HG53 and HG50 respectively

Posts

  • cooldadcooldad Posts: 32,904
    Probably the low limit screw isn't adjusted properly - read Parktools for correct adjusting/indexing - link in sig.

    Riding over sticks and twigs can also snag the mech - only way to avoid that is avoid them.
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  • cooldadcooldad Posts: 32,904
    Reading your post again - if you've managed to bend the cassette, you must have pedalled like mad with things snarled up. Never managed that in close on half a century of riding.

    Also if you are using a Shimano chain with the silly joining pin, get a KMC or Sram with a master link. The pin is easy to fit incorrectly, which makes the chain split and can cause damage.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • cooldad wrote:
    Probably the low limit screw isn't adjusted properly - read Parktools for correct adjusting/indexing - link in sig.

    Riding over sticks and twigs can also snag the mech - only way to avoid that is avoid them.

    I had set up all adjustment screws correctly, and was nowhere near any twigs or debris as the path I was on is a decent piece of tarmac.
    cooldad wrote:
    Reading your post again - if you've managed to bend the cassette, you must have pedalled like mad with things snarled up. Never managed that in close on half a century of riding.

    Also if you are using a Shimano chain with the silly joining pin, get a KMC or Sram with a master link. The pin is easy to fit incorrectly, which makes the chain split and can cause damage.

    I was descending at the time, and fairly slowly with very little pedaling. It was only one sprocket on the cassette though, but still find that highly unusual. The chain had snapped previously to the first incident I mention and I had fitted one of the above mentioned quicklinks at that point. It was pretty rocky where it happened on Helvellyn, though I don't remember clattering the bike on anything at the time.
  • njee20njee20 Posts: 9,613
    Either you didn't adjust the stop screws or something bent the mech. They don't spontaneously shift into the spokes. Stop screw seems most likely given the second situation.
  • The RookieThe Rookie Posts: 27,747
    There is only one other thing I have seen cause this.....

    The cable outer was jumping out of a stop and sitting on the 'end' of it adding a LOT of tension to the cable, if the rider tried to downshift and used a reasonable force on the lever the cable force bent the mech into the spokes despite the stop being set correctly, on his bike in lowest gears the mech was only about 2-3mm clear anyway so it didn't need to bend much. Of course the lever was showing middle of cassette ish as it was several gears out due to the extra cable pull.
  • njee20 wrote:
    Either you didn't adjust the stop screws or something bent the mech. They don't spontaneously shift into the spokes. Stop screw seems most likely given the second situation.

    After 45 miles of riding and alot of gear changes I find it hard to believe that incorrectly set stop screws would show while not changing gear or pedalling hard. I've had bikes shift too far down and the chain has ended up between the cassette and spokes with the derailleur not catching the way it did.
    The Rookie wrote:
    There is only one other thing I have seen cause this.....

    The cable outer was jumping out of a stop and sitting on the 'end' of it adding a LOT of tension to the cable, if the rider tried to downshift and used a reasonable force on the lever the cable force bent the mech into the spokes despite the stop being set correctly, on his bike in lowest gears the mech was only about 2-3mm clear anyway so it didn't need to bend much. Of course the lever was showing middle of cassette ish as it was several gears out due to the extra cable pull.

    A possibility, as I'm not totally convinced my inner cable has been running smoothly through the outer. How much would too tightly cornered outers effect the shifting, and in what way?

    Is it possible the wheel being out of true has effected it? As I say it was out of true after the first incident, though I can't say I noticed anything before it (one of the slight disadvantages of disc brakes I suppose!). I did true the wheel up, but I'm no master wheel builder. Could there be this much flex in the wheel?
  • Chunkers1980Chunkers1980 Posts: 8,035
    I'm trying to work out what you're actually asking here. If you weren't happy and think it was all down to the bike then why did you change (and pay?) for the stuff yourself?

    http://hyperboleandahalf.blogspot.co.uk ... thing.html
  • cooldadcooldad Posts: 32,904
    Might have had a case against the LBS the first time it happened if it was supplied out of adjustment or something, but once you've replaced everything and trued the wheel yourself, I doubt it.

    SS is, however, the expert in righteous indignation and consumer protection.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • The RookieThe Rookie Posts: 27,747
    Devyhead wrote:
    The Rookie wrote:
    There is only one other thing I have seen cause this.....

    The cable outer was jumping out of a stop and sitting on the 'end' of it adding a LOT of tension to the cable, if the rider tried to downshift and used a reasonable force on the lever the cable force bent the mech into the spokes despite the stop being set correctly, on his bike in lowest gears the mech was only about 2-3mm clear anyway so it didn't need to bend much. Of course the lever was showing middle of cassette ish as it was several gears out due to the extra cable pull.

    A possibility, as I'm not totally convinced my inner cable has been running smoothly through the outer. How much would too tightly cornered outers effect the shifting, and in what way?

    Is it possible the wheel being out of true has effected it? As I say it was out of true after the first incident, though I can't say I noticed anything before it (one of the slight disadvantages of disc brakes I suppose!). I did true the wheel up, but I'm no master wheel builder. Could there be this much flex in the wheel?
    Smooth running is irrelevant unless it's causing the end of the outer to jump from it's stop. Wheel trueness would have a tiny effect as the radius where it is close to the spokes is very small, it would be a long way out at the rim to be significant.
  • RockmonkeySCRockmonkeySC Posts: 15,247
    Either something (mech?) is bent or the mech is incorrectly set up.
    Or you had your gears crossed up too far. Small gear on cassette to small up front or big to big.
  • The RookieThe Rookie Posts: 27,747
    Devyhead wrote:
    njee20 wrote:
    Either you didn't adjust the stop screws or something bent the mech. They don't spontaneously shift into the spokes. Stop screw seems most likely given the second situation.

    After 45 miles of riding and alot of gear changes I find it hard to believe that incorrectly set stop screws would show while not changing gear or pedalling hard.
    Just noted this and it is apparent from that that you don't know what a stop screw does, not a good sign!
  • Monty DogMonty Dog Posts: 20,614
    I suspect the bike wasn't set up correctly from new - probable causes were incorrectly stop-screws or less likely the gear hanger coming loose or a crash bending the hanger. Whatever the cause, over-shifting sent the rear mech into the spokes, wrapping it and the chain around the cassette. By not giving it straight back to the LBS to solve at the beginning you've allowed them to duck their liabilities, particularly as a repeat incident demonstrates you've repeated the same mistakes. See if you can come to arrangement with your LBS - you'll likely pay for the parts but I'd ask them to cover the labour as a gesture of goodwill.
    Make mine an Italian, with Campagnolo on the side..
  • I know what all the stop screws on my mech are for and how to adjust them, though my previous comment might suggest otherwise!

    I'm pretty sure I didn't cross the gears up too far, though i'm thinking something might be out of line.

    The first incident could have easily been my fault, hence my willing to repair it myself (plus it was going to take 2 weeks to get a new hanger from Cannondale vs 1 week on the internet and I didn't want to wait). I think my eagerness has been my undoing in this instance and has left me in an awkward place. I'm taking it to the LBS tomorrow to sort out, so then I'll know for sure if it was an original poor set-up furthered by a poor set-up from me, or there is something else amiss. Plus my censored is covered if the same happens again, though I think it may go in the skip at that point.
  • cyclecliniccycleclinic Posts: 6,865
    You may know what the limit screws do but 9/10 these problems are caused by the limit screw not set properly. Just because 45miles of riding had not caused a problem is no reason why it can't be the limit screw either as prior to the incident you had not over shifted enough.

    The other cause is bent mech hanger but on a new bike this is not common but not impossible.
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • The RookieThe Rookie Posts: 27,747
    Exactly, if the stop screw had never been called upon to do it's job in that small 45 miles, then that distance is no guarantee it was set correctly, especially (assuming you have a high normal setup) as it's not even on the stop screw with no cable attached. Therfore your suggestion that that distance proved it was set up right is either a mistake making it (no proof) or you don't understand what it's their for if you thought it did prove it!
  • My bet is that the chain is a touch short.
    It will seem fine until you cross gear it big to big and then hit a bump that drives the rear suspension deep into it's travel where it needs more chain.
    Too tight chain bends hanger and then the usual nasties that follow that happen with the deraileur now collecting the spokes......

    Drop the air out of the rear shock and see how it goes for chain length in big, big combo.
    If it is short, then it is certainly a warranty problem.
  • cooldadcooldad Posts: 32,904
    Bit of a thread resurrection - but it's a hardtail.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

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