Rear mech woes

the_jackalcp
the_jackalcp Posts: 276
edited August 2017 in Workshop
Typically I can sort my bike out however this time I'm beaten.

The setup - sram red 10sp shifters, 50/34 sram red chainset, red rear mech, force 22 front, 12-25 1070 cassette, KMC chain. The bike is a cervelo r3 with external cables

The Problem - when in 50/13 or 50/12 the gears do not run smoothly. The best way to describe it is that the chain is sticking to the upper jockey wheel. When it detaches it does so with a heavy clunk. It is roughly once per revolution of the jockey wheels but not always. I can correct the problem by using the barrel adjuster however this just shifts the problem to the middle of the cassette. With no cable attached to the rear mech the problem goes away. My assumption is there is an alignment problem, I just don't understand what is causing it.

What I've tried - New cables, cassette and chain are newish and same age/mileage. cassette torqued correctly and has correct spacers. Hanger has been aligned. limit screws adjusted, b screw also. Swapped the upper jockey wheel, problem persits

Any ideas, thoughts or solutions would be amazing

Thanks
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Comments

  • wiwaxy
    wiwaxy Posts: 16
    I'll wager that will be a bent rear mech hanger as I've encountered that recently myself.....
  • pinno
    pinno Posts: 51,196
    Try adjusting the gap between the jockey wheel using the much forgotten pulley screw*. The jockey wheel should be between 4mm and 7mm but check SRAM's spec, which with a quick google:

    *AKA B adjustment screw.

    "Step 9: Adjust the B-tension screw so that the pulley on the rear derailleur is as close to the largest cog on the cassette as possible without dragging."

    Obviously, if it's dragging, the gap isn't big enough.

    gears4.jpg

    Adjust the gap in 1st gear - it's easier to see.
    seanoconn - gruagach craic!
  • Been trying again today with a minor improvement. I've added a link to the chain and the noise/sticking has improved but still there.

    B limit screw has no impact and have gone through the hanger alignment yet again. Neither helped.

    Any other thoughts appreciated before the walk of shame to the LBS
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  • pinno
    pinno Posts: 51,196
    Okay. First the silly stuff, then the less silly stuff:

    Is the cassette worn?
    Is the chain worn?
    Is the jockey wheel worn?
    Is the jockey wheel cage bent?
    Have you got too many links/too few?
    I don't think it's a link issue as the biggest stretch of the rear mech and chain would be in the upper gears on the crossover point but you never know.

    http://www.machinehead-software.co.uk/b ... hcalc.html

    Does it run smoothly in other gears up the cassette?
    Is there a faint chance the chain is a 9 speed?

    Get through that lot and if it's still a no, then get back to me.

    ...but before I go, can you swivel the rear mech on the hanger easily? Does the spring feel just right, soft or sticky?
    How old is the mech or should I say; how many miles have you done on it?
    I'm just wondering if there is a little fraying of the cable in the outer section of the chain stay to rear mech and also in the BB cable guide that's not allowing the rear mech to sit properly or be adjusted with the B screw. B Screws are best adjusted in 1st gear - it's easier to see the gap there anyway.
    seanoconn - gruagach craic!
  • C_P_
    C_P_ Posts: 31
    Try a new length of cable housing to the rear mech and make it 30cm long.
  • @C_P_ - already done this but hasn't helped

    @Pinno - cassette and chain have no more than 300miles on. They were new at the same time.

    Chain length is fine and definitely 10sp, jockey wheels not obviously worn. Not sure how to check if the derailleur cage is bent? I would say it doesn't look entirely vertical.

    The other gears all run smoothly. There is a faint indication of the problem when in 50\13. If I use cable tension to correct the issue then the upper gears become very rough and noisy.

    The derailleur is newish, done a few thousand miles at a guess. It moves freely so no hint of a spring problem. The cables are brand new, this was what I expected to be the solution (or hanger alignment), so no signs of fraying. The problem existed prior to the new cables

    The b screw has been adjusted through out it's complete limits and at no point does it help. The problem becomes worse when the jockeys wheels are too close to the cassette but moving it further away is no help.
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  • pinno
    pinno Posts: 51,196
    If you physically move the rear mech so that the gap to the jockey wheels is bigger whilst pedalling (you might need some help to do this) does it help?
    seanoconn - gruagach craic!
  • StillGoing
    StillGoing Posts: 5,211
    I had a similar issue with SRAM Force and couldn't dial the problem out. In the end I stripped the rear derailleur, cassette and chain off, gave them a thorough degreasing in a solvent bath, put everything back and problem gone. Despite studious cleaning of the bike and components after every ride, the jockey wheels were gunged up to hell behind the plates and probably causing the wheels or chain links to stick.
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • pinno
    pinno Posts: 51,196
    philthy3 wrote:
    I had a similar issue with SRAM Force and couldn't dial the problem out. In the end I stripped the rear derailleur, cassette and chain off, gave them a thorough degreasing in a solvent bath, put everything back and problem gone. Despite studious cleaning of the bike and components after every ride, the jockey wheels were gunged up to hell behind the plates and probably causing the wheels or chain links to stick.

    ...and now we know why you call yourself 'philthy' but it's a good call.
    seanoconn - gruagach craic!
  • Jockey wheels have already been removed and cleaned however no improvement

    The bit I don't get in all this is that when the cable is detached it runs perfectly. As soon as I hook the cable up any gear above 13t runs very rough. Using the barrel adjuster fixes it but at the cost of 12&13.

    Shifter problem? Frame problem?

    @ Pinno - your suggestion of moving the jockey wheels by hand did nothing
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  • svetty
    svetty Posts: 1,904
    If the pivots are a bit gunged up it may be that the drag of the cable is enough extra load to prevent the springs in the pivots from moving the mech properly.

    Take the mech off, give the pivots a proper dismantle, clean and re-grease and this should sort it.
    FFS! Harden up and grow a pair :D