chain slip

matt21
matt21 Posts: 71
edited December 2013 in MTB workshop & tech
Hi all - Just gone back to the Mtb for the winter. I've stuck on a new chain and cassette (cut to correct length) and am getting really bad chain slip when under heavy pressure in the middle chainring only. Gears are smooth as ever and the new chain doesn't seem to have any stiff links. I've also adjusted the b screw but still no joy.
Having nearly face planted a couple of times I'd be grateful for any thoughts please.

Comments

  • mcnultycop
    mcnultycop Posts: 2,143
    Is the middle chain ring worn?
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  • matt21
    matt21 Posts: 71
    No - I wondered if it could be the front but it looks fine.
  • matt21
    matt21 Posts: 71
    Sorry - probably should explain. I used the bike for about 2 weeks and thought the shifting was starting to get a bit vague so replaced chain and cassette. Up til then there was no chain slip so I don't think it can be the front.
  • 97th choice
    97th choice Posts: 2,222
    If it only happens in the middle front ring then I think you've narrowed down the cause
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  • jimothy78
    jimothy78 Posts: 1,407
    Matt21 wrote:
    Sorry - probably should explain. I used the bike for about 2 weeks and thought the shifting was starting to get a bit vague......

    Do you mean 2 weeks from new (in which case I'd be very surprised if the drivetrain was worn in that time)? Shifting problem more likely to be due to the cable stretching if that's the case.
    so replaced chain and cassette. Up til then there was no chain slip so I don't think it can be the front.

    But if the bike wasn't new, and if the chain was worn, then it would also have worn the chainrings to match, so wouldn't slip until you replaced the chain, and now suddenly the chain doesn't match the chainring anymore, and might slip.

    Bit more detail about the bike's history needed to be sure what's going on.
  • matt21
    matt21 Posts: 71
    OK, that sounds quite likely then.
    The bike is a 2010 Rockhopper SL Pro and has probably done about 4500 miles so perhaps a new chainring might be in order to match the new chain. Thanks very much for that!
  • jimothy78
    jimothy78 Posts: 1,407
    Yep defo sounds right, now.

    Also be worth thinking about what other maintenance has been carried out, and what might need doing:

    If the wheel hubs have cup-and-cone bearings then they need to be stripped down, cleaned and reassembled with new ball bearings fairly regularly to prevent the cups and cones themselves getting damaged. Same with the headset too. (less of a problem if they use cartridge bearings, as then you just press out the whole thing and install new ones, but with loose-ball bearings, once the cups are damaged the hub/headset is junk).

    Gear cables need replacing every so often, too, and is one of the best was to keep your shifting nice and crisp. Worth servicing your forks too, if the bike's been sitting around unused for a while the seals may well have dried out or got manky.
  • mattv
    mattv Posts: 992
    If it was slipping before though its quite possibly the front mech adjustment. It takes one hell of a lot of wear for a chain to slip off a chainring. If it's been laid up for a while it could even be a sticky cable.
  • matt21
    matt21 Posts: 71
    Stout hubs have been regreased, new inners and outers, brakes re bled. Gear shifts are all as good as new - all's well till I stand up!
  • jimothy78
    jimothy78 Posts: 1,407
    Sounds good - while you're waiting for that new ring just gear down a bit and spin rather than punch the pedals, and it'll hopefully slip less.
  • matt21
    matt21 Posts: 71
    Yep, thanks for that - good advice.
  • Cqc
    Cqc Posts: 951
    Yeah, I'm getting the exact same thing, the chain is new for me too and I have wound in the barrel adjusters to account for cable stretch (cables new too) . gears seem to shift between the back cogs up and down for no good reason .any help for that? Rear Mech just got fixed by bike shop so shouldn't be a problem...
  • mattv
    mattv Posts: 992
    Shifting up and down at the back is a rear mech issue. Either the mech is bent, cable tension is wrong, or if it's hardest gear it won't settle in it could be limit screw.
  • jimothy78
    jimothy78 Posts: 1,407
    Cqc wrote:
    Yeah, I'm getting the exact same thing.... gears seem to shift between the back cogs up and down for no good reason .

    No, you're getting a completely different thing - original poster reports that shifting has not been affected, and is still working normally.

    If you're having shifting problems, then it's normally either the rear mech not being set up correctly or shifters/cables not running smoothly.
    As you've just replaced the chain, it could also be caused by not having the right chain (eg. an 8sp chain on a 9sp cassette).
    Also, whilst you say that the LBS has just "fixed" your rear mech, generally a bent or damaged mech is not really repairable - even if it looks alright, there could be loose or sticking pivots, or something out of line. What happened to it and what did they do to fix it? If it was damaged in a crash, the mech hanger could also have bent bent out of allignment - they should have checked that too, but might have neglected to do so.
  • Cqc
    Cqc Posts: 951
    They replaced the chain, the cables and the mech hanger and set up the limit screws and cable tension of the mech, so it's not the chain or the mech hanger's fault
  • cooldad
    cooldad Posts: 32,599
    Sounds as if they did a bit of a rubbish job if it doesn't shift properly.
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  • Cqc
    Cqc Posts: 951
    Yeah... :p could the cassette being worn cause this?
  • Chunkers1980
    Chunkers1980 Posts: 8,035
    Er yes. Hijacking makes it very difficult to help.

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