Rear mech problem - won't shift gears

joah
joah Posts: 29
in MTB workshop & tech
Hi all,

The rear mech on my son's Hoy 20" bike seems to have gone. It started by not being able to move the chain up to the first gear. Now it won't move it up or down at all. I can push the mech up to slacken the chain, but I don't think it's moving in or out.

Does anyone know what might be wrong and if it's a simple fix? If it's more complicated, do you know roughly how much it should cost to get it fixed by a LBS? My LBS is currently shut and the nearest one that's open, let's just say I'd like to have an idea of what it should cost.

Many thanks in advance!

Josh

Comments

  • steelo
    steelo Posts: 542
    There's lots of things that can contribute to a poorly shifting rear mech. If everything looks to be moving as you'd expect then it could be that the frame or mech hanger are bent/damaged which means the mech is out of alignment and won't shift correctly. Is everything clean and lubricated?

    Have a look at Park Tools website for their guide on re-aligning a rear mech, see how far you get if you dare otherwise it's a LBS job.

    Bottom line - if you can't fix it yourself then you'll have to pay whatever the LBS want to charge you. Hopefully a decent LBS will only charge you for the labour as long as all the parts are good to go.
    Specialized Rockhopper '07
    Trek Fuel EX8 '09
  • fenix
    fenix Posts: 5,437
    I think the gear cable might have slipped. Look at that first.
  • steve_sordy
    steve_sordy Posts: 2,443
    My LBS charges £10 to index the gears. That is assuming that there is nothing actually wrong with cables or parts. If the cables are shot, then that's another £10. If something is broken, then they should identify that pretty quickly and ring you on your mobile number that you left them to see what you want to do. They should tell you something like, "the rear mech is completely broken and a new one is required, that will be £X plus £Y fitting" (that will include indexing).

    Bike shops are very busy right now fixing all the bikes that have been left at the back of the garage for the last 12 months.
  • fortyone
    fortyone Posts: 166
    If you can push the rear mech in by hand and move through the gears that way, then the mech is unlikely to be the problem. fenix could be right regarding gear cable - is it clamped to the rear mech properly with sufficient tension in the cable?
  • pilot_pete
    pilot_pete Posts: 2,120
    If you undo the cable clamp and free off the cable inner, you can test the mech moves freely by hand. If it does, all the way in and out to top and bottom gears, it is more likely the cable or the shifter.

    With the cable inner free, hold it with some pliers and apply slight pressure (pull on it). Shift the shifter to see if the cable moves in and out as expected. Go through all the gears. If it moves freely, the chances are either the hanger is bent and/or the indexing and end stop adjustments need setting up properly.

    If the inner doesn’t move correctly or freely, I would remove the inner and inspect it looking for frayed strands etc. You will have to replace it with a new one if you remove it but they are very cheap. Can you inspect the shifter to ensure it operates correctly?

    I’d try a new cable inner first and make sure the hanger isn’t bent. If the new inner still doesn’t move freely I would fit a new outer and ferrules. Assuming the hanger is straight (you can’t tell exactly by eye alone, but you will see a badly bent one), then fit the new inner and outer if appropriate. Follow the derailleur’s set up instructions to check end stops and then clamp the cable and index the gears.

    If they still don’t work it is likely a problem with the shifter which may, or may not be repairable.

    PP

Categories