Viewing 18 posts - 1 through 18 (of 18 total)
  • help with gearshift problems
  • asterix
    Free Member

    Sometimes when I try to shift rear cogs on my road bike (105 groupset) the shift lever moves with no resistance and the rear mech doesn’t move. I have replaced all of the cables so that’s not the problem. So my question is do I need a new rear mech or a new shifter?

    chief31
    Free Member

    One of my old road shifters on a racer had like splines in then and they wear out so lever moves but not at the rear.

    asterix
    Free Member

    Hi, thanks for the reply. Thats what I was worried about. The local shop said it was a “lazy rear mech” but I not sure

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    asterix
    Free Member

    so is there any way to know for sure which (of the rear mech or the shifter) is worn out?

    lovewookie
    Full Member

    If the lever moves with no resistance (assuming the cable has enough tension) it sounds like the ratchet mechanism in the STI is sticking.

    Try fushing it out with degreaser to see it it’ll free it up. It may, if it does, you’ll need to flush it back through with something like spray summer chain lube to replace the grease.

    Ultimately though, it’ll not last too long so will need replaced.

    If you felt resstance but the mech isn’t moving, that’s what I;d call a lazy mech.

    asterix
    Free Member

    Thanks, that is really helpful. I’ll try but I expect to need a new shifter then

    b45her
    Free Member

    the 105 sti’s aren’t really serviceable, give it a clean out and see what happens your probably going to need a new unit though .

    jimc101
    Free Member

    Which 105’s? if the newer 5700’s check the condition of the cable, I had the same issue with a 6700, and it turned out that the cable was fraying at the exit of the shifter, replaced the cable, and shifting was back to normal.

    asterix
    Free Member

    yes it the older 105 shifters, so maybe not so surprising

    bigyinn
    Free Member

    Attack rear mech and shifter was a thin penetrating lube, operate by hand a number of times flush again, then repeat a couple more times. Remember to operate to the extremes of movement, ideally with cables removed. See if this frees things up. If so use a spray grease inside the shifter to relubricate it and use a thicker oil on the mech, give them a real soaking and let it soak in, again operating by hand.
    This may sort your shifting woes.

    spooky_b329
    Full Member

    When changing into a harder gear, if the cables are sticking or the mech spring is weak, it may not change up fully and this will leave slack inner cable which you should be able to see. When you change back to an easier gear the shifter will take up the slack so there will be no resistance and you are already in that gear, so it wont shift.

    lovewookie
    Full Member

    Spooky has a good point. You can check the cables easily if you don’t run full length as you can pop them out of the frame stops and check for free movement/corrosion/excess road dirt. Give them a clean, if they’re corroded at all, give them the once over with some medium wet n dry, clean lube and replace. if it works, buy and fit new cables.

    Remember to operate to the extremes of movement, ideally with cables removed.

    This is something I’d not recommend (and was something shimano tech guys advise against). If you operate STI’s with the cables out there is a chance, especially with old worn units that the ratchet return spring pops out and can become damaged.

    bigyinn
    Free Member

    That was more aimed at the mech than the shifters tbh.

    cookeaa
    Full Member

    I can manage to get a “dead shift” out of my tiagras if I flick both levers together in the right way, you sure you’re not catching the down and the up simultaniously?

    I did find an old MTB in the back of my dads shed not so long ago with a barely used STX group on it, the rear shifter was failing to fully up shift, so I dug about some more in my dads shed found some WD40 and flushed the shifter with that, 5 minutes of squirting and cycling the shifter through its range and I got it working perfectly, I think these things just gum up with age, probably that translucent snot that Shimano dollop in there…

    I bet you can free it up if you try.

    thomthumb
    Free Member

    i’ve got some 9sp 105s they don’t shift if you hit em too hard – i have wondered if it is a crash protection thing or if they are just worn out. 😕

    asterix
    Free Member

    I just checked. I have brand new cables on, all properly adjusted by the local shop mechanic – so I am assuming that’s not the cause. The problem comes when trying to shift to an easier gear (bigger cog) at the back. Sometimes (but not always) the lever just doesn’t seem to pull on anything. Have given it a good dose of lube.

    By the way it looks like 40-53 at the front with 13-26 at the back. Does that seem high gears to you?

    B_Leach
    Free Member

    I can manage to get a “dead shift” out of my tiagras if I flick both levers together in the right way, you sure you’re not catching the down and the up simultaniously?

    Yup, I’ve managed to do this a few times before on my 105 shifters. The up then pulls all the way round!

    asterix
    Free Member

    this puzzled me a bit because on the 105 lever I have, you definitely push both levers (brake and shifter) inwards to change to a bigger cog, but only flick the inner shifter lever inwards to change back to a smaller cog. Maybe they are an older design than yours?

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