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Need front mech help

dubcatdubcat Posts: 737
edited November 2010 in MTB workshop & tech
Hi

I read up on how to adjust the front mech using the L and H screws at the park tools website. The L screw adjusted the front mech position over the small ring fine but i am having problems adjusting for the big ring with the H screw.

I put the rear gear in to the outside most cog and followed the instructions. The front mech needs to move out more as the outside of the chain is rubbing against the mech cage. Turning the H screw is having no effect at all. I tried the screw in it's tightest position and also tried loosening it to the point that the screw actually came out. The cage did not move at all. In order to get the cage in the right position i have to pull the cable which goes to the gear lever so that the little arm that the cable is connected to is lifted up to it's maximum height. Anyone know what I should do?

Dub
2010 Specialized Rockhopper
2012 Bianchi Infinito

Posts

  • nicklousenicklouse Posts: 50,675 Lives Here
    put it in the middle rear.

    the L and H screws do not adjust the mech. they are stops and stop the mech over shifting.

    the tension of the cable adjusts how it moves.

    sounds like more tension is needed.

    read the Park tools guide.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • dubcatdubcat Posts: 737
    I DID read the guide. The first step in the guide to adjusting the h screw is

    Shift to outermost sprocket in rear and outermost front chainring. Inspect derailleur for mark indicating H-screw.

    That's why I went to the smallest cog on the rear. Ok i see whet you mean about h stop setting the limit of the movement. I can now see that i need to tighten the cable. However, to get the mech in the right place i would have to tighten the cable so much that the arm it connects to is raised to it's maximum amount! Is that normal?
    2010 Specialized Rockhopper
    2012 Bianchi Infinito
  • supersonicsupersonic Posts: 82,708 Lives Here
    If that what it takes then yes.
  • dubcatdubcat Posts: 737
    Ok I will tighten the cable and use L and H screws to set the limits of movement and use the barrel adjuster to set the position on the middle ring as per instructions. Sound about right?
    2010 Specialized Rockhopper
    2012 Bianchi Infinito
  • nicklousenicklouse Posts: 50,675 Lives Here
    almost.

    set the L screw then the tensions so it shift up and down. the H screw is only really there to stop the mech moving too far. Setting the front mech with the rear in "5" makes it easy to get "close" and then tweek.

    So forget about the H screw for now as it does not really have much effect of the set up.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • dubcatdubcat Posts: 737
    Ok thanks. Will give it a go in the morning. Just to clarify, I use the l screw to set up the position for the small. I know the tension on the cable needs to be adjusted to get smooth shifting of the gears up and down right? Too tight and it won't shift down to small cog on front properly. Too loose and it won't shift up to big cog on front properly. Is that right?

    My confusion with the above is that i need to tighten the cable to get the front mech moved out more when i am on the big ring as it is rubbing. But, won't tightening the cable then also mean that i won't get a down shift to the small ring working properly as the cable will be too tight?

    Sorry to be so thick.

    Dub
    2010 Specialized Rockhopper
    2012 Bianchi Infinito
  • supersonicsupersonic Posts: 82,708 Lives Here
    Possibly - is the mech at the correct height and angle?
  • nicklousenicklouse Posts: 50,675 Lives Here
    and is the cable running free. not mucked up damaged.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • dubcatdubcat Posts: 737
    Thanks guys, between your advice and some YouTube videos i have got it sorted. I had to lower the mech and put some tension in the cable. It was all a bit more of a mission than it needed to be as i have lost all my pliers and had trouble grabbing the cable when tightening it :)

    Many thanks
    Dub
    2010 Specialized Rockhopper
    2012 Bianchi Infinito
  • dubcatdubcat Posts: 737
    Damn it... It was fine last night and on the ride. Got home, cleaned the bike, and as i was oiling the chain i noticed it's rubbing again in the middle cog front and back :(. This is taking the pee pee :(. If i tighten the cable with the barrel adjuster it gets worse. I cant loosen enough to make things better. Im not playing with this until I get some pliers. Am i going to have to adjust this after every ride? :(. If so I will invest in that park tools fourth hand tool.
    2010 Specialized Rockhopper
    2012 Bianchi Infinito
  • supersonicsupersonic Posts: 82,708 Lives Here
    If it was right to start, then something has loosened, or the cable tension has slackened.

    But also beware that flex under pedalling can cause rub too. Sometimes almost impossible to get rid of fully.
  • dubcatdubcat Posts: 737
    The rubbing is with me gently turning the peddles while the bike is up on the work stand. I am just going to leave it alone for now and take another look on Monday :([/quote]
    2010 Specialized Rockhopper
    2012 Bianchi Infinito
  • The RookieThe Rookie Posts: 27,802
    You don't need pliers at all, I never use them, scew the tensioner all the way in and then nip cable up, then use the adjuster to get it right, if itrs rubbing on the inside of the cage, then you need less cable tension, so getting more using pliers won't help!

    Is you cable sticky at al, if it is the mech won't return correctly as you go down the gears and will rub.

    Simon
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • dubcatdubcat Posts: 737
    Cable is definitely clean and free to move. What do you mean nipnthe cable up?
    2010 Specialized Rockhopper
    2012 Bianchi Infinito
  • diydiy Posts: 6,473
    Do you think your mech clamp might be loose?

    IME you first set the mech position, height and angle, then you set the stops, then you set the cable.

    But I would also clean the cables too and make sure the shifters are lubed.
  • Delta5Delta5 Posts: 264
    Hi Dub - sorry to see that mech is still giving you trouble. If I can chuck in my 2p worth of experience, I'd go back to setting it up as if newly fitting. Assuming clean smooth running cable and clean well-lubed mech, try this:
    1 - loosen off cable at the mech - maybe even detach it from the mech. It might help to remove the chain too until the basic setup is complete.
    2 - adjust the H and L screws to approx the middle of their range.
    3 - position the mech on the downtube - use your hands to push the mech in and out against its spring tension, checking the position allows
    a) the inner position to line up with the granny ring
    b) mech clears the teeth of the outer ring (by few mm - check your manual)
    This is the fiddly bit as you've obviously discovered! Once its correct tighten the mech clamp on the downtube. (This might be why yours reverted after being used as there's a fair bit of pull on that mounting when you shift front rings). Mark the mech position with a fine felt-tip, for future ref.
    4 - turn the barrel adjuster all the way in, then back ½ turn
    5 - from here you'll have to follow the specifics for you mech but basically attach and tension cable, pre-adjust H & L, test mech movement without chain, fit chain and test changing, adjust H & L if necc., and make final fine adjustment at barrel adjuster (usually just needs turning out a bit).

    Hope this helps, but if all else fails you could always upgrade to a twist-shift . . . :wink:
    My abundant supply of MTFU is reserved for use in dry, sunny conditions.
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