H and L screws and cable barrel don't affect the position of derailleur

Victor1687Victor1687 Posts: 5
edited June 2018 in Your mountain bikes
What's up guys, how are you doing. I have a problem with a rear derailleur and and H and L screws:
It doesn't seem that turning them affects the derailleur's position anyhow. Notice that the higher pulley(which is closer to the cassette) is stationed relatively straight, though not indexed to the corresponding sprocket, while the lower pulley is skewered quite decisively from the straight line. Begging your pardon for the improvised terms, but I hope you've understood what I mean. Now, with the derailleur in this state, the gears are jumping while riding like a madmen, and the chain is going off from the sprockets at all sometimes.
Could you please suggest how to fix this issue, desirably without buying any new spare parts. Though if it's necessary tell please what exactly it's required to be bought.
I'll attach the picture as far as I know how to do that.

Posts

  • Chunkers1980Chunkers1980 Posts: 8,035
    H+L screw are limit. They stop the mech moving too far either way, to stop chain over shift. The barrel adjuster just ensures the mech moves one cog width with the first click of the shifter, so it is sitting H limit.
  • keef66keef66 Posts: 13,286
    The H & L screws just set the limits for the movement of the derailleur so it can't overshift into the spokes or jam the chain between cassette and the frame The barrel adjuster is used for fine tuning the indexing.

    But from your description it sounds like the derailleur cage may be twisted or the derailleur hanger bent. Hard to diagnose over the interweb but a picture would help
  • fenixfenix Posts: 4,676
    Try bending the lower part of the cage so it is in line with the top part.

    If you can get that fixed then you need to align the yop jockey wheel with the correct sprocket.

    You do that by altering the tension in the cable.

    As has been noted H/L only matter with the high and low end of the gears.
  • fenix wrote:
    Try bending the lower part of the cage so it is in line with the top part.

    If you can get that fixed then you need to align the yop jockey wheel with the correct sprocket.

    You do that by altering the tension in the cable.

    As has been noted H/L only matter with the high and low end of the gears.
    Thank you very much for your instruction, man. I just would like to confirm one point of it, you say "try bending the lower part of the cage". Do you mean just to bend it by applying the force to the side of it manually without turning any screws, like bending the tin rod?
  • fenixfenix Posts: 4,676
    Yes dont' turn any screws - it should align perfectly underneath the top jockey wheel - no matter what gear you are in.

    Only once it's straight-ish is it worth looking at dialling in the tension of your rear mech.
  • larkimlarkim Posts: 2,216
    If you can get the bike into a convenient position to look at the derailleur directly, use the shifter to select the highest gear (i.e. the smallest cog at the back) and then get your screwdriver out on the H screw. If you look closely, you'll see exactly how it works - with the screw loosened as far as possible, the "other" end of the screw won't be touching any part of the derailleur. But as you screw it in, at some point it will touch the derailleur and from that point onwards every small turn will move the derailleur arm inwards (i.e. towards the spokes). So if you've fiddled a lot with the H screw you might find that it is currently not in contact with the mech and therefore really isn't doing anything.

    Once I'd taken that close look to see how simple it was it really helped me to get my head around what the two different screws do - the L does the same sort of thing, but in the opposite direction and only at the point at which the mech is full shifted over to the lowest (easiest, biggest back cog) gear. It's a really simple thing, but there's a common misconception that they affect shifting across the range, which they don't.

    In terms of the bent pulley cage, straightening it might be solid advice, but I'm no expert.

    In terms of setting the cable and screws correctly, assuming the rest of the mech is working fine and the hanger from the frame is not bent, the park-tools website guide is the best way to step through setting it all up.
    2015 Canyon Nerve AL 6.0 (son #1's)
    2011 Specialized Hardrock Sport Disc (son #3s)
    2013 Decathlon Triban 3 (red) (mine)
    2019 Hoy Bonaly 26" Disc (son #2s)
    2018 Voodoo Bizango (mine)
    2018 Voodoo Maji (wife's)
  • JBAJBA Posts: 2,347
    Stop randomly fiddling and watch THIS VIDEO.
    It explains how to set up your gears and shifting and what the various adjustments do.
    “Life has been unfaithful
    And it all promised so so much”

    Giant Trance 2 27.5 2016 ¦ Bird Zero Mk1 ¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
  • milemuncher1milemuncher1 Posts: 1,472
    If you put the system in it’s lowest tension ( wind the barrel adjusters anti clockwise as far as you can, put the gears into the smallest ring at the front and smallest sprocket at the back) then undo the pinch bolt on the cable in the mech, give the cable a small tug, and hold it under tension whilst you re tighten the pinch bolt, you may then find that the barrel adjuster starts working again.
  • steve_sordysteve_sordy Posts: 1,382
    JBA wrote:
    Stop randomly fiddling and watch THIS VIDEO.
    It explains how to set up your gears and shifting and what the various adjustments do.

    VERY good advice! 8)
  • Thank you very much guys, I'll try your advises presumably on this week and write a reference. The video the reference to which you've posted did't help too much though, cause I've already seen it. The thing is all those turning don't affect the derailleur cage in this particular case. I've found another video though which was of more avail to me. Here it is https://www.youtube.com/watch?v=TnwreRrorIA . I guess it's the solution Fenix was suggesting. But before fallowing it, I'll probably try the advise Milemucher1 has given.
  • JGTRJGTR Posts: 1,404
    As JBA said, you need to start from scratch as you’ve been messing with the H & L screws. H & L is set without cable tension and just sets the range of movement if the derailleur. You then connect cable and fine tune with barrel adjuster. Check out Parktool website.

    But if your derailleur hanger is bent then it’s a non/ starter as it won’t work. I wouldn’t “bend” anything either as you’re likely to do more damage.
  • cougiecougie Posts: 22,512
    Well as it is it's not going to work with a bent mech.

    It might break if you bend it but that's never happened to me.

    If you don't bend it you will need to buy a new one.

    Starting from scratch is a good idea.
  • larkimlarkim Posts: 2,216
    Just out of interest, if the bottom pulley wheel is out of line, but the top pulley wheel is bang on in the right place, does that actually have any impact on shifting / indexing? I'm trying to rationalise that in my head, but I keep coming back to the thought that if the top wheel presents the chain correctly to the cassette, it shouldn't be an issue if the bend is relatively minor.
    2015 Canyon Nerve AL 6.0 (son #1's)
    2011 Specialized Hardrock Sport Disc (son #3s)
    2013 Decathlon Triban 3 (red) (mine)
    2019 Hoy Bonaly 26" Disc (son #2s)
    2018 Voodoo Bizango (mine)
    2018 Voodoo Maji (wife's)
  • larkim wrote:
    Just out of interest, if the bottom pulley wheel is out of line, but the top pulley wheel is bang on in the right place, does that actually have any impact on shifting / indexing? I'm trying to rationalise that in my head, but I keep coming back to the thought that if the top wheel presents the chain correctly to the cassette, it shouldn't be an issue if the bend is relatively minor.
    I checked it again after you've asked, and I'm afraid you're right man. The higher pulley seems to be in line with corresponding sprocket cause it's closer to it than lower pulley. In fact the whole cage seems to be tilted. I'm afraid the problem is with the derailleur hanger indeed. It seems the only way to fix this is to try and bend it back, though Mr JGTR discourages me from doing so, but it looks looks like there is no other choice cause, as far as I understand, the hanger is welded to the frame which means that it's impossible just to buy a new one without buying a whole new frame. Which is in this case is quite cumbersome cause it's a full suspension bicycle and the frame, apart from being the most expensive part in any case, is gonna cost very much in this particular circumstance.
    Anyway, thanks for your advices, chaps. BTW, by starting from scratch do you mean buying a new frame? Cause if I fail to fix the hanger correctly, it seems to be the only option. Though it would be much better if I yet manage to fix it.
  • keef66keef66 Posts: 13,286
    If the hanger is part of the frame rather than screwed / bolted on, it's likely made of steel so it should survive a bit of bending.

    Take the chain and rear mech off and remove the rear wheel to check. Some replaceable hangers are very neatly integrated into the dropout so they can appear to be part of the frame, especially on a mucky bike.

    Easiest and safest way to properly align a hanger is using the correct tool. It's also possible to use a spare wheel with a threaded axle which you screw into the hanger. Finally there's a big adjustable wrench and trial and error - keep reinstalling the rear mech till it looks like the pulleys are vertically aligned below the sprockets.
  • larkimlarkim Posts: 2,216
    WHat bike is it? A full suss without a replaceable hanger sounds unusual, but if it's a very low end or old model that might explain it.

    Photos always good too to show the issue!
    2015 Canyon Nerve AL 6.0 (son #1's)
    2011 Specialized Hardrock Sport Disc (son #3s)
    2013 Decathlon Triban 3 (red) (mine)
    2019 Hoy Bonaly 26" Disc (son #2s)
    2018 Voodoo Bizango (mine)
    2018 Voodoo Maji (wife's)
  • keef66keef66 Posts: 13,286
    My son's budget Saracen FS had a steel rear triangle. The thing weighed a ton, but it did mean I could straighten the hanger with a large adjustable spanner when he snapped the rear axle which wrote off the mech when it went into the spokes.
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