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Help with derailleur(s) adjustment

Lefteris2310Lefteris2310 Posts: 10
edited May 2013 in The workshop
Hi all.

I have a bike with 21 speeds (7 rings in the rear derailleur and 3 rings in the front derailleur).

When I have the chain in the middle (2nd) ring of the front derailleur and in the smallest ring of the back derailleur everything is fine (at this point I am at gear 14).
When I get the chain to the next slowest gear (gear 13), this is at the 6th ring of the rear derailleur, still everything is fine. The same when I get down to the 5th, 4th and 3rd ring of the rear derailleur (gears 12, 11, 10 correspondingly). But then when I go to the 2nd ring of the rear derailleur (gear 9) and I push the pedal a bit hard (e.g. going up on a hill) the chain falls from the 2nd ring of the front derailleur to the smallest ring of the front derailleur (this is gear 2). The same happens if I go to gear 8 (in that case it goes even easier straight to gear 1)

In few words my bike does not stay in gears 8 and 9, but fall straight to 1 and 2 correspondingly.
Any idea what adjustment I need to make to which derailleur?

I sense I need to tune my front derailleur but I have no clue what to tune (low limit screw, high limit screw, the tension of the cable?) and how.

Any advice will be highly appreciated!
Thank you!

Posts

  • nicklousenicklouse Posts: 81,520 Lives Here
    I have no idea what you are saying.

    Small front an small rear are not combos you should use.

    Gets are not sequential and you have made it very hard to understand.

    What Front cog? And what rear cogs are you having issues? (Small is low in teeth so 12t rear 22t front and big is big in size).
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • I am sorry nicklouse for my bad description. I would blame my English, but I guess it is also my brain that gets slow lately.

    Regarding your comment "Small front an small rear are not combos you should use.",
    I have heard about it from others as well, but I have been using all possible combinations in my bike (including the one you mention) for years now and I had never a problem.

    Regarding your comment "Gears are not sequential and you have made it very hard to understand."
    you are right. But anyway, you can read my numbering as:
    gear 1 = chain in the smallest front ring and in the biggest rear ring
    gear 2 = chain in the smallest front ring and in the 2nd rear ring (which is right next to the biggest one)
    ...
    gear 7 = chain in the smallest front ring and in the 7th rear ring (the smallest one).

    gears from 8 to 14 = same description for 1-7 above, but replace "smallest front ring" with "middle front ring"
    gears from 15 to 21 = same description for 1-7 above, but replace "smallest front ring" with "biggest front ring"

    As for which cog is the one I am having issues with, I do not know.

    FYI, the problem started when I replaced my old rear wheel (which had a 7speed freewheel) with a new wheel that has a 9speed freehub (cassette) on which I plugged a 7speed freehub/cassette with the help of a 4.5mm spacer
    Okay, don't get upset, I know I only made my description even worse now!!!
    :shock:
  • owenlarsowenlars Posts: 719
    Rule of thumb is if your gear changes from a small rear cog to a large rear cog more easily than from large to small you need to loosen the gear cable by effectively lengthening the cable ( turn the barrel adjuster clockwise). If you have the opposite problem (easier large to small) than tighten the cable by effectively shortening the cable (turn the barrel adjuster anticlockwise). Sheldon Brown or Park Tools web sites give super details and there are myriad videos on You Tube showing how to do it.
  • bikaholicbikaholic Posts: 350
    OP, your problem as I understand it:


    chain_drop_issue_zps09549df9.jpg


    I don't think that this is a FD problem.

    The right-hand cage edge is responsible for derailling the chain onto a smaller front chainring. But, as you can see, as you shift from a smaller rear cog to a bigger one (from green to red), the chain is moving away from the right-hand cage edge.

    Assuming that the crankset and cassette are within a working chainline, that there isn't significant play in either the bottom bracket or the rear hub, then the problem is very likely to be chain related or chainring related and their inability to mesh together properly at that particular angle.

    Inspect the chain for twisted links (usually an inner pair of link plates); and inspect the chainring to see if it is bent (towards the right of center) or if there are any bent teeth pointing towards the right instead of straight up.
  • Dear owenlars, thank you for the tip! This sounds an easy way to have in mind for fast gear tuning. I am not sure if the cable tension is the issue with my problem. It may be or not. I will try to play with the tension anyway!

    Dear bikeaholic…WOW!!!! I pay respect to you!!!!!
    Not only you understood my problem, but also you described it with one simple picture, which is so accurate and much easier to understand than my hopeless long texts above.
    Now, about the chain (which by the way is brand new) and the crankset (which is old), they must have no problem, because they worked nice and sweet when I tested the gear shifting with my old rear wheel (which has a brand new freewheel on its hub).

    Well, I will try everything you all suggested and I will play with my gear set up until I find the solution (or until I mess it up lol). I will let you know.
    (no news will mean bad news)

    :)
  • Ok, the problem is solved!!!! :D

    I had to play a lot with both the front and rear derailleur, as well as the bearing adjuster of the rear derailleur. But at least what I understood is that the source of the problem was that the ring of the rear derailleur was not aligned to the ring of the cassette, e.g. when I had the 8th gear (i.e. orange line in the picture of bikaholic) the ring of the rear derailleur was much closer to the wheel than the biggest ring of the cassette.

    Thank you all!!!
    I am happyyyyyyyyy!!!!
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