Viewing 35 posts - 1 through 35 (of 35 total)
  • Struggling with adjustment of gears
  • Premier Icon phutureproof
    Free Member

    Adjusting gears seems to be my achilles heal. I can bodge most other jobs on the bike, but I always seem to fail at this hurdle.

    I've just swapped my hibred bike frame from a Kona to an much bigger GT. I've moved all the bits over and everything works but the gears.

    The main problem is that I can't get the front mech to move over far enough to get onto the big ring. The rear mech doesn't seem to bad – a bit of ghost shifting on the smaller cogs.

    I've watched countless YouTube videos on adjusting the front mech, and they all seem so easy, but I just cannot seem to get it working properly. Can anyone give me any other tips.

    The mech is a Shimano Nexave. This is what I understand should work, which I have tried about 4 or 5 times now:-

    1) Move to largest ring on rear and smallest ring on front.
    2) Release cable bolt on front mech to slacken cable
    3) Make sure when you manually pull over the mech to the third (largest) ring, the gap between the mech and the outer points of the teeth of the large ring is about 3mm
    4) Make sure the alignment of the outer cage is lined up with the outer ring
    5) Spin the pedals and adjust the LOW screw until there is about 2mm clearance between the chain and the inside face of the front mech cage
    6) Pull cable tight and tighten hex-bolt
    7) Move chain to smallest cog on back and largest at front (I cannot get the mech to move chain onto biggest ring on front)
    8) Adjust HIGH screw until the outside face of the front mech cage clears the chain by about 2mm.
    9) JOB DONE!

    My problem is number 7) above. I cannot get the mech to move the chain over. The HIGH screw is screwed out as far as it will go! What am I missing here? Is my front mech the worng one for this bike frame???

    Premier Icon anjs
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    Has the chain line changed between frames?

    Premier Icon phutureproof
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    Not sure. By that, I guess you mean the angle between the large ring and large cog/small ring and small cog?

    Premier Icon stumpy01
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    Last time someone had this problem it was because the BB width of the two frames was different….with the new one being wider than the old one. I'd check that first.

    If it's not that, then are you routing the cable correctly into the mech?

    Premier Icon phutureproof
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    So if my BB is wider on this new frame, what does that mean? (I can't check this until I get home)

    Do I need a front mech with a bigger throw or something?

    Premier Icon stumpy01
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    What type of BB do you have?
    If it's a 'modern' BB with cups that screw in either side (with spacers) like a Hollowtech II, then you probably just need to remove the spacers from the drive side.

    Depends on the bottom bracket type though I think, so you should probably refer to a manual for specifics.

    Premier Icon phutureproof
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    Its a square taper BB, that much I know. I bought the frame second hand and it included the BB, so I've never had to inspect it closely. I've tried hunting around t'internet to see what size the BB is, but with no luck. Do I have to take it out of the bike to see what size it is?

    Thanks for all your help…

    (Its a GT Transeo 3.0 frame, and I've moved over from a Kona Dew Deluxe)

    Premier Icon phutureproof
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    Premier Icon phutureproof
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    Trying to post an image but it doesn't seem to be working…

    Premier Icon stumpy01
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    Ah – sq taper BBs are specified on shell width (width of the bottom bracket part of the frame) and length of the axle.

    If you follow this link:

    http://www.chainreactioncycles.com/Models.aspx?PartnerID=79&ModelID=17473

    you'll see there's 68, 70 & 73mm shell widths available and in each of those sizes, a number of axle lengths. If the shell widths are the same (I assume they are as the BB went in OK, but you should still measure this), then it sounds like the axle length is too long for the new frame, which is making the chainset sit too far out, in relation to the front mech.
    You'd need to speak to someone more knowledgable than myself to find out what axle length you need though, or you might be able to work it out.

    Premier Icon S_J
    Full Member

    Couple of things to check here.

    1. That all the cables are new. Old cables will often never index correctly regardless how much you try and tweak the tension.
    2. As it's square taper there's no issue with spacing on the BB.

    Other than that, you've missed one key stage in the front mech adjustment on your list above, which ensures that the cable tension is correct. Shift into the middle ring and the largest cog on the cassette. The chain should clear the front mech inner plate by 0.5mm – any more of less and the tension is wrong and you wont be able to shift properly. You almost want the chain just brushing the mech. If you find there's not enough adjustment in the barrell adjuster there is too much tension in your cable. Disconnect the cable completely from the mech and wind out the barrell adjuster on the shifter as far as it will go then back in two turns. Re connect the cable ensuring it is taught but not over tight. Repeat the above steps until your clearances are correct and you can shift in all rings. Front mech set up is always trial and error but you should be ok if you stick with it!

    Good luck!

    Premier Icon antigee
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    small thing missing from list (i think) before 6 hold cable tight and click the shifter to right position
    – possibly obvious but there you go

    Premier Icon phutureproof
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    A question about the barrel adjuster. The bit you turn with your thumb and forefinger almost feels like it is on a spring. You can pull it away from the gear casing and see what looks to be a grub screw inside it. I assume when you say unwind it as far as you can, you essentially mean until the 'grub screw' comes off, then wind back in a couple of turns?

    Also, to clarify, the fact that I have a square taper BB means there is no issue of the front mech being the wrong size? In other words, as this front mech fits on the frame, and the cable comes around and under the BB, it should work?

    Premier Icon phutureproof
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    Disconnect the cable completely from the mech and wind out the barrell adjuster on the shifter as far as it will go then back in two turns. Re connect the cable ensuring it is taught but not over tight. Repeat the above steps until your clearances are correct and you can shift in all rings. Front mech set up is always trial and error but you should be ok if you stick with it!

    Should I do this whilst on middle chainring (and on '2' on shifter)?

    Premier Icon S_J
    Full Member

    You dont want the adjuster to come out completely, but if it does just wind it back in a couple of turns.

    Yes you need to use the front shifter adjustment on the left hand shifter only the rear shifter is irrelevant for this adjustment You also need to be in the middle chainring. If the inside plate of the front mech is too far to the left of the chain wind on some tension until you get the correct clearenace and visa versa. You should see the cage move across as you wind the adjuster. Look down on the mech over the chainring as you adjust it.

    The only other thing that could be stopping this working is the height of the front mech on the seat tube. if it's too low the cage will foul on the middle chainring as it tries to move across to the bid ring. Have a visual check that this is not happening and move it up if it is.

    Otherwise, I can't think of any other reason this shouldn't work.

    Premier Icon phutureproof
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    Could it be the way I have clamped the cable into the mech? The cable comes around the underside of the BB and the allen bolt it connects to has a weird clamp kind of a thing. It could be that I have clamped the cable underneath this rather than above it…

    It wouldn't make very much difference anyway I don't think.

    Premier Icon S_J
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    If the cable wasn't routed properly it probably wouldn't work at all so I think that's unlikely.

    Premier Icon phutureproof
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    I was wondering if I had tightened the driveside cranks on enough, but I have put a good deal of pressure on the large allen key on that side. I can't imagine it would move much more.

    Will have a fiddle tonight.

    Premier Icon tron
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    Often it's difficult to get the cable tensioned up enough. Try doing the low limit up a bit before you tension the cable.

    Premier Icon phutureproof
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    I have noted that the amount of tension is huge. Its difficult enough to manually pull the cage over by hand!

    Premier Icon epicyclo
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    Never heard a better justification for going single speed or hubgear.

    Premier Icon phutureproof
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    I tried the SS route a few years ago. Awful. Never git the gearing ratio high enough for my pedalling speed, and when I hitched my daughter's trailer on, the gearing was too high to pull her up any hill.

    Premier Icon phutureproof
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    Now if I could have a single big ring up front and my 8 gears on the back, that would be ideal. Not sure how I'd do that though.

    Premier Icon Ax3M4n
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    One trick I saw was to twist the front mech cage on the seat tube so it is at a slight angle to the plane of the chainrings. Most instructions will tell you that the cage needs to be parallel with the chainrings. I found that the High and Low grub screws on max settings (SRAMX5) did not allow enough sideways travel across all 3 chainrings – if it was adjusted nicely over the big ring it would not go back in enough to reach the granny ring – and vice versa.

    The solution? Loosen off the seatpost clamp, twist the cage slightly so the rear end of the cage is further away from the centre of the bike than the front. If you were looking down the seat tube – this would be an anti-clockwise twist. It might take a few very small twists to get it right.

    Premier Icon epicyclo
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    phutureproof – Member
    Now if I could have a single big ring up front and my 8 gears on the back, that would be ideal. Not sure how I'd do that though.

    It's called an Alfine

    Premier Icon soma_rich
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    1. That all the cables are new. Old cables will often never index correctly regardless how much you try and tweak the tension.
    2. As it's square taper there's no issue with spacing on the BB.

    Really???

    If you oil the outers first the cables will be fine unless they are really old or kinked.

    What if the BB axle is too short? Then you need a new BB. so there will be a spacing issue.

    Premier Icon kaiser
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    couldn't be bothered to read all the posts but if you have clamped the cable incorrectly on the mech (which with some mechs is easy to do) you never get the thing set up properly as this will alter how much the mech moves in relation to the cable pull.

    Premier Icon phutureproof
    Free Member

    couldn't be bothered to read all the posts but if you have clamped the cable incorrectly on the mech (which with some mechs is easy to do) you never get the thing set up properly as this will alter how much the mech moves in relation to the cable pull.

    I had wondered about this, but I cannot find a picture of what it should be like.

    Premier Icon phutureproof
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    What if the BB axle is too short? Then you need a new BB. so there will be a spacing issue.

    My replacement frame came with the square taper BB in place, so I haven't had to remove it. The mech that I have moved from my Kona bike onto this fits the frame, and the cable rooting is the same on the replacement frame as on the Kona frame (ie under the BB), so does that mean the mech is OK?

    Or are there specific mechs for specific square taper BBs?

    Premier Icon mefty
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    The BB on the new frame may have a longer axle than the old one so the ring may be further away from the seat post and thus too far for the mech.

    Premier Icon phutureproof
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    The BB on the new frame may have a longer axle than the old one so the right may be further away from the seat post and thus too far for the mech.

    Aha. Didn't realise front mechs were BB-specific.

    Premier Icon phutureproof
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    Looking on CRC but can't find front mechs that are specific to BB axle length. Any ideas?

    Premier Icon mefty
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    They are not – but different chainsets use BBs with different length axle though the difference is not normally significant however it can be up to 15 to 20 mm which might be too much of a stretch. Worth measuring the axle lengths of the old BB and new one to see if this could be the reason.

    Premier Icon phutureproof
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    Right. My wife (who is at home next to my kona frame) tells me the distance between the ends of the tapers is 12cm. Looking at the CRC website, this could either be the 118mm or 122mm BB size. I guess if my GT frame has the 127mm BB size axle, that 5-9mm extra width would be enough to prevent my front mech from being able to shift over far enough…correct?

    Premier Icon mefty
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    Could be – worth installing your old BB to see if it works then.

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