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Chain doesn't go into Granny ring so easily

lonegringolonegringo Posts: 26
edited July 2014 in Workshop
Dear forum,
As the title suggests I have a problem whereby the change to the granny ring on my touring bike is not happening as smooth as I'd like. In fact I have to flip it to a higher gear on the rear in order to get the chain to catch on the small chainring and make the change. This is especially annoying at lights with an uphill start.
The chain is due for a replacement but i don't think that is the problem.
The front mech is at the maximum lower-limit (if that is the correct way to say it) - i.e. further adjustment of the limit screws will not allow additional swing to the left to push the chain further.
Looking at the bottom bracket installation, there is a good 2mm of thread on the left-hand (non-drive) side.

I am wondering if it is possible to install a spacer onto the drive side of the bottom bracket in order to give me an extra 1-2mm to play with in adjusting the front mech.

Specs:
Frame - Surly LHT 700c
Front Mech - Shimano Ultergra Triple
Chainrings & Crank - Shimano Deore Mega 9
Bottom Bracket - English 68mmx122mm, square tapered

The bottom bracket was installed new when I put the bike together, the chainrings are "new" last year, the crank is originally from my 2000/2001 Dawes Galaxy. Front mech is in perfect working order other than this problem.

Looking on the Surly website, the recommended size for the bottom bracket is actually 118mm - but I don't see how making the BB smaller would help in any way. A larger BB would also not be a good idea as the thread might not even reach the frame surely?

I took it to my LBS to explain the problem and they recommended getting the smaller BB but as per my reasoning above, I don't see how that would fix the problem.

I don't claim to be an expert so maybe I'm missing something here.

If anyone has had previous experience of this I would greatly appreciate some advice before any unnecessary expense.

Thanks
Lonegringo

Posts

  • team47bteam47b Posts: 6,424
    Maybe too obvious but does the mech move further if the cable is detached, could be the cable is preventing enough movement, frayed inner, gummed up etc if you release the cable and see if this creates more movement if not you have at least elimanated the cable as the culprit.
    my isetta is a 300cc bike
  • OuijaOuija Posts: 1,386
    Have exactly the same problem on one of my five bikes with a Deore derailleur and cranks. The limit screw and cable tension makes no difference as the derailleur is pressed up against the seat tube and can't move any further inwards towards the frame, even if it wanted to. It's not a setup problem as i know how to setup front mechs (my other four bikes work flawlessly).

    However, i would rethink the " I have to flip it to a higher gear on the rear in order to get the chain to catch on the small chainring and make the change" scenario. Mine is the same and it suggests that your cross chaining by trying to run the chain on the granny ring and the last two or three rings of the rear cassette at the same time. Something you shouldn't be doing any way if you want your chains to last any amount of time. If you want to be in a lighter gear your better off climbing most of the way up the cassette while still in the middle front ring AND THEN switching to your granny, rather than the other way round. With practice, you can train yourself out of these bad habits ;)
  • lonegringolonegringo Posts: 26
    Thanks for replies so far.

    In response to the second...it is not really a bad habit, more of a necessary evil - even in the middle of the cassette the granny ring wont catch. I know how to preserve a chain, believe me, with the price they are here in Brazil...3x what they cost in the UK.

    Could anyone offer a response to my direct query regarding the spacer?
  • deswellerdesweller Posts: 5,271
    The shell width of a BB with a longer axle is the same (68mm), so fitting one would push the chainline out a bit.

    I can't remember if square taper bottom brackets have the loose cup on the right or the left...if it's on the right then a spacer would also change the chainline, but would also move the left crank inboard. If you move it too far then you'll feel it.

    Has the bike always behaved this way since it was built? I would double-check the azimuth alignment of the front derailleur; it uses the trailing end to carry out the mid/low shift, so if the derailleur's toeing-in a bit then it won't drive the chain inwards enough.
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  • lonegringolonegringo Posts: 26
    Thanks, useful info there. To be fair the problem comes and goes, I recently did a thorough cleaning and it seems to have improved a little. I think a longer axel would be the way to go as I don't think I can afford to move the left axel inwards - I have a foot stand and the clearance is already minimal. I'll check the alignment of the front mech.
  • martinperrymartinperry Posts: 127
    Probably a silly question, but the BB is a triple isnt it?
    The axle is longer on the DS to accomodate the 3rd ring (or at least it is on my old Ult 6500 triple setup (octalink not square taper))
  • on-yer-bikeon-yer-bike Posts: 2,974
    Cable isn't tight enough.
    Pegoretti
    Colnago
    Cervelo
    Campagnolo
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