Help: Brompton gear cable tension adjustment

Discussion in 'Folding Bikes' started by Carranty, 28 Apr 2018.

  1. Carranty

    Carranty Regular


    My 6 speed Brompton is having a lot of trouble downshifting in the left-hand gear. The sturmey archer hub is working fine, but the chain isn't going from the small sprocket to the large sprocket when I shift using the left hand gear lever. It has no problem moving from the large sprocket to the small sprocket (upshifting).

    I've followed Brompton's technical guide for 2 speed gear adjustment. I've checked the max/min position of the chain pusher (its fine), then the guide moves on to adjusting the gear cable tension at the shifter end, but its using the old style shifters, and I have the new style. I've tried this afternoon to adjust the tension at the shifter but I can't figure out how to do it!

    Can anyone help me out?
  2. Justinitus

    Justinitus Someone mention cake??

    If you have the new style integrated shifters, there is a tension adjustment on the left derailleur shifter. Where the cable enters the shifter, that part pulls outwards (about 5mm) and you can then turn it - counter clockwise to increase tension (I think!).

    Firstly, I’d check that the derailleur and actuator ar all moving freely both ways and isn’t gunged up - my actuator was... badly! The following links shows the details:

    Worth mentioning, the bolt marked M3 on the diagram on page 3 should not be tight - nip it up then loosen 1 turn. It’s supposed to have some play.
    Last edited: 29 Apr 2018
  3. Schwinnsta

    Schwinnsta Active Member

    The chain pusher has indents where high/low screws hit again the sides of the indents. Dirt gets in the indents and prevents the screws from traveling all the way preventing the shift. It is design problem but if you keep it clean, it work OK.
  4. Kell

    Kell Über Member

    Quite often a bit of degreaser and an old toothbrush will be enough to get it shifting.
  5. alanowens

    alanowens New Member

    I had the same problem and traced it to a small black plastic cable holder that is near the front of the chain stay. It is supposed to clip on to a small bar above the chain stay to hold in place, but that had been pushed off (I suspect by the rear mud guard when folding).

    Without it properly in place you could not get enough tension on the cable to shift up to the smaller cog. It just pushes back on - and that solved it for me. As above you can use the barrel adjuster at the shifter end to fine tune.

    Excuse the generally grubbiness and need to lube the chain :/, and admire that weld instead IMG_1480.jpg
    12boy likes this.
  6. u_i

    u_i Active Member

    I strapped that piece of plastic, in which the cable housing ends, with a zip tie to the chain stay, to prevent it from moving off.
  7. chriscross1966

    chriscross1966 Senior Member

    Frayed inner cable? Worn cable outer ferrule ?... also the shifter mech has a lot of small bits in it that need to slide etc so a thorough strip and clean ... given the price of the bits I don't think Brompton expect it to not be replaced occasionally
  8. Kell

    Kell Über Member

    I'm hoping they might have sorted it by now as it's been 11 months since the initial post...
    ukoldschool and chriscross1966 like this.
  9. 12boy

    12boy Über Member

    Casper WY USA
    Thanks, alanowens. I too was having shifter problems. My next step would have been to use a rear derailleur shifter as it has a larger throw than the SA 3 sped shifter I have been using, but the ziptie strategy seems to work fairly well. Simple and easyso thanks again.
  10. kais01

    kais01 Regular

    hope carranty solved the problem. the two-speed derailer of brompton is normally low-maintenance, but fiddly to set up properly.

    one reason for that is there is spring interaction also when you go to the larger sprocket. the lever is not directly connected to the derailer, but via a spring. which has to be balanced against the spring working in the other direction and responsible for moving the chain passively to the smaller sprocket.

    so these spring forces have to be balanced against each other

    adequate lubrication is a good start.
    12boy and chriscross1966 like this.
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