Caliper brake won't stay centred

chedabob
chedabob Posts: 1,133
edited April 2012 in Workshop
Every couple of weeks I have to recentre my front brake. It's twisting around the bolt that attaches to the fork. I've done it up pretty tight but don't want to do it too much as it's a carbon fork.

Usual procedure for centreing it: Screw adjustment screw on top in all the way and then back out 5 turns, then undo bolt on the back of fork. I then pull the lever tight and do up the bolt on the back. It's usually well off centre at this point (it seems that tightening the bolt, even with the lever to the bar, causes it to twist), so I twist the caliper by hand, and then use the top screw to fine tune the centreing.

At this point it's dead centre and there's no movement of the wheel at all. It stays like this for a few weeks and then one side will start to rub. At this point, the top screw does bugger all (it seems to only move one side out, which isn't the one rubbing), so I have to repeat the process again.

Am I doing something wrong? Am I misunderstanding what that top screw does? I did tighten the bolt on the non-driveside of the caliper, which I think might have made things worse.

Edit: The calipers are unbranded. There's no identifier on them, and they didn't come with a manual.

Comments

  • balthazar
    balthazar Posts: 1,565
    I usually ignore the grub screw and use a cone spanner on the central bolt (if it has spanner flats) to turn the entire caliper appropriately.
  • I'm afraid to say that your usual process is pretty much completely wrong.

    To quickly explain, tightening the nut at the back is for fixing the caliper to the bike and, assuming you're referring to dual pivots, the screw on top is only for making fine centering adjustments. It is the step as suggested by balthazar that you're missing and is the primary method for centering the caliper.

    Holding the caliper against the rim or pulling the lever whilst tightening the nut counter-clockwise doesn't help centre the brake because the main bolt will also rotate counter-clockwise despite your best efforts to hold the brake in place.

    To remedy the situation, undo the rear nut and recentre the small screw on top to save for making fine centering adjustments once the brake is centred. Now tighten the rear nut as usual BUT THEN centre the caliper by using cone spanner on the flats on either side of the spring. Finally, use the small screw on top to make any fine adjustments as and when necessary.

    HTH