Brake Alignment

Discussion in 'Cycling Equipment' started by Guest, Nov 20, 2001.

  1. Guest

    Guest Guest

    I always check the alignment of my brakes right before and after a ride. Around 30% of the time, I find them out of alignment, and sometimes even rubbing the rim after a ride. What cause the caliper to move like this? It's already kinda bolted on tight.
     
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  2. Vo2

    Vo2 Member

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    Had that with one of my old bikes too. I was never able to sort it out, even after a complete overhaul of the calipers.
     
  3. Guest

    Guest Guest

    It's very frustrating! One day, I was trying to keep up my speed, but it seemed like I got weaker or something. I get home, check the bike, and voila, the brake pad is rubbing!

    Good to know it wasn't me though :)
     
  4. Guest

    Guest Guest

    Hi. I don't have any experience with the higher-quality brakes used on modern road-racing bikes, but here's how what I do, to centralise caliper brakes. It's an old trick I learnt in a bike shop, years ago. A little crude perhaps, but very effective.

    You will need three or four items:
     A small to medium hammer,
     A drift, or pin punch, or a length of 1/4", 6 m/m rod, or similar
     Care and Patience.

    First ensure that the brake shoes are set correctly against the rims, and that the nut is tight at the mounting. Also adjust
    the front to eliminate slack in the arms ( so they don't rock
    forward when contacting the rim ). I generally use a 10 m/m socket on the domed nut, and an 11 m/m Park,thin, flat spanner on the adjusting nut.

    Now place the drift on the brake spring - on the side of the brake which has the bigger gap - and give it a tap with the hammer. No change? Another tap, a little harder.  Oops, moved too far? Tap the spring on the other side to bring it back. Operate the brake lever after each tap, to see where the arms settle. Works fine for me everytime, and stays put for a long time.

    Sheldon Brown's website has a wealth of information on brakes, among other things.

    I think that the two arms of the one-piece spring have unequal tensions, and thus the brake tends to want to centralise itself accordingly, which is not neccessarily the centre of the forks.  This inequality may be caused by minor differences in the heat-treatment of the spring - the quenching, tempering, embrittlement of the spring after electroplating, minor differences in length, etc.

    Which also explains why cantilever brakes, and vee brakes, have provision for adjustment - to equalise the  tensions of, in this case, two separate springs, in order to centralise the arms in relations to the forks.  If you were to measure the valve springs in your car, even new ones, you would find them to be of slightly different lengths, and they would also compress to different heights when loaded with the same weights.

    All the above assumes that your brakes are not binding on the
    pivot bolt, and that your bosses are clean and greased for your vee brake pivots. And that your (front) wheel fits the centre of the forks no matter which way round the wheel is fitted. i.e., that the wheel was built with the rim centred over  the hub, no offset or dish, and having equal spacers each side of the cones.

    Cheers.
     
  5. Vo2

    Vo2 Member

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    Good info, Willie. Difinitely one that I'm going to keep in my knowledge base. ;)
     
  6. Guest

    Guest Guest

    Your'e welcome. Glad to be of assistance. Cheers.
     
  7. Guest

    Guest Guest

    Well, I thought I had this problem sorted out years ago.
    Recently I set up a bike with old Weinmann centre-pull brakes.The front brake was centralised by tapping on the back piece which supports the two arms. Hard road-testing found the front brake quite good, considering it's only acting on a steel rim. But it had moved over, and was starting to rub the rim on one side. Further tapping, but it still came back to rub. Had to think about this one, and the villain seems to be the serrations on the back of the 'back piece', or bridge thing. It has vertical lines, or serrations, designed to make it grip firm, and stay put against the thick alloy spacer which butts up against the fork crown. This spacer is flat one side (to take the brake), and curved on the other (to suit the curvature of the fork crown). The serrations on the 'bridge' had imprinted matching serrations on the spacer, so that the brake would always settle into the old grooves. (And of course the spacer couldn't move or rotate because of the curvature of the crown).
    I thought of two choices: either file the flat side of the spacer smooth again, or put a washer in between the 'bridge' and the spacer. The latter solution seems to have worked a treat, but I'll be keeping an eye on it. Luckily, I was able to remove the brake from the fork crown, only just, to add the washer, without having to detach the cable. It's been many, many years since I've had to fettle centre-pull brakes, that's my excuse.
    I can only assume that the brake wasn't dead central when it was first installed, assuming the current brake blocks are worn evenly. Cheers.
     
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