Front calliper brake – Brompton folding bicycle
Without mudguards, calliper brakes are right in the line of fire for anything your tyre picks up off the road. Dirt ends up on the pivots that hold your callipers together and stops them moving freely. This is one of those satisfying jobs that looks much harder than it is and makes your bike feel much better as soon as you’ve done it.
Like your gears, your brakes are operated by a combination of a cable and a spring. Cables are great for transmitting a signal through all the curves from your handlebars to your brakes and they’re light and strong, but they can only pull, not push. Once you’ve used the cable to pull your brake blocks onto the rim, you release the brake-lever and rely on a spring in the calliper to push the blocks back off the rim so that you can ride and the blocks are back in their original position. However, your hands are generally much stronger than the little coil of wire that does the springing-back job. The effect of this is that, once your calliper pivots start to get all clogged up and sticky, you will still be able to pull your brakes on, but they’ll be more reluctant to spring back away again. Leave it longer still and it will start to be hard work pulling the brake levers on. Luckily, it’s not difficult to clear away the muck and apply a little oil, but the sooner you do it, the more effective it will be. Dirt that’s left long enough will start to corrode the pivots, the washers and the calliper. Once the surfaces that rub against each other become rough and damaged, there’s a limit to how much improvement you can make.
It’s possible to give the callipers a quick wipe over without removing them from the bike, but it’s not difficult to take them off completely and it means that you can really get in properly behind the calliper. An old toothbrush is the perfect size. You can try using plain water if your brakes aren’t too bad, but if you’ve been riding in wet conditions or around town, you’ll probably need something a little stronger. Bike washes like Muc-Off or Finish Line Bike Wash should do the trick. For really stubborn, caked-on dirt – a sign that you really need to invest in mudguards! – try some degreaser. Pour some in a jar then dip the toothbrush in and scrub. Sprayon degreaser is much too messy and wasteful for this kind of
job, where you need precise application. Don’t forget to rinse off carefully afterwards.
As with the degreaser, when you come to lubricate the pivots, drip oil is much better than spray. Take particular care not to get any oil at all on your brake blocks as it will spread all over your rims in no time and you’ll lose most of your stopping power. The gaps that need lubricating are easiest to see with the calliper off the bike. Squeeze the blocks together as if you were squashing them onto the rim and watch how the brake mechanism moves. Anywhere where two sections of calliper move against each other needs the gap between lubricating. After you’ve dripped oil into the gap, squeeze and release the brake unit a few times to work oil into the space and then wipe off excess.
You may find, once you’ve got the calliper off and you’ve started cleaning it, that it’s too corroded to be worth servicing. If this is the case, replace it. You’ll need to get the right size – measure the distance between the middle of the hole that the calliper bolts into and the middle of one of the braking surfaces on the rim. This distance is called the ‘drop’.
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES