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bleeding the brakes

what you'll need:
Time needed: 15 minutes or so
  • A couple of towels to cover the painted sections of your bike
  • 8mm socket for the bleed nipple
  • 1/4" inner diameter clear vinyl tubing (you may have to stretch the very end out with the tip of a #2 philips screwdriver)
  • Bottle for the used brake fluid
  • Philips screwdriver for the master cylinder bracket
  • New DOT 4 brake fluid [NOTE: your bike might take something different! Check your service manual!]

If you do your own mechanics, you'll get pretty familiar with bleeding your brakes, as it'll be part of your routine services. Whisperings of air bubbles and sticking pistons can make bleeding the brakes pretty intimidating the first time, but it's an easy procedure once you understand what's going on, and will eventually take you no time at all. Before you begin, you'll want to cover your gas tank, and probably the front fender, with some old T-shirts or towels. Brake fluid is nasty stuff -- I've personally seen it eat through paint, plastic goggles, styrofoam, and whatever nail polish I happened to be wearing.

None, really. Just insert one end of the plastic tubing into the empty bottle, and have them handy. The SVS has two disc brakes in front, so we'll bleed them one at a time.

First of all, you'll want to locate the bleed nipple on your caliper(s). Each disc that you have has a brake caliper on it, and each caliper will have a bleed nipple. On the SVS, there will be a little rubber cap over the nipple, which itself consists of a screw and locknut. Remove the cap.


Next, use an extended 8mm socket to loosen the nut on the bleed nipple. A little bit of brake fluid will start to come out, so slip the end of your plastic tubing on right away.

bleed_nipple tubing_on_bleed_nipple tubing_on_bleed_nipple2

Here's the fun part. This is easier with a second person, but definitely do-able alone. Finger-tighten the bleed nipple again, so you don't let any air back up into the tube. Squeeze the brake lever a few times, and then hold it in. With the lever held in, loosen the bleed nipple valve again, and watch the fluid come out into the tube. After a few seconds, finger-tighten the valve again, and squeeze the brake lever a few more times. Again, hold the lever in, loosen the bleed nipple valve, wait, close the bleed nipple valve.

If you're completely draining the brake fluid, repeat this relatively monotonous procedure until you're out of fluid (removing the top off of the master cylinder reservoir will speed this along). If you're replacing old fluid with new, simply drain out most of the old fluid. At this point, go over to your other brake caliper, and repeat the entire procedure. Most of the fluid will have already drained out, so you'll probably just have to open and close the bleed nipple valve once or twice.

Again, if you're draining out all of your fluid, keep draining out of that second bleed nipple until nothing more comes out. If you're replacing old fluid with new, open up the master cylinder reservoir, and simply start pouring the new brake fluid in on top of the old stuff. When you see new, clear, fluid coming through the tubing, you know it's gone all the way through. Go back to the first bleed nipple, hook up your tubing, and make sure the new stuff is coming through that brake line as well.

bleeding_brakes master_cylinder

Remove the tubing, close up your bottle of nasty brake fluid (please don't leave it somewhere where it'll spill or animals could get to it), put your master cylinder reservoir cap back on, and use the 8mm socket to tighten up the bleed nipple valves. Don't forget to replace the little rubber caps!

That's it for procdure, but before you close up shop, there's one very important thing you want to make sure of -- that your brakes work. Even though you're seeing fluid come out through the tube, it doesn't mean that the fluid is actually pushing your pistons. After you've tightened everything up, sit on your bike, and just squeeze the brake lever a bunch. You'll be able to tell when the fluid starts to move the piston. Walk the bike slowly forward -- make sure you're not on a decline! -- and try using the front brake to stop the bike. If it doesn't stop, you've probably got an air bubble in the line. Bleed the fluid through a little bit more, and watch the tubing for bubbles. Keep bleeding the fluid until you don't see any. It can get tedious, but you'd much rather be bored while bleeding out air bubbles in your garage than be grabbing your brakes on the road and not have the bike stop. ;)