Tuesday, April 3, 2012

Brake Bleeding

While I was cleaning the VTR, I also took the opportunity to bleed the (front) brake. I observed that the brake fluid, in the reservoir site glass, was the color of maple syrup. That color usually indicates old fluid and old fluid usually has a higher water content than is recommended. Chapter 15 - Hydraulic Brake (on the Resources page) outlines the brake fluid replacement procedure as well as the air bleeding procedure. If you have a power bleeder, the instructions are on page 15-3 (and you won't need to even bother reading this). If you do not have a power bleeder and will be bleeding "old school", I base this procedure on the instructions under AIR BLEEDING which are found on page 15-4. Note: I would suggest reading through the procedure, first, to become familiar with it and tools/supplies needed.

Tools/Supplies needed:

  • Fresh DOT4 brake fluid
  • Brake Cleaning fluid
  • Paper towel or rags
  • Rubber band or long twist-tie or long zip-tie
  • Medical syringe (without needle) or paper towel/rags/old sponge
  • 8mm box end (bleeder) wrench
  • 12" (approx.) of clear 1/8" I.D. hose
  • Container for old brake fluid - small glass juice bottle or used oil container
  • Phillips head screwdriver

(btw, I totally forgot to take any pictures - sorry).

There's no sense in bleeding all of the old fluid through the brake line and the caliper. So, we'll remove it instead. Note: you'll want to ensure that the brake lever is not moved while draining the reservoir. If necessary, place something between the lever and the grip to keep the lever from moving.

  • Orient the bike so that the bake fluid reservoir is level. You may be able to do this by rotating the handlebars in a certain way or you may have to use a chock or lean the bike against a wall.
  • To prepare the reservoir for bleeding, I fold up a piece of paper towel, length-wise, so that it's about 1" - 2" wide. I wrap this around the reservoir and hold it in place with a rubber band. Place the paper towel wrap so that it's just under the lid. This "wrap" will hopefully prevent any brake fluid from running down the side of the reservoir and dripping on the controls or on the bike's paint (fyi - brake fluid will remove paint very quickly).
  • Remove the lid from the reservoir. You'll need a Phillips head screwdriver. In addition to the lid, there will be a plastic backer and then the rubber seal. There will most likely be brake fluid on all three parts. Place them on a rag or piece of paper towel yet keep them handy (as we'll need them in a moment).
  • I use a medical syringe to remove as much of the old fluid as I can (fyi - syringes, without needles, are usually available at any drug store or medical supply store - if you cannot source a syringe, you can use paper towel or an old sponge). Brake fluid is considered hazardous waste. I place the used fluid into a glass container (juice bottle) but a used oil container would work, too. Since most brake fluid reservoirs have a low spot, it's inevitable that there will be some fluid left. I then use a piece of paper towel to absorb the remainder.
  • At this point, fill the reservoir with fresh DOT4 brake fluid (the shop manual will recommend that the can be new/sealed).  There's a fill line cast into the inside of the reservoir. Replace the rubber seal, backer and lid. Secure the lid with the two screws.
  • Remove the bleed screw cap/cover. Place the bleeder wrench over the bleed nipple on the caliper. Place the clear bleed hose on the bleed nipple. Route the open end of the hose into the container with the old fluid. Place the container so that it's close to but lower than the caliper (we want the fluid to drain into the container).
  • Kneeling in front of the front wheel, use your left hand to reach up and apply pressure to the brake lever. Hold the lever to maintain pressure. With your right hand, crack the bleeder screw open (a quarter turn is usually enough). Old fluid should appear in the hose and the lever should move toward and impact the grip. Hold the lever in place (at the grip) and tighten the bleeder screw. Release the brake lever. You have now pushed old fluid out of the brake line/caliper and sucked in new fluid (from the reservoir). Repeat this step until the fluid coming out of the bleed nipple is clean/clear. Note: you will probably need to repeat this step between five and ten times. However, the reservoir may not have the capacity to bleed the line and the caliper without a refill. Keep an eye on the site glass after every bleed step to ensure you do not run the reservoir dry (if you do, you'll suck air into the line and/or caliper and that's not good). When you see the brake fluid level in the site glass, refill the reservoir.
  • When the brake fluid coming out of the bleed nipple is clean/clear, tighten the bleed screw, remove the bleed hose and remove the bleed wrench. Use paper towel to absorb any fluid on/around the bleed screw (a shot of brake cleaning fluid will do the same thing). Replace the rubber bleed screw cap/cover.
  • Top off the reservoir (to the fill line cast into the inside of the reservoir) but do not overfill. Replace the rubber seal, backer and lid. Secure with the two screws. Wipe away any excess brake fluid with paper towel and/or brake cleaning fluid. Ensure that you have good pressure when squeezing the brake lever.

Depending on your use of the bike, you should be good for the next riding season or two.

No comments:

Post a Comment