|Don't curse the Brembos!
|Mushy Front Brake?
Try Back Bleeding
Thanks to Kurt "PizzaMan" Mirtsching
|Tired of a front brake lever that pulls all the way to the grip? No
amount of conventional bleeding solving the problem?
Back-bleeding is a solution used by auto shops around the
world. Here's how it works.
|Remove the front brake system in it's entirety from the bike, intact. Unbolt
the caliper from the fork, the master cylinder/lever assembly from the
handlebar, and unclip the hose. Don't crack the bleeder or the master
cylinder cap, keep the system shut. Then arrange the system so that the
bleeder nipple is lowest, the part where the brake hose leaves the caliper
is a bit higher, the hose is sloped uphill to the lever, the spot on the
master cylinder where the hose connects is higher still, and the spot on
the inside of the master cylinder where the juice goes in is highest. I
used my vise on my bench and a series of stacked things next to my
bench like cinder blocks, chairs, blocks of wood and what not. Keep in
mind the nasty corrosive nature of brake fluid when choosing things to
put under your brake system.
Get a great big monojet syringe. Agricultural supply places and feed
stores have them. I have one that holds 300cc, which is about five times
what your brake system holds. You want to connect this to your bleeder
nipple, so get clear aquarium tubing or clear PVC tubing at the hardware
store and whatever connectors you need to connect the syringe to the
Fill the syringe with fresh brake fluid, and fill the connected hoses with
fluid too. Attach the hoses to the bleeder nipple. Get ALL the bubbles
out of the tubing and the syringe. There can be air at the plunger end of
the syringe as long as you hold it plunger-up and don't squirt so far that it
enters the hose.
Once all the bubbles are out of the tubing and syringe, crack the bleeder
nipple and gently plunge new fluid into the system. It should push all the
old fluid, and your bubbles, out through the master cylinder. The master
cylinder resevoir will over flow, so have a helper there to suck it down with
another syringe, or have a bunch of rags there to catch the overflow, or
have stuff under the master cylinder that you don't care about.
Some calipers have chambers that can have high internal cavities that
will hold air the way air will stay in an inverted glass underwater. The
bleeder valve SHOULD be the highest point on the inside of a caliper
cavity, but it sometimes isn't. So, as you are plunging the fresh fluid into
the caliper, without letting the hose come off the nipple, roll and rotate
the caliper around so that any internal trapped bubbles can make their
way to the bleeder valve and on out through the brake hose and out the
master cylinder resevoir.
If you run out of juice in the big supply syringe while you're doing this, just
shut the bleeder valve, pull the plunger out, add more juice to the supply
syringe and re-insert the plunger. If you do this right, no air will enter the
hose at the bottom of the syringe, and you can continue to pump juice
through the system.
After you've pumped a bunch of fluid through, shut the bleeder valve and
button up the master resevoir. Clean everything up and re-install on the
bike. If you did it right, and this doesn't do the trick, then you have some
other problem, such as a faulty hose that's expanding, a warped disc, or
bad rubber in your master cylinder or caliper.
Keep in mind that fresh pads sometimes need to "take a set" or break in.
They don't exactly mate with the disc and have to rub off just a bit of
material. Riding 100 yards with your brake held on can accomplish this.
Brand new pads that need to take a set feel just like air in the line.