Chapter 7

Performing a Bleed


Brake fluid containers feature a warning label. Read it. Be especially careful when compressing the syringe. If the clear plastic bleed hose blows off the bottom of the syringe, getting fluid in your eyes is very painful to say the very least.

1) Loosen the cable (see Chapter 2).

2) Determine pad wear (see Chapter 5). Combining pad replacement with fluid replacement can be a good thing.

3) Adjust the brake pads (to attain optimal performance, the pads should be properly adjusted BEFORE bleeding the system-see Chapter 4).

4) Attach the slotted brass fitting with the knurled nut onto the Formula syringe.

5) Draw in 10ml of brake fluid from the brake fluid container. DOT 5.1 is recommended (see Chapter 10).

6) Disconnect the hydraulic line where it enters the caliper. The red part should stay with the caliper but the silver part should remain with the hydraulic line. Note: Because the master cylinder and the caliper are both self-sealing (there are spring loaded check-valves within the red anodized connectors), these pieces won't leak when you disconnect the hydraulic line. The hydraulic line itself, however, can weep a bit when you disconnect one end, and will drain completely if both ends are disconnected. Therefore the bleed process is typically a bit neater if you always leave one end of the line connected. One warning: if after you disconnect the line at the caliper (per the above instruction) someone squeezes the brake lever, your disconnected brake system becomes a toxic squirt gun. When working in an area where someone might squeeze the brake lever, the recommended process is to disconnect both ends and catch the fluid seepage in a rag or hand full of napkins.

7) Thread the brass fitting onto the red fitting of the caliper body.

8) Use your 5 mm Allen wrench to remove the caliper from the mounting bracket. Note: If you use your 5 mm Allen wrench to remove the horizontal mounting bolts instead of the 4 mm Allen wrench to remove the vertical mounting bolts you won't have to readjust the angle of the caliper when you reinstall it. Further, watch for any washers, as you'll need to replace them in the same position.

9) The caliper should now be free of the bike and dangling from the half-filled syringe. With the red fitting of the caliper pointed upward and the syringe held above it, use a downward stroke to compress the pads until they touch each other. Continue pumping up and down with the syringe to extract fluid with bubbles and pump in fluid without bubbles. Tapping the caliper with the backside of your screwdriver will loosen bubbles that would otherwise stick in the comer of an internal cavity. With enough pumping, tapping and other gyrations, you should finally get to a point where no more bubbles appear on the upstroke. Congratulations! You have successfully bled the caliper. With experience, you can do this in 60 seconds.

10) Reinstall the caliper onto the frame.

11) Remove the syringe from the caliper and reattach the lower end of the hydraulic line.

12) Remove the slotted brass assembly off of the syringe's clear plastic bleed hose and replace it with the threaded one.

13) Use a 4 mm Allen wrench to remove the bolt securing the master cylinder to the down tube.

14) Use a 3 mm Allen wrench to carefully remove the master cylinder's bleed screw. Warning: the bleed screw tightens against a small rubber 0-ring which occasionally becomes stuck to the bleed screw's pointed end. Watch for it. Don't lose it. If, when you remove the bleed screw, you don't see this 0-ring, that's good news - it stayed seated at the bottom of the bleed port.

15) Fill the syringe with 20ml of DOT fluid and thread it into the port where you (moments earlier) removed the 3 mm bleed screw.

16) Use a screwdriver to remove the slotted vent screw at the top of the expansion chamber. Insert the 6mm white, nylon bushing (or a 1/4" ball bearing) in the chamber. And replace the slotted vent screw.

17) Using the same pumping, tapping and gyrating method you successfully learned earlier, remove all vestiges of air from the master cylinder. In this case upstrokes and down strokes will push the float up and down in the expansion chamber, creating movement of the fluid past the bleed port separating the pump's two chambers (the expansion chamber and the wet side of the piston). While it takes longer to successfully bleed the master cylinder than the caliper, a pro can do this in 120 seconds.

18) Attach the large, clear plastic bleed hose to the bleed valve on the caliper unit. The other end of this hose will be placed in a container to catch excess fluid.

19) Depress the plunger of the syringe lightly while reattaching the hydraulic line to the master cylinder.

20) Continue to maintain light pressure on the syringe while opening the bleed valve one-quarter turn.

21) Slowly pump 10ml of brake fluid into length 7-8 ml of brake the hydraulic line will be expelled through the caliper. Note: While it might seem stupid to pump air through a caliper you bled a few minutes ago, it is easier for the air to exit by way of the bleed valve than it will be for it to fight its way into one of the fluid- filled cavities behind the pads. If you want to worry about air from the hydraulic line reaching these areas, raise the front end of the bike so that the bleed valve and red fitting are above the pads.

22 SNUG the bleed valve.

23) Holding the master cylinder so that the bleed port is pointing upward, remove the syringe from the master cylinder.

24) Use three or four drops of brake fluid to overfill the port where you just removed the syringe-

25) Through these excess drops reinstall the pointed bleed screw into the master cylinder - do not over-tighten-and wipe away the excess fluid.

26) Reattach the master cylinder to the frame.

27) The final step is to remove the white, nylon bushing from the expansion chamber and replace the slotted vent screw.

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