Technic

Brake bleed procedure

1. Installation notes

1.1. Use a high performance ethylene glycol based fluid such as Castrol Racing Fluid or, for higher temperature use, Castrol SRF. Do not use silicone brake fluid. Brake fluid is hygroscopic and the boiling point will reduce if it contains any moisture. For optimum performance, fluid should be changed regularly.

1.2. Each Alcon brake caliper has an optimum mounting angle, normally within plus or minus 5° of vertical, to prevent air from being trapped in the piston bores. Check with Alcon’s technical department if the angular position is greater than 5° from vertical.

1.3. Ensure that the master cylinders are firmly fixed to a rigid bulkhead or cross member.

1.4. To avoid trapping air in the master cylinders, ensure that the fluid outlet port is uppermost. Preferably mount the cylinders level or with the push rod end slightly lower.

1.5. Avoid vertical loops in brake lines, which will trap air, particularly in the feed from the reservoir to the master cylinders.

1.6. To prevent a vacuum forming in the reservoir, there must be a breather hole in the cap.

Let It Bleed

To properly bleed the brakes, start with a couple of 8-ounce cans of fresh brake fluid. An unopened can has a long shelf life. An opened can should be discarded within a few weeks. Get the vehicle up in the air and remove all four wheels. Well, okay, you might be able to do this with the wheels on if you can swing a wrench on the bleeder valves.

If you can't turn the bleeders without breaking them off, you'll need to replace the brake calipers or wheel cylinders. See the above notation about penetrating oil and light hammer taps before applying enough torque to break these minuscule, hollow bolts.

Sneak into the kitchen and appropriate the small turkey baster. Remove the top to the master cylinder reservoir and suck out as much of the old squid ink as you can. Clean any sediment out of the reservoir with a clean, lint-free rag. Do not spill any brake fluid on any painted surfaces -- it will remove the paint pretty much immediately.

Get a piece of clear plastic tubing (aquarium tubing is fine, and it's cheap). Push one end of the tube over the brake bleeder bolt at the right rear of the car. Put the other end of the tube into a small, clear bottle with an inch or two of clean brake fluid in it. (This will keep air from being sucked back into the brake cylinder or caliper.) Put a piece of 1 x 4 lumber or some other spacer under the pedal to prevent the pedal from traveling too far when line pressure is released. Top off the master cylinder reservoir with fresh fluid and put the cover back on the reservoir. Fluid will squirt out of an open reservoir every time the pedal is released.

Cue the Helper

Your helper needs to be someone who can follow instructions exactly. He or she won't get dirty hands so you don't need to pull one of your pals away from the ballgame. A teenager in a white dress will do fine. Have your helper sit in the driver's seat and await your orders. Here's the drill: You say "down." He or she depresses the brake pedal with about the same amount of force needed to keep the car from rolling forward at a traffic light. Then your helper says "down" and keeps the pressure on. When you hear the call, warn your helper that the brake pedal is about to sink underfoot and to keep the pressure on constantly. Then crack the bleeder bolt a quarter-turn.

A bleeder bolt can become difficult to remove. Use a proper-fitting box wrench to keep from rounding it off.  Got ABS? You may need to use a scan tool during the bleeding process to cycle the pump and valves.

Some of the old, contaminated fluid will trickle down the tubing into your bottle. When the trickle stops, close the bleeder. Then you say "up." Your helper says "up," and removes his or her foot from the pedal.

Repeat this process until fresh, clear fluid comes from the bleeder. Any out-of-sequence moves can suck air into the caliper. Yes, the end of the tubing is submerged in fluid, but air can travel past the threads on the bleeder bolt into the caliper if there's ever any negative pressure in the system while the bleeder is cracked.

Every half-dozen or so iterations, top off the reservoir with fresh fluid. Do not allow the reservoir to get more than half empty -- air can be sucked into the master cylinder unless the fluid level remains well above the bottom of the reservoir that feeds the cylinder.

Once clean fluid is coming out of the brake, snug the bleeder bolt and move your operation to the left rear wheel and start all over again. Next repeat the process with the right front and finally with the left front. Follow that with a few strokes of fresh fluid from all four, again. Don't forget to keep the reservoir topped off.