Bleeding The Brakes - How A Car Works

Remove dirt and corrosion from the bleed nipple with a wire brush , take off the dust cap (if there is one) and put a ring spanner of exactly the right size over the nipple.

Leave the spanner in place and attach a length of clear plastic tubing to the nipple. The tubing should be about 2 ft (600 mm) long, and an airtight fit on the nipple.

Place a clean glass container, such as a jam jar, under the nipple, and put the free end of the tube into it. Pour enough fresh brake fluid into the jar to cover the end of the tube.

Take care when opening the bleed nipple. They are often difficult to turn, and fragile enough to fracture if excessive force is used.

The nipple is made of soft metal and can be damaged easily if the spanner is a little too large.

A corroded nipple can easily break off; if it does, the remains may come out with a screw extractor . Otherwise you may have to buy a new brake caliper or wheel cylinder.

If the nipple does not turn with a reasonable amount of force, put a drop of penetrating oil on the thread and allow a few minutes for the oil to penetrate.

Loosen the bleed nipple about half a turn, and leave the spanner in place. Brake fluid should begin to ooze from the nipple and flow down the tube into the jar. If it does not, the nipple may be blocked, and you must open it (see top right).

When the brake fluid is flowing, ask your helper to pump the brake pedal while you watch the fluid run through the clear tubing. More than a few strokes may empty the master-cylinder reservoir, so remember to keep checking it and top it up if necessary.