I think there may be some unfortunate residual mystery about the brake/clutch bleeding process. Often the devices and/or methods used obscure the goal and how to get there simply. This is sad as clutch and brakes should be bled/tested regularly and their fluid changed once every two years, especially in damp climates.
Bleeding, for the uninitiated, is the process of ridding a hydraulic system (clutch or brakes) of entrapped air. Air will prevent the proper performance of these systems. For this example, I will assume that the pumps are themselves primed to the point that they can pump and we are addressing the air in the lines.
uses the bleeders to have the air exit. These little things are threaded
fittings with a passage down the centre to near their bottom where they
exit to the side. The bottoms themselves are tapered and when tightened
they "stopper" the system at that bleeding point. When loosened a bit,
the liquid or air can escape around the taped bottom and into the passage
entrance at the side. A picture to the right
The problem with opening the bleeder and pumping at the pedal is that you will simply pump the hydraulic fluid out and draw in air as the pedal rises back.
Of course, the classic method of bleeding hydraulics leads
to a small toxic mess and the breakup of many families. (sad smile) People
have their wife or children pump vigorously at the brake or clutch pedal
while they wait at the bleeder. This creates pressure in the system...
They then shout to "hold the pedal to the floor" and quickly loosen the
bleeder a tiny bit to open it an allow spray of air and fluid to exit.
They repeat a number of times in hope of forcing the air out. When they
find it hasn't working they divorce the
wife or beat the child and go buy a "device".
None of this is necessary. Air rises in a liquid..use that fact of nature to bleed your system without doubts or fuss. As Bill Button notes, it works..I use Audrey to help when she's around because she even enjoys the process now. She does the job and I have been relegated to pedal pumper.
Simply get a clear glass jar and a small (preferably but not necessarily clear) tube of convenient length (2-3ft) that fits snuggly over the end of the bleeder. "Snug" is sufficient as this system does NOT require high pressure. Fill the jar up a couple of inches with brake fluid, fit the tube over the bleeder and submerge the other end of the tube in the jar.
Now break the seal of the bleeder, and pump the pedal until the bubbles stop. Tighten the bleeder. You've finished. Move to the next bleeder.
You see, since the bleeder, through the tube, is submerged in the jar's brake fluid, it cannot draw in air during the bleeding process and one can actually see and confirm the voiding of the air when the bubbles stop.
WATCH the fluid level in brake and/or clutch reservoir. It will empty as you pump. Keep an eye on their level and add when necessary or you will simply be adding air in the entire system.
Bleed all brakes!! Doing only the rears or the fronts will merely unbalance your brakes. As well, front brake disks have more of an effect than rear drums.
Tightening Bleed Nipples
It is a very common fault to find brake bleed nipples over-tightened (sometimes to the point where they shear or crack the alloy casting). Girling states that "a torque of 4 to 6 lb. ft. should be applied, which is sufficient to lock the bleed screws up without damaging the orifices of the ports. If the orifice has been enlarged and the tell-tale black ring can be seen on the conical seating, then this is a sure sign of over-tightening."
Bleeder Nipples or Valves
Since the brake system is filled with fluid, it must be occasionally "bled". (the old fluid is released in order to install new fluid). This is also done to remove any air bubbles that have gotten into the system (usually when any of the brake parts are changed). All hydraulic brakes have bleeder valves near the slave cylinders. These valves are opened while the brake pedal is pressed, causing the brake fluid to flow out as well as any air bubbles present. When the brake fluid comes out without any air bubbles, the mechanic seals the bleeder valve and tops off the brake fluid reservoir. Bleeder valves can also be found on the side of the master cylinder. These are used for the same purpose; getting air bubbles out of the master cylinder assembly. If you have air bubbles in your fluid, your pedal will feel softer than normal, and braking power will be reduced, so it is a good idea to have your brakes bled properly.
To bleed the brakes, it is easiest to have the tires removed, though it can be done with the tires still on. Ensure that the Master Cylinder supply tank is kept topped up with new (NEVER NEVER USED) brake fluid. This is to ensure that air cannot enter the system through the supply tank.
(Assuming always that your Master Cylinder is properly bled), commence the bleeding at the wheels with the near side rear drum brake if you have drums all around, but if the car has rear drums and front discs, start at the front near side wheel.
With someone at the brake pedal, unscrew the bleed screw one half of a turn or so enough to allow the fluid to be pumped out, and close the screw after the last downward stroke of the brake pedal when the air bubbles no longer appear.
With the bleeder screw open, the pedal should be pushed
by the person at the pedal through the full length of the stroke followed
by three short little fast strokes after which the pedal should be allowed
the rest. This action should be repeated until there is no air and only
fluid expelled. Then it is repeated at each bleeder screw (nipple). (Each
of us has different methods of bleeding the system, many ways will work,
don't choose one that doesn't.