Printable version of Entry

Bleeding brakes:

Everyone natters on about pressure bleeders, using a friend to wear their leg out, yada yada...Here's a method you can do by yourself with nothing more than a length of clear plastic tubing and the appropriate wrenches to open the bleeders.

First, you have to understand that brake fluid is heavier than air, and relatively viscous. Air in the system will want to rise to the highest spot, and it will move along with moving fluid.

Open the reservior cap. Top up the fluid.

Attach the tubing to the bleeder, and drape it so it rises from the bleeder as straight up as you can get it. You want the tube to go up straight so the open end is higher than the reservior.

Open the bleeder.

Wait.

You'll see fluid rising in the tubing all by itself. Gravity is pushing fluid down out of the reservior, and up through the tubing, and will do so until the fluid level in the tube matches the fluid level in the reservior. Fluid seeks its own level.

If there's air in the system, you'll see it bubble up through the fluid. Air rises in brake fluid, so it will go up all by itself. The fluid is moving, which will push the bubbles along in whichever direction the fluid is moving, so eventually all of the bubbles will be transported to the bleeder and out.

Close the bleeder. Top up the fluid in the reservior. Go to the next caliper and repeat.

Now, if you've really drained the system (replaced one or more calipers, or the MC, or lines), you may find that fluid doesn't start to come out on its own for quite some time, so the "Wait." step above may be for a good long while, like an hour. Air is compressing ahead of the fluid in the restrictive passages, and it takes awhile to "blow" the air through the system from the relatively weak push of brake fluid weight. Pumping the pedal with the bleeder open will help a bit here, as the MC will behave like a pump to move the fluid along. Raising the nose of the car can help get fluid to "fall" to the rear calipers a bit faster.

If you have enough tubing and can remove more than one wheel at a time (up on jackstands or the like), there's no reason you can't bleed more than one caliper at a time.

On the prop valve, you might need to crack the upper-most line until you see fluid, then close it again. I've heard people say you need to "mash" the pedal to "open the prop valve", which is wrong. The prop valve is OPEN if there is no pressure in the system (and with significant air, there will be nearly zero pressure). The prop valve CLOSES when there is significant pressure, so mashing on the pedal actually does the reverse of what's desired.

Don't worry about closing and opening the bleeders only with the pedal down. If you have a column of fluid in the tube (as you should just after opening it), then the fluid in the tube will be sucked back in when you lift off the pedal. This is why I've never understood the whole concept of "Speedbleeders", which have a check valve to prevent backflow into the caliper. If there's fluid in the line, where's the air supposed to come from? On some cars with bleeders that fit very loosely, you may find wrapping one turn of Teflon tape around the threads helps bleeding a bit. Air can get past the threads while you're pumping even if the tube is full of fluid. This air will just bloop right out of the bleeder again, but may fool you into thinking the air is coming out of the system. It also helps to not open the bleeder any more than is necessary.

When you get close, you may hear a squeaking noise as you press the brake pedal. This is the sound of a very small amount of air compressing, meaning you just have tiny bubbles left in the system. These very small bubbles often get stuck in restrictive passages, so tapping on joints, loops in hard lines, the MC, the prop valve, and calipers, can help loosen these. Vigorously pumping the pedal can also help.