Boxster Project: Brakes: Bleeding and Flushing

The basics for bleeding or flushing brake fluid:

• an assistant, or Speed Bleeder screws, or a Power Bleeder (see [ Parts ] )
• a box wrench that fits the bleeder screws (3/8" for the Speed Bleeder screws, 11mm for the stock screws)
• new fresh brake fluid
• surgical tubing to bleed the fluid out into a bottle
• a resealable bottle or can to hold the old fluid
• disposable gloves and shop rags to protect yourself and the car from brake fluid

Bleeding and flushing operations push the old fluid out of the brake lines. Bleeding lets a little out and you top up the reservoir with fresh fluid; flushing is a complete replacement, where you push all the old stuff out and completely replace it with the fresh stuff.

The preferred order of work when flushing is Right Rear, Left Rear, Right Front, Left Front. This works the corners farthest away from the master cylinder first. But the order is not really crucial.

You can also bleed or flush the clutch master cylinder, since it's all part of the same single hydraulic system. But the bleeder screw for it is extremely difficult to reach. I haven't done it myself so I won't describe it here.

Siphoning the Reservoir

If you are doing a complete flush, things will go faster if you first siphon off the excess of old fluid from the reservoir. Unscrew the reservoir cap and remove the filter screen with a pair of tweezers or pliers. You can use a turkey baster to suck out as much fluid as possible from the reservoir and put it into the used fluid container. Don't put the baster back in the kitchen when you're done. You really don't want to ingest any brake fluid. Top up the reservoir with fresh fluid, or if you're using a Power Bleeder, fill up the pressure bottle and hook it up according to its instructions.

One thing you don't want to do is to take so much fluid out of the reservoir, that you cause air to be sucked into the lines. Then you'd have to flush the entire system again.

If you're just bleeding the system, not flushing, then don't drain the reservoir -- you'll just be topping it up as you go. If you're using a Power Bleeder to bleed (not flush), this is also where you fill it up, pump it up, and attach it.

Now, on to what to do at each successive corner of the car.

1. Remove the little rubber cap from the outer bleeder screw on the caliper. Attach one end of the surgical tubing hose to the screw and make sure it's snug. Make sure the other end of the hose leads to your bottle that will contain the used fluid.

2a. Using Speed Bleeder Screws: Using the 3/8" wrench, open the bleeder screw 1/4 turn counter-clockwise. Get in the car and press and release the brake pedal several times. About 5 times will be good for a bleed. For a complete flush it will take a lot more, and it will be easiest to gauge if you can see the fluid change color (from Ate Gold to Ate Blue) to know when all the old stuff is gone. For a bleed, at 5 pumps of the pedal, you will have plenty of fluid left in the reservoir to be sure that it won't drain so low as to introduce air into the system. For a flush, at 20+ pumps of the pedal, you'll want to take a look at the reservoir after 10 or 15 pumps to see how fast the level is going down. In either case you'll want to top up the reservoir before it gets too low. The reservoir at full contains way more than enough fluid to let you bleed both screws on the caliper with 5 pumps of the pedal. Bleeding one corner may not even deplete half the reservoir. So for a bleed you can bleed both screws and then top up the reservoir. When you're done, close the bleeder screw back 1/4 turn clockwise to where it was.

2b. Using a Power Bleeder: Using the 11mm wrench, open the bleeder screw 1/4 turn counter-clockwise. Watch the pressurized fluid come out until you've either bled the desired amount, or flushed all the old fluid out. Again, if you are bleeding and can transition from Ate Gold to Ate Blue, you'll see when the new fluid appears. When I went from Blue to Gold, it was a little hard to see because the surgical tubing had become blue-stained and it seemed like the fluid color changed gradually. When you're done, close the bleeder screw back 1/4 turn clockwise to where it was.

2c. Using an assistant: Using the 11mm wrench, open the bleeder screw 1/4 turn counter-clockwise. Say "down" to signal the assistant to push the brake pedal down. Watch some fluid come out. Have the assistant say "OK" when the pedal is all the way down. Close the screw back 1/4 turn clockwise to where it was so that air cannot be sucked back in. Say "up" to signal the assistant to release the brake pedal back up. Have the assistant say "OK" when the pedal is all the way up. Open the screw. Say "down". Assistant presses pedal. Fluid comes out. "OK." Close the screw. "Up." "OK." Open it. "Down." "OK." Close it. "Up." "OK." Open. Repeat ad nauseum until you are done. Check the reservoir and top it up; if you're flushing the system, you will definitely need to keep it topped up as you work on the first corner.

3. When you've finished the outer bleeder screw and it's been closed for the last time, carefully pull the hose off, using a rag over the end to contain any dripping or splatter of fluid as it comes off. Put the little rubber cap back on.

Repeat the process for the bleeder screw on the inner side of the caliper. This one will only need a little bit of fluid extracted, because you've already cleaned out the entire brake line from the master cylinder to the caliper, and the old fluid is just in the short section around the caliper that branches away from the brake line. When I bleed with the Speed Bleeder screws, I do 5 pumps on the pedal anyway.

Press the brake pedal a couple of times to make sure it's firm.

Wipe up any drops of fluid that have found their way onto the caliper or floor. Press the brake pedal a couple more times to make sure it's firm. You don't want to find out you forgot to close the bleeder screw when you come to an intersection and have no brakes!

Take the used fluid to a proper place that accepts it. In my area, Kragen took motor oil but not brake fluid. Pep Boys took the brake fluid.

OK, you're done with the fluid, and are ready to go back and finish up with [ Replacing the Wheel ].