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Bleeding Brakes

Easy, effective preventive maintenance

Created by Mac Demere

Brake bleeding is one of the easiest, cheapest, and most effective forms of preventive maintenance for the do-it-yourselfer. Done every two years, completely renewing brake fluid will not only help ensure maximum stopping power but also will extend the life of internal brake components. Another advantage: Brake bleeding will indicate when a major brake rebuild is necessary.

Critical Care

I learned the value of regular brake bleeding when I was racing and encountered badly fading brakes. Blasting into a 65-mph turn at 130 with ineffective brakes is not nearly as much fun it sounds. I was baffled as the brake pads and rotors had been freshly serviced. In desperation, I bled the brakes. Out squirted a dark, bubbly mess reminiscent of a misadjusted soft-drink dispenser: mostly cola syrup but a bit of carbonated water. Racetrack braking had raised the temperature of the brake fluid to nearly 300 degrees. This caused the brake fluid to break down and release vapors. Also, the moisture that the brake fluid inevitably sucks out of the air boiled and added more air pockets, so the system wasn’t fully pressing the brake pads against the rotors. Bleeding the brakes before every on-track session became a ritual.

Two or three years of aggressive mountain road driving, hauling heavy loads, or battling dense urban freeway traffic may similarly degrade your brake fluid. Also, the moisture that brake fluid naturally pulls out of the air not only reduces emergency stopping power but also encourages corrosion of internal brake parts. This corrosion tears rubber seals and ruins the expensive parts inside anti-lock braking systems. Another benefit of bleeding brakes: If the old brake fluid contains bits of rubber and other flotsam, you know a complete brake job is required.

To bleed the brakes, use a wrench to twist open a valve that looks like, and is often called, a nipple. It’s located on the brake caliper, or for drum brakes the wheel cylinder, and is covered by a rubber cap.

The Tools

Here’s what you need to bleed brakes:

Two or three small bottles of brake fluid. (Don’t buy the large containers: Once brake fluid is opened, it must be used or taken to the recycler.)

Someone who will precisely your follow directions. (Hint: A spouse or romantic interest is a poor choice. A teen hoping to drive this car may be the best.)

Jack, tools to remove wheels, at least one real jackstand (not a cinder block or stump!), and something to use as wheel chocks

Combination box-end/open-end wrench that fits the nipple (a good auto parts store will be able to tell you the proper size)

Length of clear plastic hose that fits tightly over the brake nipple

Safety glasses because the hose will inevitably pop off and fluid will spray everywhere

Clear plastic container

Container to collect used fluid and take it to the recycler

Rags, paper towels, and kitty litter to clean up the inevitable mess. (Keep pets and children away from spilled fluid and brake fluid containers!)

Can of brake parts cleaner to clean spilled fluid from rotors or calipers.

Step-by-Step Process

Here is the procedure. (Please take all safety precautions. A single trip to the emergency room costs more than a lifetime of professional brake bleeds.)

Step 1: Chock one front tire, both front and rear, with bricks or wood blocks so the car can’t slip off the jack.

Step 2: Jack up the right rear of the car, remove the right rear wheel and set the down car on the jackstand: Do not rely on the jack alone! (If you have multiple jackstands, you can remove as many wheels as you choose.)

Step 3. Make sure the master cylinder reservoir, found in the engine compartment, is full. Repeat this check regularly: Running the master cylinder dry will significantly lengthen the process.

Step 4. Find the bleeder valve. It looks like a nipple and should be covered by rubber piece that looks like a ball cut in half. Remove the cover and place it where you can’t lose it. The time between when I store the cover in a secure position and when it disappears forever can’t be measured by modern science.

Step 5. Slip the box-end portion (the part that makes a complete circle) of the wrench over the nipple. Slide the plastic tube over the nipple and run it into the clear plastic container. Clear tubes and containers allow you to inspect the exiting brake fluid.

Step 6. Tell your assistant to smoothly press down on the brake pedal and hold it down. Emphasize smoothly. Aggressive pumping will turn large air pockets into difficult-to-remove tiny bubbles. (If you suspect there’s a lot of air in the system, have the assistant smoothly press and release the pedal two or three times before holding it down.) When assistant is firmly holding the pedal down, have him shout “Down” and—this is important—keep firm pressure on the brake pedal as it moves toward the floor.

Step 7. Open the bleeder valve by turning it about a quarter to a half turn counter-clockwise. You’ll know when the valve is open far enough when brake fluid squirts out. After no more than one second, immediately tighten the nipple. Inspect the fluid that comes out. (At this point you can switch to the open-end side of the wrench if it makes things easier.)

Step 8. When the valve is closed tight, shout “Up.” The assistant should smoothly release the pedal and respond “Up.” (Sooner or later, even the best helper will be “up” when they should have been “down.” It’s not disastrous: You’ll just have to do a bit more bleeding.)

Step 9. Again shout “Down.” When the assistant responds “Down,” open the valve as in Step 7. Then retighten the valve and shout “Up.” Your assistant must respond “Up.”

Step 10: Replenish fluid in the master cylinder reservoir.

Step 11: Repeat Steps 6 through 10 until you believe fresh fluid has reached that wheel AND the fluid runs clear and free of bubbles. If bits of rubber or flotsam flows out, a major rebuild is in your near future. Do not over tighten the bleeder. Replace the rubber bootie if you can find it. (You can’t. Go buy a new one.)

Now you’ve bled one wheel. Only three more to go. Do the left rear next. Then the right front and finish with the left front. Front brakes provide about three-quarters of stopping power, so you want to ensure they have completely fresh fluid.

Finishing Tips

After you’ve bled all four wheels, have your assistant press the brake pedal while you look for leaks. The brake pedal should be firm. If it mushes toward the floor, either you did something wrong (like under- or over-tightening a bleed valve) or you’ve got another problem: Likely culprits are a leaking master cylinder, cracked brake lines, or failing caliper seals.

A warning about brake fluid: It’ll eat the paint or finish off many surfaces. If you spill some on bodywork or painted wheels, wash it off immediately. Avoid laying brake-fluid-soaked rags on fenders or touching paint with fluid-contaminated hands. Check with your local recycler for proper recycling procedures.

There are several “one-person” brake bleeder kits on the market. Good ones are expensive, require compressed air and are intended for professionals. There are also one-person hand-pump vacuum systems. Racers, autocrossers and track-day drivers should consider replacing original-equipment bleed valves with aftermarket valves that employ one-way check valves. These cost about $25 for a set and eliminate the need for a helper. The mechanic opens the bleeder as normal, but the check valve prevents fluid from exiting or air from entering. Then the mechanic acts as his own assistant and presses on the brake pedal: old fluid and air bubbles exit but the check valve prevents anything from reentering. When done, the bleeder is retightened.

One more note about bleeding: If you have a manual transmission, both the clutch master cylinder and slave cylinder need regular bleeding, too.

About the Author

Mac Demere is a vehicle tester and race driver who competed in the NASCAR Southwest Tour and Daytona 24 Hours.