How to Bleed Your Brakes

a corral original article
Christopher Ihara
 

CORRAL UNIVERSAL RATING SYSTEM:
Difficulty (Easy 1-10 Difficult) Very Easy
Special Tools (Few 1-10 Many) None
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Quality (Poor 1-10 High) N/A
Improvement (None 1-10 Alot) Alot
Customer Service (Poor 1-10 Good) N/A

Potentially the most neglected system on any Mustang is the brake system. Most people spend dozens of hours gapping spark plugs, adjusting fuel pressure, bolting on lots of go fast goodies, and changing the oil; however, hardly anyone bothers to change one of the most important fluids in the car -- the brake fluid.

While most people find them terribly boring, your Mustang's brake system is one of the most important and neglected systems. Sure, a new set of pads and shoes are stuck on every once in a while, and some people even go so far as to order trick dimpled or slotted rotors. Very few people, however, bother to change the brake fluid. This process isn't listed as a regular service item in any manual. It isn't even done by any mechanic who performs brake services on your car unless you specifically ask to have the service done.

"Why is this so important?" you may ask. First we need to understand a few things about how a braking system works, and what brake fluid does. If you'll recall from basic physics and chemistry the Law of Conservation of Energy which states that, "Energy cannot be created or destroyed, but can change its form." When you romp on the gas pedal and accelerate the car you are using a certain amount of energy to get the car up to speed, building up its kinetic energy. So if you've used 250 horsepower to get up to speed in six seconds, you'll need to lose almost that much horsepower to stop.

When you want to slow down you need to get rid of all that kinetic energy. So you press on the brake pedal, fluid is pushed out to the brake pistons in the calipers and they, in turn press the pads against the rotor surface, which creates friction. The force of the Mustang's acceleration turns the brake rotor which is now being clamped by the pads. Remember the Law of Conservation of Energy? ("Energy cannot be created or destroyed, but can change its form.") As the rotor turns and rubs against the pads the friction turns the car's kinetic energy into heat, thus slowing the car down. So basically your brakes are giant heat sinks which serve to dissipate heat.

The more your car weighs and the faster you go, the more energy it takes to get your car off the starting line, and also to stop it. The more energy it takes to stop your car, the more heat that will be generated during the braking process. So if you've got a car full of your friends your brakes will generate a greater amount of heat during braking than if you are travelling alone. It is not uncommon for brakes to get up to several hundred degrees in temperature with moderate to heavy use. Road Race cars often see temperatures high enough to make the brake rotor glow in broad daylight.

What does all this have to do with brake fluid? Remember all that heat that we built up when we hopped on the brakes? A lot of that heat transfers into the braking components of the car, in particular the calipers. Inside the calipers is brake fluid. With several hundred degrees surrounding the caliper, the fluid inside can acutally boil in this miniature oven.

Since brake fluid must put up with these extreme temperatures, it is designed to withstand high boiling points. Most brake fluids don't boil until they reach around 350 deg. Farenheit, some go as high as 550 deg. Farenheit or more! When heated to its boiling point though, brake fluid will boil just like water. When this happens air escapes from the fluid and gets trapped in the brake lines. If you've ever experienced a very spongy brake pedal, chances are you may have boiled your brake fluid. So when you press on the brake you're no longer pressing against brake fluid (which can't be compressed), you're pressing on air (which compresses very easily).

In addition to transferring pressure from your foot to the calipers, brake fluid serves to protect the braking system from corrosion. Water vapor in the air can mix with the brake fluid by entering in through any number of places: the reservior cap, bleed screws, hose junctions, pistons, etc. Water inside the braking system can wreak havoc, it can corrode and rust brake lines and calipers rendering them inoperable or ineffective at best. For this reason brake fluid is hygroscopic, meaning that it absorbs water. It does this to help keep water away from the metal parts of the brake system. By doing this it keeps the components from rusting.

The idea behind bleeding the brakes is to remove any air and old fluid from the system. Good brake fluid should be a "honey" color and should have the consistency of light oil. It should NOT be "watery" or look like coffee! Generally the more water the fluid has absorbed the more "coffee-like" its appearance.



TOOLS SECTION
  • One Man Brake Bleeder Kit or 1 Liter Soda Bottle with cap
  • 3' of 1/8" inside diameter clear plastic tubing
  • Adjustable Wrench
  • Jack
  • Jack Stands
  • Breaker Bar or Lug Wrench for removing wheels
  • Three Cans of Ford Heavy Duty Brake Fluid
  • First you'll want to pick up a few items. If you are planning on doing this yourself, you'll need a one man brake bleeder kit, which you can get from your local auto parts store for about $10-20. If you've got help you'll need some clear plastic tubing, about 3' should be more than enough. It will need to be about 1/8" inside diameter, big enough to fit on to the bleeder screw nipples, but tight enough to keep fluid and air out.

    Next you'll need lots of brake fluid. Ford Heavy Duty Brake Fluid is HIGHLY recommended and you can get it from any Ford parts counter. We've used it in race cars and in street cars, it has a high boiling point, provides relatively long life before it needs to be changed, and best of all it is CHEAP. Performance is about as good as some of the more expensive racing brake fluids and you can get this for about $5/container at the dealership. Get at least three.

    You'll also want some kind of container to drain the old fluid into. 1 Liter soda bottles work great because they have a screw cap. Get a couple of these. PLEASE DISPOSE OF USED BRAKE FLUID PROPERLY!

    Make sure that when you're doing this that YOU DO NOT GET BRAKE FLUID ON THE PAINT!!!! It will eat the paint off your car! Also be sure not to let fluid get on the brake pads.

    First, put the car up on jack stands on a LEVEL surface.

    Remove all the wheels.

    The order of bleeding should go like this:

    • Always start bleeding from the wheel that is FARTHEST away from the master cylinder. On a Mustang this is the Passenger side rear wheel.
    • Next, do the Driver's side rear wheel
    • Now do the Passenger side front wheel
    • Finally bleed the Driver's side front wheel.

    There are two procedures that you can follow, one is if you've got a brake bleeder kit, the other is if you have a helper.

    ONE MAN BRAKE BLEEDER KIT

    1. Remove the brake fluid reservoir cap.

    2. Fill the kit's refill bottle with fresh brake fluid and install it's cap. You will put this on the master cylinder once most of the fluid has drained out of the master cylinder.

      Click to enlarge
    3. Attach the bleeder hose and catch bag unit to the passenger side rear bleeder screw.

    4. Slowly and carefully open the bleeder screw until brake fluid begins to seep out into the tube.

    5. Pump the brake pedal until the master cylinder reservoir is ALMOST empty, BUT DO NOT LET IT RUN OUT OF FLUID! There should be about 1/4" of fluid above the bottom of the brake fluid reservior.

    6. Quickly and carefully invert the refill bottle and set it into the neck of the reservoir. It should balance OK, but you may need to secure the bottle in its inverted position with tape. As the fluid from the reservoir drains, the refill bottle will replenish the supply until the brake fluid reaches the top of the reservoir. At that point the refill bottle will stop filling automatically.

    7. Pump the brake pedal until the refill bottle is empty, BUT DO NOT LET THE MASTER CYLINDER RUN OUT OF FLUID! If you do you'll have to start all over again!

    8. Refill the brake bleeder kit refill bottle and continue the process until CLEAN, CLEAR, "honey" colored fluid starts coming out of the rear caliper.

    9. When this happens, close the bleeder screw and remove the catch bag and hose. Make sure not to overfill the catch bag! If you need to empty it, CLOSE THE BLEEDER SCREW FIRST, then lower the bag below the caliper and remove the bag's hose.

    10. Repeat steps 4 - 8 on the driver's side rear wheel, then the passenger side front wheel, finally on the driver's side front wheel.

    11. When you have completely bled all the brakes, reinstall the master cylinder cap, install and torque all wheels, and dispose of brake fluid properly. Check with your local shop for this, they may have a recycling bin that you can depost used brake fluid into. PLEASE DO NOT simply throw away your old fluid, or dump it on the ground.

    BLEEDING WITH A HELPER

    1. Remove the master cylinder cap.

    2. Attach your clear hose to the brake caliper bleeder screw.

    3. Put end of bleeder tubing into 1 liter bottle on the passenger side rear bleeder screw.

    4. Pump the brakes five times and hold pressure on the pedal.

    5. Your helper should slowly and carefully open the bleeder screw until brake fluid begins to seep out into the tube.

    6. When the pedal reaches the floor, keep it pressed to the floor and tell your assistant to close the bleeder screw.

    7. When the screw is closed, go back to step 4.

    8. Continue this process until the Brake Fluid Reservoir is nearly empty, BUT DO NOT LET IT RUN OUT OF FLUID! If you do you'll have to start all over again! If you have ABS this can let air into the ABS module and then you'll have to go to the dealer to have it removed.

    9. Refill the brake master cylinder, and continue steps 4 - 8 until CLEAN, CLEAR, "honey" colored fluid starts coming out of the rear caliper.

    10. When this happens, close the bleeder screw and remove the tubing.

    11. Repeat steps 4 - 10 on the driver's side rear wheel, then the passenger side front wheel, finally on the driver's side front wheel.

    When you have completely bled all the brakes, reinstall the reservoir cap, install and torque all wheels, and dispose of brake fluid properly. Check with your local shop for this, they may have a recycling bin that you can depost used brake fluid into. PLEASE DO NOT simply throw away your old fluid, or dump it on the ground. When you have finished either of these processes, be sure to start the car and pump the brake pedal a few times with all bleeder screws closed. Check for leaks and make certain that you have good pedal feel. If the pedal is even more spongy than before you have let air into the system and will have to bleed the brakes to get the air out.

    This process should take you no more than a couple of hours for your first time. It is a maintenance item that you should do at least once every two years to ensure that your braking system will be up to optimal operating capacity the next time you really need to use it. This two hour investment could save the front end of your Mustang.


     
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