San Diego Miata Club

Bleeding the Brakes

Submitted by Robert "JTBob" Holland


This job is very simple, but requires the help of one or two other people. You need the following items: DOT 3 or DOT 4 brake fluid (a quart is more than enough, do NOT use DOT 5), 8 mm wrench, a clear bleed tube (about 1 to 2 feet long and can be obtained from an autoparts store), a jar (to collect the old fluid), some beverages and munchies to keep your helpers happy and about an hour or two of free time. Note: Be careful of brake fluid as it is highly corrosive and will eat paint quite easily. Place a few rags under the fluid reservoir to catch any spillage when adding fluid.


Place the car on jack stands and remove all four wheels. On the back side of the brake caliper is a small nipple with a small rubber cap. Remove the rubber cap, and clean the nipple if any grease is present. Place the wrench over the nipple, then attach the bleed tube onto the nipple with the other end going into the jar. Make sure the tube is completely over the nipple. Now you are ready to start the process. You need to follow a basic command structure to make sure the process is done in the proper order. One person sits in the drivers seat, and the other works the wrench. If you have a third person, he can make sure the fluid level in the brake reservoir is constantly full (see photo). Otherwise, you'll have to stop periodically to make sure the brake fluid never goes below the "low" line.


The order you should do the brake bleeding is: left rear, right rear, right front, and left front. The bleeding procedure is as follows: Open the nipple about 1/3 of a turn counterclockwise, call out "Down" to the person sitting in the seat to push the brake pedal slowly down to the floor (about 1 to 2 seconds is slow enough). When the pedal is down to the floor, the person in the seat then calls out "Down", and HOLDS the pedal to the floor. When you hear "Down", close the nipple snugly so that no air can enter, then call out "Up" to the person sitting in the seat to let the pedal raise, the seated person then calling out "Up" when the pedal is fully released. Then start the procedure all over again.


The most important part of this procedure is to make sure that the pedal remains fully planted to the floor until the nipple is completely tightened. If not, then when the pedal is raised, air will be drawn into the brake line through the nipple and that is bad, as air is compressible, leading to poor brake pressure. If you do get air in the line, follow the above procedure until you are sure that the fluid being pushed out of the line is free of air bubbles.


Do about 5 cycles of the above procedure, then stop and check the fluid level. Add fluid to maintain the level as close to full as possible. When the fluid coming out the bleed tube looks as clear as the new fluid, then you have completely filled that brake line with new fluid. Be sure the nipple is tight and the little rubber cap is back on the nipple, then move onto the next brake line. Each brake line will take less time to drain old fluid than the previous because the previous bleed pulled new fluid through the junctions that interconnect the brake lines. When done, press the brake pedal a few times. It should be just as firm, or more firm than when you started. If not, then you got air in the line somewhere and need to start over.


If you have the time and inclination, you might also want to change the clutch fluid. The same new brake fluid is used, and the same procedure as well (except the seated person pushes the clutch pedal instead of the brake pedal). Look through the back of the right-front wheel well underneath the car. Towards the center line of the car, there is a small cylinder with a plunger coming out one end. This is the slave cylinder. On this cylinder is a nipple where the clutch fluid is to be drained. The clutch reservoir is to the right of the brake reservoir, and closer to the firewall. It is also smaller. Follow the above bleeding procedure, checking to make sure the fluid level never goes below "low" in the reservoir. When done, the clutch pedal should have a nice, constant pressure when depressed. When done, carefully test your car in your driveway to make sure the car stops when you press the brakes and the car will change gears when you press the clutch.


A little disclaimer is in order. Both the brake pad and brake fluid change are fairly simple, but done incorrectly can lead to smashed sheet metal and smashed bodies if you have no brakes. If you are uncomfortable about doing this procedure, then have an honest-to-deity mechanic do the job.


Disclaimer

Please note that these tips and pointers are not reviewed or approved by Mazda Motor Corporation or any other corporation or entity other than the originator. The San Diego Miata Club does not accept any liability for damage or injury as a result of utilizing these tips and pointers. Please use common sense and always remember safety first.


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