Brake fluid needs to be changed (flushed) for three reasons: Maintenance - changing old brake fluid removes water from the brake system. Brake fluid is hydroscopic, it absorbs water. Old brake fluid must be flushed out or water absorbed by the fluid eventually causes internal rust on the disk calipers and pistons.
Performance - changing old brake fluid helps high temperature operation because fresh (dry) brake fluid has a higher boiling
point than older (wet) brake fluid. If brake fluid boils, compressible gas bubbles form, resulting in a very spongy brake pedal.
Repair - flushing your brake fluid can fix some problems you may be having, such as a mushy brake pedal, or if the pedal goes
down far and you can pump it quickly and make the pedal firm again.
Also, see this article from AAA regarding the importance of flushing your brake fluid.
Procedures
1-2 hours
Tools required:
hydraulic jack
jack stands
flat screwdriver
wrench for bleeder on calipers/drum cylinders, usually 9 to 13mm
newspaper to catch spills under each wheel
a length of aquarium air hose or similar
an extra container to catch old brake fluid
paper towel
a willing assistant (wife/friend, etc)
2 bottles of DOT3 brake fluid (consult your owner's manual for correct type)
turkey baster or syphon
Procedure:
Place the vehicle on jack stands on a flat surface. If you don't have enough stands you can do one wheel at a time. Remove
the wheels.
Syphon off the old brake fluid in the master cylinder reservoir under the hood.
Fill the reservoir with new brake fluid (don't reuse old fluid as it holds moisture and will corrode your brake system).
Start with the brake farthest from the master cylinder, usually rear wheel, passenger side. Pull off the rubber cover on the
bleeder valve. Attach the aquarium air line to the nipple on the bleeder.
Have your assistant pump the brake pedal up and down 3-4 times, then hold the pedal down fairly hard.
Open the bleeder, let fluid flow out through the air line into a waste container. (preferrably a clear bottle so you can see
any air bubbles escaping the system). When the fluid stops and your assistant's foot hits the firewall (brake pedal all the
way down), close the bleeder valve immediately!
Go to step #5 above and drain more fluid out of the bleeder valve until clean fluid comes out. Check the master cylinder
everytime and top it up as necessary. This procedure uses lots of fluid.
Now move to the rear brake on the driver's side. Go to step #5 and repeat the same procedures above until clean fluid comes
out of the bleeder valve and no bubbles.
Next is the front brake, passenger side, same procedure.
Last is the driver's side front brake, same procedure.
When finished check for any leaks, remount rubber covers on the bleeder valve nipples. Remount all wheels, re-torque lug nuts
after 50-100 miles of driving.
Start vehicle and depress the brake pedal. It should feel much less spongy than before this procedure. If not, there is air
in the system, start over. Bleed everything again.
Note: if you assistant releases the brake pedal before you can close the bleeder valve then air will be introduced into the
brake lines. This is no good! Before you start tell your assistant you will tell him/her PUMP, HOLD DOWN, RELEASE commands. That's it, you're done. Congratulate yourself on saving some cash instead of handing it over to a mechanic.
You can also do this procedure by yourself using a hand operated "power" bleeder. Basically this is a hand-pump device with a brake fluid reservoir. You siphon off as much oil as you can from the master cylinder, then connect this device with a hose to the wheel cylinder/brake caliper bleeder nipple, open the nipple and pump the unit to force fresh brake fluid up to the master cylinder. Repeat for each wheel and occasionally drain the master cylinder of old oil.
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