Intro: Bleeding Air From a Brake Line.
Changing out your brake fluid is good since the fluid absorbs moisture over time and this causes your brakes to be less responsive. Also bleeding removes trapped air no matter how small and allows you to inspect your braking system.
I recently got air ingress in one of my rear lines after a job I did on the rear hub. I needed to bleed out the line and remove that nasty air since my Brakes became useless as a result.
Bleeding brake lines is easy and can be done by one person. My method is common and uses little new brake fluid and is pretty fast.
Any container of brake fluid you use must be totally used or you can safely dispose of the remainder. Do not reuse left over brake fluid as this will absorb moisture over time and compromise your brake system!
When bleeding all four lines please consult your car's service manual to tell you which order of wheels to operate. Mines is RR, FL, RL then FR.
Step 1: Connect Tubing and Collection Container.
First step is to connect the tubing to the bleed nipple. My rear nipple uses an 8mm spanner to open or close. The other end of the tubing goes into the collection container with that end pointing down. This way when the old fluid drains out and you release the brake pedal, the tubing pulls back on fluid and not air!
You must start your engine since the brake master cylinder needs the vacuum pull of the engine to make the hydraulics work.
Take a piece of steel or wood and use it to wedge the brake pedal down as far as u can. Next open the bleed nipple but you don't have to open it all the way, just a crack will do. You will see fluid come out. You can leave the spanner on it.
(An alternate and faster way to bleed any brake line is to have a person assist you. Let them pump the brakes pedal several times then mash it down. You would simply open a previously closed bleeder valve to let air and fluid out then close it shut. You can repeat this process as many times as you wish for the same brake line).
Step 2: Pump the Brakes to Get the Air Out.
Now you gotta pump that brake pedal a few times while keeping an eye on the fluid reservoir in the engine bay. Pump about 4 times then wedge the brake pedal down. Goto the bleed nipple and close it. You will notice fluid and bubbles in the tubing. This is good. Top up the reservoir, open the bleed nipple and repeat pumping then wedge the brake pedal again. Close the nipple and you should be better with your breaks. Just mash the brake pedal and feel how much stiffer it is.
Step 3: Clean Up and Enjoy.
I used too much new brake fluid (to give the line a good flush) but in practice you won't use much even for all four brakes. Just dispose the old fluid safely and enjoy your car! All in all it should take about 10 minutes a wheel and you may not need to remove the tire.