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How to Change Your Brake Fluid

The following is a guide to changing your brake fluid, it should be done quite often at the intervals specified in the cars service manual. This is because most brake fluids (none synthetic) are hydroscopic, that is they absorb water and water in the brake lines in not good and will lead to spongy brakes.

  • Never reuse any brake fluid. No matter how long its been sitting in a bottle. Its dirty whether you can see dirt or not and loaded with tiny bubbles that will not dissipate. Use good quality fluid too.
  • Always use the correct brake spanners to prevent rounding the bleeder. These have 5 corners rather than 3 and can still get it over the hose.

Brake nipple

  • When the car is jacked up use axle stands incase the jack gives way.
  • Cover the paintwork with towels and/or plastic bags. Brake fluid does is a better paint stripper than paint stripper itself.
  • Wrap the master cylinder with a rag so if you spill or overfill it will not cause damage.
  • Pour in new fluid slowly. Don't let it go gulp for example. When done, replace the bottle cap so if you knock it over it won't cause a disaster
  • Before you start check the condition of the braking system and any hoses which appear/feel soft, or have cuts or rubber chunks missing must be replaced. Using metal braided hoses will also help you get firmer pedal.
  • If you are uncertain about any of the system replace it your life will depend upon it.
  • Always start bleeding at the farthest wheel and work your way back on the same circuit.
  • Use a clear 1 foot hose on the bleeder and the other end in a clear jar with some clean fluid (keep that end under fluid level).
  • Never let the master cylinder reservoir run too low. Don't let it get past half way down as it will start to suck air and then you are back to square one.
  • When bleeding a wheel this way you will need to have an assistant. Your assistant sits in driver seat and shouts the position of the pedal when its changed. You open the bleed nipple just a 1/4 turn or so and shout "DOWN" and assistant pushes GENTLY until it hits bottom, then holds it down and shouts "Down" to confirm position. You then close the bleed nipple and yell "UP". Assistant then returns pedal to upper position and shouts "UP" to confirm position. If you each don't shoutl your position you'll end up opening the bleeder at its worst moment and you will have to go through the procedure again. Repeat this process a few times. Then check the masters reservoir level and refill if needed. Continue on that bleed nipple until you see clean air free fluid coming down the clear hose into the bottle.
  • Follow your manuals bleeding sequence for the next wheel - usually other back wheel.
  • Keep going around the car and make sure you never run low on the reservoir or you'll have to start the process all over.

If you do not have an assistant or you don't want to do it the old fashoned way the way I do it is to use a Gunson Eezi bleed.

This is a great system as it uses air pressure (from a spare wheel) to pressurize the system so all you have to do is to go to each wheel and turn the bleed nipple, the old fluid will come out and because the system is under pressure then there is no way air can enter the system. Once the clean fluid is coming through the nipple can be closed off and thats one wheel done. The system will not run out of brake fluid as the system has its own reservoir which you fill up at the start. It is much easier than the old method and has the advantage that you can do it by yourself. The last time I did the brakes on the MGB I could not get them right until I used the Gunson Eezi bleed, now I would not be without one.