Originally Posted by F22-GURU

This is a guide for those who are not familiar with the correct procedures of Replacing a Brake Master Cylinder.(BMC)

If you have to Replace the BMC make sure you Bench Bleed it Before installing to the vehicle. Before you remove the old BMC, mark the brake lines to correspond to the ports.
You can Bench Bleed a BMC by clamping it in a Vice. Fill up the BMC with approved DOT 4 BF. Remove the Rubber Blanking plugs, Lay down a couple of large rags to catch the brake fluid.
Step 1. Using a No 3 Phillips Head Screwdriver (or equivalent tool),push the piston in fully and hold.
Step 2. Cover All Ports with your Thumbs or fingers (Having a helper will be much easier).
Step 3. Now release the piston only when the ports are covered.
Step 4. Push the piston back in fully (slowly).
Step 5. Repeat Steps 1 - 4 Until there is no more air in the BMC.
Step 6. Refit the Blacking Plugs so you don't lose BF from the BMC.
Step 7. Fit the New BMC onto the Vacuum Booster.
Step 8. Refit & tighten the Brake Line to correct ports (Marked before removal)
Step 9. Have a friend sit in the drivers seat to operate the Brake Pedal.
Step 10. With Rags under the BMC to protect Paintwork etc, get your friend to lightly pump the brake pedal SLOWLY.
Step 11. Using the correct size Flare Pipe Spanner, Crack open the ports, only one at a time. Start with the rear pipe.
Step 12. Ask your friend to push the Brake Pedal Down Slowly until it reaches the floor (Be Careful not to push the pedal too fast as it may pop the seals inside the Brake Booster).
Step 13. Tighten the Port Up.
Step 14. Top up the BMC Reservoir and Repeat Steps 11 - 14 with all other ports including bleeding at the Calipers.
Step 15. Once all the air is bled out of the brakes. Wash off all excess BF with good old H2O. (Which neutralises the BF)

If there is any questions just PM me and I'll do my best to answer your queries.

Cheers
Geoff Cubbon
GEN46L