Genuine BMW Z4 Brake Master Cylinder

BMW Z4 Brake Master Cylinder Parts Questions & Experts Answers

• Brake Master Cylinder
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  Q:

  What precautions and steps should be followed before replacing the Brake Master Cylinder on the BMW Z4?

  Posted by Brooke E.

  A:

  As a first step, always adhere to the requirements and the whistle blow before commencing work. With the use of a new brake master cylinder, brake master cylinder retaining nuts will be needed when assembling the vehicle. Should the brake master cylinder be worn out, then it cannot be repaired normally, as BMW considers them to be sealed and their repair kits could not be sourced from the dealers. It is mandatory to change the brake master cylinder O-ring seal and the reservoir seals irrespective of their condition. On models fitted with ABS, while it is sometimes possible to remove the brake master cylinder, loosening the hydraulic fittings will cause air to enter the high-pressure hydraulic system, which can only be safely bled using the BMW dealer or specialist versions of the service tester. Consequently, after installation, the vehicle should be moved to a certified dealer. First, one has to remove the heater/ventilation inlet air ducting if the brake master cylinder is to be removed. The brake pedal should be pushed while the key is in the starting position to empty the brake hydraulic reservoir, the best practice being the use of a syringe or vacuum pump and never use mouth to suck the fluid because of its toxicity. Removing the wiring connector from the brake fluid reservoir and the fluid hose or hoses and fitting the ends to avoid dripping of the fluid. Unscrew the brake master cylinder reservoir retaining screw and gently take out the fluid reservoir while noting to save the seals and also plugging on the cylinder ports. It is necessary to clean the surrounds of the brake line fittings indicating their position before undoing the fitting nuts and pulling the lines and then cover the ends with the plugs or tape to avoid the entry of dirt and to protect it from leaking when taking the vehicle for a test drive. Unbolt the two nuts and washers which hold the brake master cylinder to the power Brake Booster and discard them along with the retaining nuts and prepare a new set of nuts and washers to be fitted. The mating surfaces should then be cleaned with clean rags, a new O-ring inserted and the brake master cylinder slid into position and oriented correctly with regards to the booster pushrod. Tighten the new retaining nuts with adequate force and secure the brake line fittings and reservoir seals then connect the fluid hoses and electrical connections. Last but not least of course is to take the brake master cylinder reservoir and fill it with a new kind of fluid and to bleed the hydraulic system.

  Answered by BMW Parts Specialist Adrian / Jun 28, 2026