Brake fluid is poisonous. It also dissolves paint a lot. See the Warning at the beginning of the Section Bleeding the hydraulic brake system.
Description
On E28 models (in style «retro») hydraulic booster is used. Booster unit located between the brake pedal (for left hand drive models) or cross shaft lever (for right hand drive models) and master cylinder, actuated by fluid pressure produced by a power steering pump. With the engine running, the steering pump supplies pressure to the pressure regulator/accumulator. The regulator / accumulator accumulates and regulates the pressure in the vacuum hydraulic booster. When the brake pedal is depressed, the booster pressure helps actuate the master cylinder, reducing the required pedal force.
The vacuum hydraulic booster is not subject to major repairs; in case of failure, it should be replaced. Checking the operation of the system requires special tools, so even fault diagnosis is not within the competence of a home mechanic. If the system fails, take it to a dealer service department or other auto repair shop.
Removal and installation
1. With the engine off, discharge the hydraulic accumulator by depressing the brake pedal 20 or more times.
2. Remove the master cylinder (see Section Removal and installation of the main brake cylinder).
3. Clean the area around the inlet and return fittings, then disconnect them. Plug the pipes to prevent dirt from entering the system and leaking fluid.
Even a tiny bit of dirt can damage the amplifier, so be especially careful not to let dirt enter the system with the tubes disconnected.
4. Working inside the passenger compartment, remove the lower left trim panels above the brake pedal (for left hand drive models) or glove box and trim (for right hand drive models). On left-hand drive models, also disconnect the pedal return spring.
5. Take a fixing clip and disconnect a pusher from a brake pedal or the lever of a cross shaft.
6. Give four fixing nuts and remove the vacuum amplifier.
7. Installation repeats the removal procedure in reverse order. Tighten the nipple connections of the hydraulic lines to the required torque.
Do not attempt to tighten these connections without a wrench. If they are poorly tightened, they may leak, which will affect the operation of the system; overtightening them can damage the threads, which will also lead to leakage. To properly tighten these connections, you will need a special split socket for your wrench.
8. At the end of work, bleed the hydraulic brake system (Chapter Bleeding the hydraulic brake system) and adjust the brake pedal travel and brake light switch (see Section Brake pedal adjustment).