Land Rover Discovery: Brake Master Cylinder and Fluid Reservoir

1. Brake fluid reservoir cap
2. Brake fluid level switch
3. Brake fluid reservoir
4. Secondary circuit inlet port
5. Primary circuit inlet port
6. Brake master cylinder
7. Secondary circuit outlet port
8. Primary circuit outlet port
9. Clutch circuit outlet port (manual transmission only)

The brake master cylinder is attached to the front of the brake booster, on the driver's side of the engine compartment. The brake master cylinder is a tandem design that supplies pressure to two independent (primary and secondary) hydraulic circuits. Each circuit is connected between the calipers of diagonally opposing front and rear wheels to provide a fail safe brake system.

A reservoir is mounted on top of the master cylinder and retains sufficient volume of hydraulic fluid to allow for normal system use, and to compensate for the replenishment of the system as the brake linings wear. The reservoir is internally divided to provide an independent supply of fluid to each brake circuit, and prevents a single fluid leak from disabling both primary and secondary brake circuits. If a failure occurs in one brake hydraulic circuit the remaining circuit will still operate effectively, although brake pedal travel and vehicle braking distances will increase.

On vehicles with manual transmission, the brake fluid reservoir also supplies hydraulic fluid for operation of the clutch assembly

Brake Fluid Level Switch

1. Contact carrier
2. Contact
3. Float

The reservoir incorporates a brake fluid level switch that is hardwired to the Central Junction Box (CJB). When the reservoir fluid falls to a predetermined low level, the switch contacts close and provide a signal feed back to the CJB. The CJB then sends a message on the High Speed (HS) Controller Area Network (CAN) Powertrain bus to the Instrument Cluster (IC), which illuminates the brake fluid warning indicator lamp.

Hydraulic Brake Actuation / Description and OperationHydraulic Control Unit (HCU)

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