L322 Range Rover Brakes: Master Cylinder Overview & Function
BRAKES
70-6
DESCRIPTION AND OPERATION
Foundation Brakes
General
The brake system is a dual circuit type with Electronic Brake Force distribution (EBD) through DSC/ABS control. The
system comprises:
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Vacuum booster
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Tandem master cylinder with two central valves for DSC operation
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Brake fluid reservoir with reed contact fluid level switch
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Vented front discs/Solid rear discs
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Single piston calipers
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ABS hydraulic unit with integrated control module
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Pre-charge pump for DSC operation.
Front Brakes
The front brakes each comprise a hub mounted, single piston calliper assembly and a vented disc. The inboard side
of the disc is protected by a mud-shield. When hydraulic pressure is supplied to the calliper, the piston extends and
forces the inner pad against the disc. The calliper body reacts and slides on the guide pins to bring the outer pad into
contact with the disc.
Rear Brakes
The rear brakes each comprise a hub mounted, single piston calliper assembly and a solid disc. The operation is the
same as for the front brakes.
Both the left front inboard and right rear inboard brake pad wear is monitored by a sensor attached to the pad by a fly
lead. If the brake pad warning has been triggered the sensor and brake pads must be replaced.
Master Cylinder
The master cylinder assembly produces hydraulic pressure to operate the brakes when the brake pedal is pressed.
The assembly is attached to the front of the brake servo assembly, and comprises a cylinder containing two pistons
in tandem. The rear piston produces pressure for the primary circuit and the front piston produces pressure for the
secondary circuit.
The brake fluid reservoir is located on top of the master cylinder assembly. The reservoir is internally divided to
provide an independent supply of fluid to each brake circuit, and so prevent a single fluid leak from disabling both
primary and secondary brake circuits. Should a failure occur in one circuit, the remaining circuit will still operate
effectively, although brake pedal travel and vehicle braking distances will increase.
If the fluid level in the reservoir is too low, the brake fluid level switch in the reservoir filler cap breaks a contact to the
DSC ECU, which sends a CAN message to illuminate the brake warning lamp in the instrument pack and displays the
message 'CHECK BRAKE FLUID' in the instrument pack.
Brake Disc
344mm diameter -30 mm thick
Calliper
Single piston 60mm diameter
Pads
asbestos free
Brake Disc
354mm diameter -12mm thick
Calliper
single piston 42mm diameter
Pads
asbestos free