Frelander 2. Manual - part 118

Stoplamp switch

Hydraulic pipes

Integrated Hydraulic Control Unit (HCU) and Anti-lock Brake System (ABS) module

Brake master cylinder and fluid reservoir

OVERVIEW

The hydraulic brake system is a diagonally split dual circuit system and consists of the brake pedal, brake master cylinder,
HCU and the hydraulic pipes and hoses. The system also features a non-active brake booster.
For additional information, refer to: Brake Booster (206-07 Power Brake Actuation, Description and Operation).

The preformed rigid brake pipes distribute pressure from the master cylinder to the 4 brake calipers, via the integrated
HCU and ABS module. Flexible hoses connect the rigid brake pipes to the front and rear calipers.

BRAKE PEDAL

Item

Part Number

Description

Stoplamp switch

The brake pedal is mounted in a bracket that is attached to the rear side of the engine bulkhead. The pedal assembly is
different for LHD and RHD vehicles, and is connected to the brake booster push rod with a clevis pin.

The stoplamp switch is mounted on the brake pedal bracket and will illuminate the vehicle stoplamps when the brake
pedal is pressed. The stoplamp switch is also used as an input to the speed control system, and will cancel the current
speed setting when the brake pedal is pressed. For additional information, refer to:

Speed Control - 3.2L (310-03 Speed Control - 3.2L, Description and Operation),
Speed Control - 2.2L Diesel (310-03 Speed Control - 2.2L Diesel, Description and Operation).

BRAKE MASTER CYLINDER AND FLUID RESERVOIR

Item

Part Number

Description

Brake fluid reservoir cap

Brake fluid level switch

Brake fluid reservoir

Secondary circuit inlet port

Primary circuit inlet port

Brake master cylinder

Screw

Primary circuit outlet port

Secondary circuit outlet port

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 2 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

Item

Part Number

Description

Contact carrier

Contact

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
broadcasts a message on the medium speed Controller Area Network (CAN) bus to the instrument cluster that in turn
illuminates the brake fluid warning indicator lamp.
For additional information, refer to: Instrument Cluster (413-01 Instrument Cluster, Description and Operation).

HYDRAULIC CONTROL UNIT

Item

Part Number

Description

Brake pipe to LH front caliper

ABS module

Brake pipe to RH front caliper

Master cylinder primary circuit connection

Brake pipe to LH rear caliper

HCU

Brake pipe to RH rear caliper

Master cylinder secondary circuit connection

The HCU is located on the rear LH side of the engine compartment and is an integral component with the ABS module. The
HCU is a 4 channel unit that modulates the supply of hydraulic pressure to the brakes under the control of the ABS
module.

The primary and secondary outlet ports of the master cylinder are connected via 8 mm (0.315 in) diameter brake pipes to
the primary and secondary circuits of the HCU. The primary circuit in the HCU provides 2 separate outlet ports to the RH
front and LH rear brakes. The secondary circuit in the HCU provides 2 separate outlet ports to the LH front and RH rear
brakes.

The HCU incorporates 3 brake operating modes as follows:

Normal braking/ Electronic Brake Force Distribution (EBD)
ABS braking
Active braking.

As the HCU and ABS module is a fully integrated unit, the description and operation details for the HCU and ABS
functionality, including the 3 braking modes, are detailed in the Anti-Lock Control - Stability Assist section of the manual.
For additional information, refer to: Anti-Lock Control - Stability Assist (206-09 Anti-Lock Control - Stability Assist,
Description and Operation).

Servicing Information

The ABS module and HCU form a single component and must not be separated. The ABS module and HCU assembly is
supplied in a pre-filled state. After installation, the hydraulic brake system only requires a conventional bleed of the
system; there is no requirement to pressure bleed the system.

• NOTE: The ABS module and HCU is a fragile component and must be discarded if dropped or damaged.

PRINCIPLES OF OPERATION

As the brake pedal is pressed, the front push rod in the brake booster pushes the master cylinder primary piston along the
bore of the housing. This produces pressure in the primary pressure chamber and in conjunction with the primary spring,
overcomes the secondary spring and simultaneously moves the secondary piston along the bore.

The initial movement of the pistons away from the piston stops closes the primary and secondary center valves located
inside the master cylinder. Further movement of the pistons then pressurizes the fluid in the primary and secondary
chambers and the brake circuits. The fluid in the chambers behind the pistons is unaffected by the movement of the

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