Page 592 of 873

BRAKES
1
DESCRIPTION AND OPERATION BRAKES
Discovery vehicles have servo assisted brake
systems and the option of an anti-lock brake system.
Information in this section refers to components
relevant to both brake systems. Where the system
components are different they are referred to as ABS
or NON ABS
BRAKE SYSTEM NON ABS
Description
The servo assisted hydraulic braking system is the
dual line type, incorporating primary and secondary
hydraulic circuits.
NOTE: References made to primary or
secondary do not imply main service
brakes or emergency brakes but denote
hydraulic line identification.
The brake pedal is connected to a vacuum assisted
mechanical servo which in turn operates a tandem
master cylinder. The front disc brake calipers each
house four pistons, these pistons are fed by the
secondary hydraulic circuit. The rear disc brake
calipers each house two pistons, these are fed by the
primary hydraulic circuit via a pressure reducing valve.
A brake fluid level switch is incorporated into the
reservoir cap assembly, the switch will immediately
illuminate a warning light in the instrument binnacle
indicating low fluid or sudden fluid loss.
The brake fluid reservoir is divided, the section closest
to the servo feeds the primary circuit and the section
furthest from the servo feeds the secondary circuit.
Under normal operating conditions both the primary
and secondary circuits operate simultaneously on
brake pedal application. In the event of a failure in the
primary circuit the secondary circuit will still function. If
the secondary circuit fails the primary circuit will still
function. The brake pedal travel will be longer in the
event of a half system failure.If the servo should fail, both hydraulic circuits will still
function but would require greater pedal effort due to
the lack of vacuum assistance. The hand operated
parking brake acts on a brake drum at the rear of the
transfer gearbox and is completely independent of the
hydraulic circuits.
Hydraulic circuit non ABS
Key
A = Primary hydraulic circuit
B = Secondary hydraulic circuit
C = Pressure reducing valve
Page 593 of 873
70BRAKES
2
DESCRIPTION AND OPERATION ABS COMPONENTS
Location
Key to diagram
1. ABS Modulator unit
2. Servo/Master cylinder
3. Pressure reducing valve
4. Electronic control unit5. Rear sensors/exciter rings
6. Front sensors/exciter rings
7. Diagnostic plug connection
Page 595 of 873

70BRAKES
4
DESCRIPTION AND OPERATION System description
The brake system consists of dual hydraulic circuits in
a front - rear split. That is individual circuits to front
and rear axles.
Wheelspeed signals are provided by the fitting of
exciter rings to axles and speed sensors.
An ABS stop light switch is fitted to provide a braking
signal to the ECU as well as operate the stop lights.
Electrical wiring is provided as necessary with system
relays and fuses. Discovery Electrical Troubleshooting
Manual gives the location and wiring circuits of these
components.
Visual warning of system malfunction is provided via a
warning light in the instrument panel.
Hydraulic circuit ABS
Key
A = Primary hydraulic circuit
B = Secondary hydraulic circuit
C = Pressure reducing valve
D = ABS ModulatorABS System operation
During normal braking the feel of the brake pedal on
vehicles equipped with ABS will be the same as that
on non ABS vehicles. During ABS cycling the driver
will experience feedback in the form of a pulsating
brake pedal and solenoid/pump motor noise from the
Modulator.
The system is fully automatic in operation both on and
off road, and will only act when the ECU detects that
ABS cycling is necessary. The ECU continually
monitors the operation of the system.
When starting the ABS system will go through a series
of self checks, including a check of the solenoid
valves/pump motor.
WARNING LIGHT
The warning light will be on during the self check
(1.3-2 secs). If no faults are stored in the memory the
light goes out for 0.5sec,then comes on again. It will
then remain on until the vehicle is driven faster than 7
kph/5mph. This is the only time that the light will be on
without indicating a problem.
Any faults detected by the ECU will cause the warning
light to illuminate indicating that the vehicle may not
have full ABS control.
Page 596 of 873
BRAKES
5
DESCRIPTION AND OPERATION BRAKE PIPE LAYOUT ABS
Left hand drive shown. On right hand drive vehicles the master cylinder and servo unit only move
position.
KEY
1. Connector double elbow
2. Rear left brake
3. Modulator to rear left brake
4. Modulator to master cylinder
5. Modulator to pressure reducing valve upper
6. Electrical connection
7. Modulator unit
8. Nut, mounting bush and cup
9. Modulator to front left brake
10. Front left brake
11. Electrical connection12. Modulator to front right brake
13. Modulator to pressure reducing valve lower
14. Master cylinder to pressure reducing valve lower
15. Front right brake
16. Bolt
17. Pressure reducing valve
18. Modulator to pressure reducing valve upper
19. Master cylinder
20. Servo unit
21. Modulator to rear right brake
22. Rear right brake
Page 597 of 873
70BRAKES
6
DESCRIPTION AND OPERATION BRAKE PIPE LAYOUT NON ABS
Left hand drive shown. On right hand drive vehicles the master cylinder and servo unit only move
position.
KEY
1. T-Connector
2. Rear left brake
3. Master cylinder to pressure reducing valve lower
4. Front left brake to pressure reducing valve upper
5. Front left brake
6. Front right brake
7. Master cylinder to pressure reducing valve lower8. Pressure reducing valve
9. Front right brake to pressure reducing valve
upper
10. Master cylinder
11. Servo unit
12. Pressure reducing valve upper to both rear
brakes
13. Rear right brake
Page 610 of 873
70BRAKES
8
REPAIR MASTER CYLINDER ASSEMBLY NON ABS
Key to master cylinder
1. Water ingress seal
2. Transfer housing
3. Vacuum seal
4. Guide ring
5. Retaining ring
6. 'O' ring seal7. Primary plunger assembly
8. 'L' seal
9. Secondary plunger
10. Washer
11. Recuperating seal (primary
cup)
12. Seal retainer13. Springs (2 off)
14. Swirl tube
15. Master cylinder body
16. Reservoir seals
17. Reservoir
18. Low fluid level switch and
cap
NOTE: Thoroughly check that no debris is lodged in fluid passageways and drillings. If debris is
found, carefully remove, re-clean cylinder and re-check.
Page 614 of 873
70BRAKES
12
REPAIR FRONT BRAKE CALIPER ASSEMBLY
Key to caliper
1. Caliper
2. Bleedscrew
3. Antirattle springs
4. Pad retaining pins
5. Split [cotter] pin
6. Friction pads
7. Piston
8. Wiper seal retainer
9. Wiper seal
10. Fluid seal
11. Brake disc
Page 619 of 873
BRAKES
17
REPAIR REAR BRAKE CALIPER ASSEMBLY
LH Rear Caliper illustrated
Key to caliper
1. Caliper
2. Bleed screw
3. Pad retaining springs
4. Brake pads
5. Piston6. Wiper seal retainer
7. Wiper seal
8. Fluid seal
9. Retaining pins