1995 ISUZU TROOPER Workshop Manual

COMBINATION VALVE/P & B
(PROPORTIONING AND BYPASS) VALVE
The combination valve/P & B valve contains two
sections, each serving a different function.
The proportioning section
of the combination valve/
P & B valve proportions outlet pressure to the rear
brakes after a predetermined rear
input pressure has
been reached. This is done to prevent rear
wheel lock­
up on the vehicles with light rear wheel loads.
The valve has a By-pass feature which assures full
system pressure to the rear brakes in the event of a
front brake system malfunction, also full front pressure
is retained in the event
of rear brake malfunction.
HYDRAULIC BRAKES 5A 9
The combination valve has a pressure differential
warning switch which is designed to constantly
compare front and rear brake pressure
from the
master
cylinder and turn on the brake system warning
light on the instrument panel in the event of a front or
rear system malfunction. The valve and switch are so
designed that the switch
will latch in the "warning"
position once a malfunction has occurred. The only
way the light can be turned off is to repair the
malfunction and
apply a pedal force required to
develop line pressure. The combination valve/P & B
valve is not repairable and must be replaced as a
complete assembly.
P&B valve
(Antilock brake system model only)
Master cylinder (Primary)
Combination valve (Rear wheel antilock model only)
Pressure differential warning switch
Master
cylinder (Secondary)
..(> ..(> Master cylinder (Secondary) Master
cylinder
(Primary)
..(> ..(>
Front brake
Rear brake
Combination Valve
Electrical Circuit Test (RWAL
model
Fig. 5A-4
only)
1.
2.
3.
Disconnect the wmng connector at the
combination
valve (Fig. 5A-5).
• Connect a jumper wire from the harness to
ground.
Turn the ignition key to
"ON".
•
The warning light should come on.
• If the light will not come on, check the bulb. If
the bulb is good, refer to Chassis Electrical
(Sec.
8) for further diagnosis.
Turn the ignition off.
• Disconnect jumper wire and connect the
harness to the switch
terminal.
Combination Valve (RWAL model only)
Warning
Switch Test
1. Raise the vehicle.
• Support
with suitable safety stands.
2. Attach a hose to a rear brake bleeder screw.
• Immerse the opposite end of the hose into a
container
partially filled with clean brake fluid.
3.
4.
5.
6.
7.
¢ Front RH brake
Front LH brake
Rear brake
• Make sure the master cylinder reservoir is full.
Turn the ignition key to "ON".
• Open
the bleeder screw while a helper applies
moderate pressure to the brake pedal.
•
The warning light should come on.
• Close the bleeder screw before the helper
releases
the brake pedal.
Reapply the brake pedal with moderate to heavy
pressure.
• The light should go out.
Attach a hose
to a front brake bleeder screw.
• Immerse the opposite end of the hose into a
container
partially filled with clean brake fluid.
• Make sure the master cylinder reservoir is full.
Turn the ignition key to "ON".
• Open
the bleeder screw while a helper applies
moderate pressure to the brake pedal.
•
The warning light should come on.
• Close the bleeder screw before the helper
releases
the brake pedal.
Reapply
the brake pedal with moderate to heavy
pressure.
• The light should go out.

5A-1 0 HYDRAULIC BRAKES
8. Turn the ignition key off.
• If the warning light does not come on during
steps 3 and
6, but does light when a jumper is
connected to ground, the warning switch
portion
of the valve is faulty. Do not
disassemble any portion of the valve. It must
be replaced.
9. Remove the safety stands.
• Lower the vehicle.
• Check and fill the master cylinder to the proper
level.
VALVE REPLACEMENT
Removal steps 1. Hydraulic pipes
2. Warning switch
connector (Combination valve only)
3. Bolt
4. Combination valve/P&B valve
Installation
steps
To install, follow the removal steps in the reverse order.
Fig. 5A-5
1••1 REMOVAL
• The combination valve/P & 8 valve is not
repairable and must be replaced as a complete
assembly.
• Care must be taken to prevent brake fluid from
contacting any painted surface.
1. Hydraulic pipes
• Plug the pipes to prevent the loss of fluid or the
entrance
of dirt.
2. Warning switch connector (Combination valve
only)
3. Bolt
4. Combination valve/P & B valve
1••1 INSTALLATION
4.
3. Combination valve/P & B valve
Bolt
I~I_T_o_r_qu_e_N_·_m_(lb_·_in_) ___,_ ___ 1_3_(_1_13_) __ _
2. Warning switch connector (Combination valve
only)
1. Hydraulic pipes
~~~ Torque N·m (lb·ft) 16 (12)
After installing the brake pipes, bleed brakes as
described in this section.
•

INSPECTION OF BRAKE PAD LINING
(Fig. SA-6)
Inspect the brake linings any time the wheels are
removed (tire rotation, etc.). Check both ends
of the
outer pad by
looking at each end of the caliper. These
are the points at which the highest rate
of wear
normally occurs. At the same time, check the lining
thickness on the inner shoe to make sure that it was not
worn prematurely. Some inboard shoes and linings
have a thermal layer against the shoe, integrally
molded
with the lining. This extra layer should not be
confused with uneven inboard-outboard lining wear.
Look
down through the inspection hole in the top of the
caliper to view the inner shoe. Whenever the thickness
of any lining is worn to within 1 mm (0.039 in) of the
shoe,
all disc brake pad and lining assemblies should
be replaced at the same time.
The disc pads have a
wear indicator that makes a noise
when the pad wear to a degree where replacement is
required.
100
Limit 11.0 mm (0.039 in) I
Fig. 5A-6
INSPECTION OF BRAKE ROTORS
In manufacturing the brake rotor, tolerances of the
braking surfaces
for flatness, parallelism and lateral
runout are held very close. The maintenance of close
tolerance
on the shape of the braking surfaces is
necessary to prevent brake roughness.
In addition to these tolerances, the surface finish must
be held to a specified range. The control ofthe braking
surface finish is necessary to avoid
pulls and erratic
performance and to extend
lining life.
Light scoring of the rotor surfaces not exceeding
0.38mm (0.015 in) in depth, which may result from
normal use, is not detrimental to brake operation.
Thickness Variation Check (Fig. 5A-7)
1. Thickness variation can be checked by measuring
the thickness
of the rotor at four or more points
around the circumference
of the rotor. All
measurements must be made at 29 mm (1.14 in)
front/22 mm (0.87 in) rear from the edge of the
rotor.
HYDRAULIC BRAKES 5A-11
Fig. 5A-7
~~~ Front Disc Brake Rotor Thickness
Standard mm (in) 26.0 (1.024)
Limit mm(in) 24.6 (0.969)
~~~Rear Disc Brake Rotor Thickness
Standard mm (in) 18.0 (0.709)
Limit mm (in) 16.6 (0.654)
2. A rotor that varies by more than 0.010 mm
(0.0004 in) can cause pedal pulsation and/or front
end vibration during brake applications. A rotor
that does not meet these specifications should be
refinished
to specifications or replaced.
Lateral Runout Check (Fig. 5A-8)
1. Adjust the wheel bearing correctly.
• Refer to "Front Drive Axle" in Section 4C.
2. Install 2 wheel nuts to retain rotor.
3. Fasten a dial indicator to the suspension so that
the indicator stylus contacts the rotor about
29 mm (1.14 in)-front/22 mm (0.87 in)-rear from
the rotor edge.
4. Zero the dial indicator.
5. Move the rotor one complete revolution and
observe
total indicated runout.
Fig. 5A-8