Mitsubishi Montero (2002-2004). Manual — part 995

GENERAL DESCRIPTION

TSB Revision

BASIC BRAKE SYSTEM

35A-5

HYDRAULIC BRAKE BOOSTER (HBB)
OPERATION

1. When the pedal operating force is transmitted in

turn by the operating rod, the power piston and
the master cylinder piston, the regulator piston
and the spool valve move to the left.

2. When the spool valve opens line A and closes line

B, the accumulator pressure is supplied to the
rear brakes. This pressure is introduced to the
booster chamber and provides power assistance
to move the master cylinder piston to the left.

3. Then, when the pressure in the booster chamber

increases, the pressure which is applied to the
rear (left side) of the reaction disc also increases,
and the reaction disc starts to change shape. The
reaction disc contacts the reaction rod, and the
reaction rod in turn contacts the spool valve, so
that the master cylinder pressure being applied
towards the left and the booster pressure being
applied to the right are brought into balance by the
reaction disc. This allows the power-assist
hydraulic pressure generated by the pedal
operating force to be kept at an equilibrium.

.

<When booster is not operating>

.

<When booster is operating>

.

AC000676

AC000676 AB

ACCUMULATOR

RESERVOIR

CHECK
VALVE

PUMP
MOTOR

PRESSURE
SWITCH

LINE B (OPEN)

LINE A (CLOSED)

RETURN SPRING

REACTION DISC

REACTION ROD

SPOOL
VALVE

REAR

FRONT

REGULATOR PISTON

MASTER CYLINDER RETURN SPRING

MASTER CYLINDER PISTON

POWER PISTON

BOOSTER CHAMBER

OPERATING ROD

MASTER CYLINDER
MECHANISM

AC000677AB

ACCUMULATOR
PRESSURE

LINE B
(CLOSED)

LINE A
(OPEN)

SPOOL
VALVE

ASSIST
FORCE

BOOSTER
CHAMBER

OPERATING ROD

REACTION ROD

REACTION
DISC

REAR

FRONT

POWER PISTON

BASIC BRAKE SYSTEM DIAGNOSIS

TSB Revision

BASIC BRAKE SYSTEM

35A-6

<When a loss of accumulator pressure occurs>
If a loss of accumulator pressure occurs because of
a problem such as a pump motor problem, the power
assist force and rear brake pressure cannot increase
in response to the input from the brake pedal.
Accordingly, the front brakes can be operated
directly by depressing the brake pedal, but the rear
brakes do not operate at all.

BASIC BRAKE SYSTEM DIAGNOSIS

INTRODUCTION

M1351009700223

The hydraulic brake system consists of the brake
pedal, the hydraulic brake booster (HBB), and the
disc brakes. Insufficient braking power or noise may
occur due to wear, damage or incorrect adjustment
of these parts.

DIAGNOSTIC TROUBLESHOOTING STRATEGY

M1351009800220

Use these steps to plan your diagnostic strategy. If
you follow them carefully, you will be sure that you
have exhausted most of the possible ways to find a
basic brake system fault.
1. Gather information from the customer.

2. Verify that the condition described by the

customer exists.

3. Find the malfunction by following the symptom

chart.

4. Verify malfunction is eliminated.

SYMPTOM CHART

M1351009900238

SYMPTOM

INSPECTION
PROCEDURE

REFERENCE
PAGE

Vehicle pulls to one side when brakes are applied

1

P.35A-7

Insufficient braking power

2

P.35A-8

Increased pedal stroke (Reduced pedal-to-floor board clearance) 3

P.35A-9

Brake drag

4

P.35A-9

Scraping or grinding noise when brake are applied

5

P.35A-10

Squealing, groaning or chattering noise when brake are applied

6

P.35A-11

Squealing noise when brakes are not applied

7

P.35A-11

Groaning, clicking or rattling noise when brakes are not applied

8

P.35A-12

BASIC BRAKE SYSTEM DIAGNOSIS

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BASIC BRAKE SYSTEM

35A-7

SYMPTOM PROCEDURES

INSPECTION PROCEDURE 1: Vehicle Pulls to One Side when Brakes are Applied

DIAGNOSIS

STEP 1. Check for oil, water, etc., on the pad
contact surface of all brakes.

Q: Is oil, water, etc., on the pad contact surface?

YES :

Replace the pads on both left and right

wheels as a set and determine the source/
cause of foreign material. Then go to Step 5.

NO :

Go to Step 2.

STEP 2. Check disc brake pistons for smooth
operation.
(1) Depress the brake pedal repeatedly more than

40 times with the ignition switch at the "LOCK"
(OFF) position to release the pressure in the HBB
power supply system.

(2) Test each disc brake assembly one at a time.

a. Remove the lower caliper bolt, then remove

caliper from mount.

b. Have an assistant slowly depress the brake

pedal. Confirm piston(s) extend slowly and
smoothly with no jumpiness. Repeat for each
disc brake assembly.

Q: Do (does) the piston(s) move correctly?

YES :

Go to Step 3.

NO :

Disassemble and inspect brake assembly
(Front: Refer to

P.35A-142

/Rear: Refer to

P.35A-148

). Then go to Step 5.

STEP 3. Check brake disc(s) for run-out.
Refer to

P.35A-130

.

Q: Is run-out outside of specifications?

YES :

Repair or replace as necessary. Then go to

Step 5.

NO :

Go to Step 4.

STEP 4. Check brake discs for correct thickness.
Refer to

P.35A-130

.

Q: Is the thickness outside of specifications?

YES :

Repair or replace as necessary. Then go to

Step 5.

NO :

Go to Step 5.

STEP 5. Retest the system.

Q: Is the symptom eliminated?

YES :

The procedure is complete.

NO :

Start over at Step 1. If a new symptom
appears, refer to the appropriate symptom
chart (

P.35A-6

).

BASIC BRAKE SYSTEM DIAGNOSIS

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BASIC BRAKE SYSTEM

35A-8

INSPECTION PROCEDURE 2: Insufficient Braking Power

DIAGNOSIS

STEP 1. Check whether the brake fluid is low, is
the correct fluid (transmission fluid, engine oil,
etc.), or is contaminated (debris, sand, etc.).

Q: Is there fault?

YES :

Refill or replace with the specified brake

fluid DOT 3 or DOT 4. Bleed the brakes if
necessary (Refer to

P.35A-122

). Then go to

Step 6.

NO :

Go to Step 2.

STEP 2. Check for spongy (not firm brakes).
(1) Depress the brake pedal repeatedly more than

40 times with the ignition switch at the "LOCK"
(OFF) position to release the pressure in the HBB
power supply system.

(2) With the brake pedal fully released, depress the

brake pedal slowly until it stops.

(3) With a measuring stick (ruler, etc.) next to the

brake pedal, depress the pedal firmly and
measure the distance the pedal traveled.

Q: Is the distance greater than 20 mm (0.8 inch)?

YES :

Bleed the brakes to remove air in the fluid

(Refer to

P.35A-122

). Then go to Step 6.

NO :

Go to Step 3.

STEP 3. Check the HBB function.
Refer to

P.35A-117

.

Q: Is the HBB malfunctioning?

YES :

Check the HBB (Refer to

P.35A-136

) and

replace the faulty part as necessary. Then
go to Step 6.

NO :

Go to Step 4.

STEP 4. Check for pinched or restricted brake
tube or hose.

Q: Is there a pinched or restricted brake tube or hose?

YES :

Replace that complete section of brake tube

or brake hose. Then go to Step 6.

NO :

Go to Step 5.

STEP 5. Check for oil, water, etc., on the pad
contact surfaces of all brakes.

Q: Is oil, water, etc., on the pad contact surface?

YES :

Replace the pads on both left and right

wheels as a set and determine the source/
cause of foreign material. Then go to Step 6.

NO :

Go to Step 6.

STEP 6. Retest the system.

Q: Is the symptom eliminated?

YES :

The procedure is complete.

NO :

Start over at Step 1. If a new symptom
appears, refer to the appropriate symptom
chart (

P.35A-6

).