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

TSB Revision

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

TSB Revision

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

).