Checking brake booster

AR43.10-P-0325RT

Checking brake booster

10.11.11



Checking

 Danger!

Risk of poisoning caused by swallowing brake fluid. Risk of injury caused by brake fluid coming into contact with skin and eyes.

Only pour brake fluid into suitable and appropriately marked containers. Wear protective clothing and eye protection when handling brake fluid.

AS42.50-Z-0001-01A

 Danger!

Risk of death caused by vehicle slipping or toppling off of the lifting platform.

Align vehicle between columns of vehicle lift and position four support plates at vehicle lift support points specified by vehicle manufacturer.

AS00.00-Z-0010-01A



Brake fluid notes

AH42.50-P-0001-01A



Notes on repairs to brake system

AH42.00-P-0003-01A

1

Open engine hood and raise to vertical position

AR88.40-P-1000RT

2

Connect vacuum tester (1) to brake booster (3).

 Observe manufacturer's operating instructions in order to prevent erroneous measurement or faulty operation.

AR43.10-P-0024-01RT

 Reduce vacuum of brake pedal beforehand by pressing pedal several times.

 Test connection

*168589086300

 Vacuum tester

*201589132100

3

Connect brake fluid changing equipment

 Pay attention to manufacturer's operating instructions.

Brake fluid change unit

gotis://B_42/43.2_01

4

Raise vehicle using two-post lift

 Only lift vehicle until wheels have sufficient ground clearance.

AR00.60-P-1000RT

Two-post lifting platform 3.0-3.5 t, electromechanical
gotis://H_00.1_01.0

5

Take off left front wheel



Remove/install wheels, rotate if necessary

AP40.10-P-4050RT

6

Remove bleed screw from floating brake caliper (7) and connect pressure tester (6).

 Pressure testers for hydraulic oil systems must not be used for systems with brake fluid otherwise brake fluid is mixed with mineral oil which can cause the brakes to fail.

 Observe manufacturer's operating instructions in order to prevent erroneous measurement or faulty operation.

 Collect escaping brake fluid.

Pressure tester

7

Bleed pressure tester (6) with brake fluid replacement unit

 Observe manufacturer's operating instructions in order to prevent erroneous measurement or faulty operation.

Brake fluid change unit

gotis://B_42/43.2_01

Pressure tester

8

Switch off brake fluid changing unit and release pressure

Brake fluid change unit

gotis://B_42/43.2_01

9

Install pedal force meter

 Observe manufacturer's operating instructions in order to prevent erroneous measurement or faulty operation.

 Install pedal force meter sensor (4) at brake pedal and set up pedal force meter display unit (5) so that it can be seen.

Pedal force meter
gotis://B_42/43.1_03.0

 Danger!

Risk of accident caused by vehicle starting off by itself when engine is running. Risk of injury caused by contusions and burns during starting procedure or when working near the engine as it is running

Secure vehicle to prevent it from moving by itself.
Wear closed and snug-fitting work clothes.
Do not touch hot or rotating parts.

AS00.00-Z-0005-01A

10

Start engine and create a vacuum of 0.75 to 0.8 bar by accelerating and then suddenly releasing the accelerator pedal.

 If a significantly lower vacuum is reached or if the vacuum drops again immediately, the O-ring between the brake booster (3) and tandem master brake cylinder may be damaged or the vacuum line with check valve (2) may be defective: 

Checking check valve

AR43.10-P-0023RT

Remove/install stepped tandem brake master cylinder, install new O-ring.

AR42.10-P-0310RT

11

Apply five specified brake pedal forces to brake pedal in succession

 Read off and note the relevant measured values of the brake line pressure on the low pressure gauge or on the high pressure gauge of the pressure tester (6).

 Measured values must be within specified ranges. With each measurement, ensure that a vacuum of 0.75 to 0.8 bar is maintained.

Brake pipe line pressure

*BE43.10-P-1002-01E

 Test connection

*168589086300

 Vacuum tester

*201589132100

Pedal force meter
gotis://B_42/43.1_03.0

Pressure tester

12

Turn off engine

13

Remove pedal force meter

Pedal force meter
gotis://B_42/43.1_03.0

14

Detach the pressure tester (6) and screw the bleed screw into the floating brake caliper (7) again

 Collect escaping brake fluid.

Pressure tester

15

Bleed brake system

 After the test only bleed the floating brake caliper (7) to which the pressure tester (6) was connected.

AR42.10-P-0010RT

 Pay attention to manufacturer's operating instructions.

Front axle:

Bleed screw to brake caliper

*BA42.10-P-1001-10L

Rear axle

Bleed screw to brake caliper

*BA42.10-P-1001-12L

 Brake fluid

*BF42.10-P-1001-01H

Brake fluid change unit

gotis://B_42/43.2_01

16

Install left front wheel



Remove/install wheels, rotate if necessary

AP40.10-P-4050RT

17

Lower vehicle using two-post lift

Two-post lifting platform 3.0-3.5 t, electromechanical
gotis://H_00.1_01.0

AR00.60-P-1000RT

18

Detach brake fluid replacement unit

Brake fluid change unit

gotis://B_42/43.2_01

19

Disconnect vacuum tester (1) from brake booster (3)

AR43.10-P-0024-01RT

 Test connection

*168589086300

 Vacuum tester

*201589132100

20

Close engine hood

AR88.40-P-1000RT

Number

Designation

Model
251

BE43.10-P-1002-01E

Brake pipe line pressure

Intake manifold
vacuum

Force on brake pedal

50 N

bar

26.5...32.5

0.75...0.8 bar

100 N

bar

50...57

150 N

bar

72...82

200 N

bar

95...107

250 N

bar

118...124

Number

Designation

Model
251
except
251.077/
177

Model
251.077/
177

BA42.10-P-1001-10L

Bleed screw to brake caliper

Nm

18

18

Number

Designation

Model
251

BA42.10-P-1001-12L

Bleed screw to brake caliper

Nm

7

Number

Designation

Model 251

BF42.10-P-1001-01H

Brake fluid

Filling capacity

Liters

0,8

Specifications for Operating Fluids

Sheet

BB00.40-P-0330-01A

Sheet

BB00.40-P-0331-00A