Remove/install stepped tandem master brake cylinder

AR42.10-P-0310RT

Remove/install stepped tandem master brake cylinder

12.02.2019

Model

251

Modification notes

01.09.2010

"Perform brake test on test bench" reference changed

Test sequence augmented/revised

1

Partition wall between wheel well liners

9

Bracket

2

Bolts

10

Union nut of pressure circuit brake line

3

Bracket

11

Union nut of secondary brake circuit brake line

4

Water drain pipe

12

Nuts

5

Screw

13

Stepped tandem brake master cylinder

6

Screw

14

Electrical connector

7

Nuts

B34

ESP brake pressure sensor

8

Cover

13

Stepped tandem brake master cylinder

18

Impact deflector plate

15

Screw

19

Reservoir stop plug

16

Brake fluid reservoir

20

O-ring

17

Bolts

B34

ESP brake pressure sensor

 

Remove/install

 Caution

Risk of poisoning from swallowing brake fluid. Risk of injury from skin and eye contact with brake fluid

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

Topical note

Notes on externally invisible brake fluid loss

AH42.10-P-9406-02A

Topical note

Brake fluid notes

AH42.50-P-0001-01A

Topical note

Notes on repairs to brake system

AH42.00-P-0003-01A

1

Release vacuum in BAS brake booster

 To do this, press the brake pedal several times with the engine switched off.

2

Open engine hood and raise to vertical position

AR88.40-P-1000RT

3

Remove partition between wheel wells (1)

AR62.30-P-2400RT

4

Remove screw/bolts (2)

5

Remove holder (3)

6

Unclip water drain pipe (4)

 Installation: Ensure that water drain pipe (4) is correctly seated.

7

Remove screw/bolt (5)

8

Remove screw/bolt (6)

9

Unscrew nuts (7)

10

Lift up cover (8)

11

Remove bracket (9)

12

Unscrew union nut of pressure circuit brake line (10) and union nut of secondary brake circuit brake line (11) from stepped tandem brake master cylinder (13)


Seal connections with stop plugs,
in order to prevent brake fluid from escaping.

 Mark brake line relative to corresponding connection before unscrewing.

 Brake pipe to master brake cylinder

*BA42.10-P-1003-14A

 Box wrench bit

*140589000300

 Record plug

*129589009100

13

Unscrew nuts (12) from stepped tandem brake master cylinder (13)

 Check stepped tandem brake master cylinder (13) at rear primary piston for leaks.

 Nut, brake master cylinder to brake booster

*BA42.10-P-1001-05I

14

Detach stepped tandem brake master cylinder (13) from stud bolts and turn slightly to the side


Do not tilt stepped tandem brake master cylinder (13). Instead, pull it out forward straight
because otherwise, the push rod will be pushed out of its axial position and can break out of the retaining lugs on the master control unit.

15

Disconnect electrical connector (14) from ESP brake pressure sensor (B34)

16

Remove stepped tandem brake master cylinder (13)

 Installation: Replace O-ring (20).

17

remove bolt (15)

 Bolt, brake fluid reservoir to master brake cylinder

*BA42.10-P-1003-05I

18

Pull brake fluid reservoir (16) out of stepped tandem brake master cylinder (13)

 Installation:
Check reservoir stop plug (19) and replace if necessary
to avoid any leakage.

19

Remove screw/bolts (17)

 Bolt, impact deflector plate to master brake cylinder

*BA42.10-P-1002-05I

20

Remove impact deflector plate (18)

21

Remove ESP brake pressure sensor (B34)

 Brake pressure sensor to master brake cylinder

*BA42.45-P-1001-01K

22

Install in the reverse order

23

Bleed brake system

AR42.10-P-0010RT



Check

 Warning

Risk of accident from vehicle starting off by itself when engine running. Risk of injury (bruises and burns) resulting from working on the engine while it is being started or when it is running.

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

AS00.00-Z-0005-01A

24

Check brake system for leaks

AR42.10-P-0100-01RT

 Danger

Risk of death caused by limbs being caught or crushed by rotating parts when performing tests on the brake test stand

Never leave the vehicle unattended on the rollers except in an emergency. Ensure that no one is under the vehicle or near rotating parts during testing. In case of emergency, use the EMERGENCY OFF switch to shut down test stand.

AS42.00-Z-0001-01A

25

Carry out brake test on the test stand



AP42.00-P-4290BA

 Master brake cylinder

Number

Designation

Model 251

BA42.10-P-1001-05I

Nut, brake master cylinder to brake booster

Nm

25

 Master brake cylinder

Number

Designation

Model 251

BA42.10-P-1002-05I

Bolt, impact deflector plate to master brake cylinder

Nm

14

 Master brake cylinder

Number

Designation

Model 251

BA42.10-P-1003-05I

Bolt, brake fluid reservoir to master brake cylinder

Nm

4

 Brake hoses, brake lines

Number

Designation

Model 251

BA42.10-P-1003-14A

Brake pipe to master brake cylinder

Nm

18

 Electronic Stability Program (ESP)

Number

Designation

Model 251

BA42.45-P-1001-01K

Brake pressure sensor to master brake cylinder

Nm

35