Checking brake booster

AR43.10-P-0325FR

Checking brake booster

06.03.2020

Model

257

Model

290

Shown on model 257

1

Cover

2

Strut

A7/7

BAS brake booster

Shown on model 257

3

Vacuum line

4

Vacuum tester

5

Test connection

6

Check valve

7

Tester

8

Pedal force meter

A7/7

BAS brake booster

 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

Brake fluid notes

AH42.50-P-0001-01A

Notes on safety-relevant components

AH00.00-Z-0019-01A



Remove

1

Remove wiper arms.

AR82.30-P-6100FR

2

Remove cover (1) on driver's side.

3

Remove air/water duct.

4

Remove strut (2).

5

Remove front wheel on driver's side.

AR40.10-P-1102A

6

Clean area surrounding cap at brake fluid reservoir.


Before opening, clean the area surrounding the cap thoroughly.
Otherwise particles of dirt in the hydraulic components can result in malfunctions and total failure of the brake system.

Assembly cleaner

*BR00.45-Z-1028-04A

7

Unscrew cap from brake fluid reservoir.



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

8

Connect filling unit to brake fluid reservoir.



000 588 01 82 00 Filling unit

WS25.00-P-0016B



General brake fluid

BB00.40-P-0330-01A



Brake fluids (DOT 4 plus)

BB00.40-P-0331-00A

9

Remove vacuum in BAS brake booster (A7/7) by depressing brake pedal several times.

10

Connect vacuum tester (4) with test connection (5) at BAS brake booster (A7/7).

AR43.10-P-0024-01FR

 Vacuum tester

*201589132100

 Test connection

*168589086300

11

Remove vent screw from front brake caliper on the driver's side and connect test equipment (7).



000 588 07 21 00 Test equipment

WS42.00-P-0014B


Use correct connection fitting (pitch, centering cone, etc.).
Leaks and measurement errors can otherwise occur.

12

Bleed test equipment (7).

13

Connect pedal force meter (8) at brake pedal.

 Commercially available devices/tools
Pedal force meter (8)

14

Start the engine and generate specified vacuum.

 If this vacuum is not reached or it drops immediately, the seal between the BAS brake booster (A7/7) and the master brake cylinder may be damaged or the check valve (6) may be defective.

Brake line pressure

*BE43.10-P-1004-01G

If there is a problem,



Switch off engine and check check valve (6).

AR43.10-P-0023FR

15

Replace seal between BAS brake booster (A7/7) and master brake cylinder.

If the specified vacuum has not been reached or if it drops off straight away and the check valve (6) is not defective.

AR42.10-P-0300FR

16

Apply specified force to brake pedal and read off line pressure on test equipment (7).

Brake line pressure

*BE43.10-P-1004-01G

If there is a problem,



Replace BAS brake booster (A7/7).

AR43.10-P-0350FR

17

Switch off engine.

18

Remove pedal force meter (8) from brake pedal.

19

Remove vacuum in BAS brake booster (A7/7) by depressing brake pedal several times.

20

Disconnect vacuum tester (4) with test connection (5) from BAS brake booster (A7/7).

AR43.10-P-0024-01FR

21

Disconnect test equipment (7) with connection fitting and screw in vent screw all the way at brake caliper on the driver's side.

22

Bleed brake caliper on the driver's side.

AR42.10-P-0010-02FR

 Model 290Bleed screw at brake caliper

*BA42.10-P-1003-10BA

 Model 257Bleed screw at brake caliper

*BA42.10-P-1003-10X

23

Disconnect filling unit from brake fluid reservoir.

24

Check and correct fluid level in brake fluid reservoir.



AP42.10-P-4210B

25

Seal brake fluid reservoir using cap.



Install

26

Attach front wheel on driver's side.

AR40.10-P-1102A

27

Install support (2).

 Screw/bolt, lower strut to suspension strut tower mounting bracket

*BA62.30-P-1003-02K

 Screw/bolt, lower strut to firewall

*BA62.30-P-1004-02K

28

Install air/water duct.

29

Install driver's side cover (1).

30

Install wiper arms.

AR82.30-P-6100FR

Check values for pneumatic brake booster

Number

Designation

Model 257

Model 290

BE43.10-P-1004-01G

Brake line pressure

Vacuum 0.92…0.98 bar

Force on brake pedal

50 N

bar

22

22

100 N

bar

41

49

150 N

bar

61

75

200 N

bar

80

85

250 N

bar

100

87

 Front axle brake caliper

Number

Designation

Model 290

BA42.10-P-1003-10BA

Bleed screw at brake caliper

Nm

14

 Front axle brake caliper

Number

Designation

Model 257 (except 257.361)

Model 257.361

BA42.10-P-1003-10X

Bleed screw at brake caliper

Nm

14

14

 Frond end with front reinforcement

Number

Designation

Model 257

Model 290

BA62.30-P-1003-02K

Screw/bolt, lower strut to suspension strut tower mounting bracket

Nm

50

50

 Frond end with front reinforcement

Number

Designation

Model 257

Model 290

BA62.30-P-1004-02K

Screw/bolt, lower strut to firewall

Nm

23

23

Repair materials

Number

Designation

Order number

BR00.45-Z-1028-04A

Assembly cleaner

A 000 986 56 01