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Home >> Mercedes Benz >> 2021 >> CLS450 4Matic >> Repair and Diagnosis >> Brakes >> Mechanical - Hydraulic >> Brakes - Pneumatic System - 257 Chassis >> Testing & Repair >> Checking Brake Booster - AR43.10-P-0325FR

Checking Brake Booster - AR43.10-P-0325FR

Model 257 

Model 290 

Shown on model 257 

G14548968Courtesy of MERCEDES-BENZ USA

Shown on model 257 

G14548969Courtesy of MERCEDES-BENZ USA
SPECIAL TOOL 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
REMOVING 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. NOTES
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.    
INSPECT 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.    
REFER TO SPECIAL TOOLS 000 588 01 82 00 Filling unit   WS25.00-P-0016B
REFER TO CAPACITIES & SPECIFICATIONS General brake fluid   BB00.40-P-0330-01A
REFER TO CAPACITIES & SPECIFICATIONS 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 
    SPECIAL TOOL Vacuum tester Fig 1
    SPECIAL TOOL Test connection Fig 2
11 Remove vent screw from front brake caliper on the driver's side and connect test equipment (7).    
REFER TO SPECIAL TOOLS 000 588 07 21 00 Test equipment   WS42.00-P-0014B
    NOTES
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. IMPORTANTCommercially available devices/tools 
Pedal force meter (8)
 
14 Start the engine and generate specified vacuum. IMPORTANT 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 If there is a problem,
↓
Switch off engine and check check valve (6).
*BE43.10-P-1004-01G 
      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
If there is a problem,
↓
Replace BAS brake booster (A7/7).
*BE43.10-P-1004-01G 
      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
    TORQUE SPECIFICATION Model 290 Bleed screw at brake caliper *BA42.10-P-1003-10BA 
    TORQUE SPECIFICATION Model 257 Bleed 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.    
REFER TO MAINTENANCE     AP42.10-P-4210B
25 Seal brake fluid reservoir using cap.    
INSTALLING Install     
26 Attach front wheel on driver's side.   AR40.10-P-1102A
27 Install support (2). TORQUE SPECIFICATION Screw/bolt, lower strut to suspension strut tower mounting bracket *BA62.30-P-1003-02K 
    TORQUE SPECIFICATION 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
Fig 1: Identifying Vacuum Tester (201 589 13 21 00)
G12939472Courtesy of MERCEDES-BENZ USA
Fig 2: Identifying Test Connection (168 589 08 63 00)
G12939475Courtesy of MERCEDES-BENZ USA
REPAIR MATERIALS

Number Designation Order number
BR00.45-Z-1028-04A Assembly cleaner A 000 986 56 01