Checking brake booster - AR43.10-P-0325V

MODEL 171.442 /456 /473

Fig 1: Checking Brake Booster

Courtesy of MERCEDES-BENZ USA

	Checking
1	Eliminate vacuum in BAS brake booster (A7/7)	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-1000V
3	Connect vacuum tester (030) with test connection (031) to BAS brake booster (A7/7)		AR43.10-P-0024-01V
		Brake booster Ø	*BE43.10-P-1001-01A
		Boost factor	*BE43.10-P-1002-01A
		Vacuum tester	Figure
		Test connection	Figure
4	Connect pressure tester (051) with connection fitting to brake caliper	Use the correct connection fitting (pitch, taper etc.), otherwise leakage and measurement errors will occur. Front axle:
		Bleed screw to brake caliper Rear axle	*BA42.10-P-1002-10P
		Bleed screw to brake caliper Pressure tester	*BA42.10-P-1002-12P
5	Attach pedal force meter (060) to brake pedal	Pedal force meter
6	Start engine and by opening the throttle produce a vacuum of 0.75 to 0.80 bar	If this vacuum is not reached or it drops immediately, the seal between the BAS brake booster (A7/7) and master brake cylinder may be damaged or the check valve (17) in the vacuum line (8) may be defective: ↓
		Checking check valve	AR43.10-P-0023V
		Remove/install master brake cylinder, replacing gasket	AR42.10-P-0310V
7	Apply the specified force to the brake pedal and read off the line pressure on the pressure tester (051)	In order to cover measurement errors (incorrect force on the brake pedal, incorrect vacuum) and scatter of the measuring devices, a tolerance of ± 10 bar on the specified value is permissible. The measured value must be within the value range.
		Brake pipe line pressure	*BE43.10-P-1003-01A
8	Detach vacuum tester (030) with test connection (031) from BAS brake booster (A7/7)
9	Detach pressure tester (051) with connection fitting from brake caliper
10	Remove pedal force meter (060) from brake pedal
11	Bleed brake system	Only bleed the brake caliper to which the pressure tester (051) was connected.	AR42.10-P-0010V
	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.
12	Check brake system for leaks		AR42.10-P-0100-01V

PNEUMATIC BRAKE BOOSTER TEST SPECIFICATIONS

Number	Designation					Model 171
BE43.10-P-1001-01A	Brake booster Ø				mm	177, 8/203
BE43.10-P-1001-01A	Brake booster Ø				inches	7/8
BE43.10-P-1002-01A	Boost factor					≈ 5.6
BE43.10-P-1003-01A	Brake pipe line pressure	Intake manifold vacuum 0.75- 0.8 bar	Force on brake pedal	50 N	bar	7.5...11.5
				100 N	bar	25...31
				150 N	bar	42.5...50
				200 N	bar	59.5...70
				250 N	bar	74...87

FRONT AXLE BRAKE CALIPER

Number	Designation		Model 171
BA42.10-P-1002-10P	Bleed screw to brake caliper	Nm	7

REAR AXLE BRAKE CALIPER

Number	Designation		Model 171 except 171.473	Model 171.473
BA42.10-P-1002-12P	Bleed screw to brake caliper	Nm	7	7

Fig 2: Identifying Vacuum Tester (201 589 13 21 00)

Courtesy of MERCEDES-BENZ USA

Fig 3: Identifying Test Connection (168 589 08 63 00)

Courtesy of MERCEDES-BENZ USA