From model '83 REMOVING AND INSTALLING BRAKE BOOSTER AND BRAKE MASTER CYLINDER 1 Pump 2 Oil tank 3 Pressure controlled flow regulator 4 Hydraulic reservoir 5 Steering 6 Hydraulic booster 7 Tandem master cylinder |  |
Description of Entire H 31 System: The "pressure controlled flow regulator (also referred to as pressure regulator) taps a slight delivery flow = 0.7 ltr. (1.5 pints)/minute from the operating circuit of the power steering (circulating system) for the hydraulic brake booster (reservoir system) and charges the hydraulic reservoir in a pressure range without impairing the function of the power steering. The hydraulic oil volume stored under pressure is available for the booster to support the operating force and is called by operating the bolted standard tandem brake master cylinder. If the power steering pump fails, sufficient reserve pressure will be stored in the hydraulic reservoir to be able to execute several braking actions with full brake boosting support. After consumption of this reserve pressure, the brakes can still be applied, but without boost and therefore considerably more force on the brake pedal. | |
Function Test: Operate brake pedal 20 times with engine stopped. Hold brake pedal down and start engine. System is okay, if brake pedal gives. If brake pedal does not give, the power steering pump, power flow regulator, hydraulic reservoir or hydraulic brake booster could be defective. | |
Removing and Installing Brake Booster with Brake Master Cylinder: Discharge hydraulic reservoir by operating brake pedal about 20 times with same force required for full stop braking action with engine stopped. Draw off brake fluid through supply tank with a syringe reserved exclusively for brake fluids. |  |
Remove instrument panel trim at bottom left - see 51 45 180. Lift out bayonet clip (1) and remove pin (2) on piston rod.  51 45 180
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Disconnect brake lines. 1 Front right 2 Front left Installation: Tightening torque*. Bleed brakes - see 34 00 046. 34 00 046 * See Specifications
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Detach hydraulic hoses on brake booster. Installation: Make sure that all pipe and hose connections are clean before connecting. Tighten return line with Special Tool 34 3 153 and pressure line with Special Tool 34 3 152, both in conjunction with a torque wrench. Tightening torque*. * See Specifications
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Detach brake booster on pedal assembly base. Remove brake booster and brake tandem master cylinder. Installation: Tightening torque*. * See Specifications
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Detach master cylinder on brake booster to replace brake booster. Installation: Tightening torque*. * See Specifications
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Installation: Detach pivot on brake booster. Attach point on new brake booster and adjust to same distance B. If necessary, check distance A on brake pedal in installed state (see 35 21 000). 35 21 000
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