Brake System Service Mercedes Benz

Master cylinders manufactured by ATE, Girling and Bendix utilize 2 or 3-chamber reservoirs, a level sensor contact is built into each chamber.

A warning light is activated when brake fluid level is low or when pressure differential between two brake circuits is caused by loss of fluid in either circuit.

Floating type front disc brake calipers are used on the 190, 420 and 560 series; Not floating type calipers on other models with parking brakes are cable-actuated in rear brake rotor calipers.

All models have brake pad wear indicators and differential pressure warning indicator.

Wear sensors for 420 and 560 series operates on inner pads only.

The Anti-Lock Brake System is standard on 420SEL, 300 and 560 series (optional on 190 series).

On diesel models, a vacuum pump is incorporated to supply a vacuum to the power brake unit.


Pedal height measured from pedal pad to pedal stop should be 150 m.m.

to adjust loosen lock nuts and turn stop light switch until correct pedal height is obtained tighten lock nuts; pedal free play should be 5-15 m.m..


The stoplight switch is located under dash, above brake pedal loosen lock nuts and adjust switch so that contact button extends 6-8 m.m. then tighten lock nuts.


1. Remove only one wheel lug bolt at each rear wheel, raise vehicle.

2. Rotate wheel until lug bolt hole is positioned over parking brake adjuster, approximately 45 degrees forward for diagonal swing axle and 90 degrees forward for diagonal swing axle with starting torque compensation.


Parking brake must be adjusted if brake pedal can be depressed by more than 2 steps of 6 without any braking effect, do not alter adjusting screw on parking brake intermediate lever; these screws are for balancing cable lengths only.

3. Using screwdriver inserted through lug bolt whole hand turn adjuster until rear wheel cannot be turned, back off the adjuster until wheel can be turned without wheel dragging.


1. Dual warning light is mounted on dash, turn ignition on and the light should glow when parking brake lever is pulled to one notch and go off when brake lever is fully released.

2. To check circuit warning sensor, turn ignition on, release the parking brake and ensure light is off,

Open bleeder screw on one wheel and depress brake pedal and the light should light up.

3. Close bleeder screw, replenish the brake fluid and bleed system, check that light goes out after testing and if not; differential pressure pin in the master cylinder must be reset.


Removal 420SEL, 300 & 560 Series

1. Raise vehicle and remove wheels, remove upper hex head caliper bolt.

2. Pull clip of the brake pad wear sensor out of plug by opening cap on plug, rotate caliper downward and remove pads from carrier.

3. Standard front disc brake pad   assembly  thickness including lining backing plate is 17.5 m.m. Standard rear pad  assembly  thickness is 15.5 m.m..

4. Front backing plate thickness is 4.5 m.m. Rear backing plate thickness is 5mm Minimum pad thickness is 2 m.m..

Mercedes Benz Single Piston Disc Brake Caliper cleaning.

1. Using brass cylinder brush clean disc pad guide surface in caliper, siphon fluid from master cylinder to prevent overflowing press piston to bottom of bore.

2. Install disc pads and wear sensor wires, reverse removal procedure to complete installation and check that dash light goes out.

Removal All Other Mercedes Benz Models

1. Raise vehicle and remove wheels, remove cover plate from caliper and disconnect wear indicator wires.

2. Drive out retaining pins toward inside of vehicle, on Bendix brakes retaining pins have locking pins, then remove the locking pins and retaining pins then the cross spring retainers.

3. Remove disc pads from caliper, if not reusable note condition and location of pads for re installation.

4. Standard front disc brake pad  assembly  thickness including lining backing plate is 17.5 m.m. Standard rear pad  assembly  thickness is 15 m.m..

5. Front backing plate thickness is 4.5 m.m. rear backing plate thickness is 5 m.m. minimum pad thickness is 2 m.m..

1. Using cylinder brush clean disc pad guide surface in caliper, siphon fluid from master cylinder reservoir to prevent overflowing, press pistons to bottom.

2. Mercedes Benz Disc Brake Pads.

3. Install cover plate retaining pin locking keys and wear sensor wires, check that dash light goes out, and the reset pin at master cylinder.


1. Raise and support vehicle remove the wheel, open bleeder screw on caliper  assembly  and pump out fluid, disconnect and plug brake lines at caliper  assembly .

2. Remove caliper bolts, remove caliper  assembly  from vehicle.

Installation To install reverse removal procedure, tighten all nuts and bolts and then bleed hydraulic system and check that the dash light goes out, reset pin in master cylinder if necessary.


1. Remove caliper  assembly  and hub grease cap, remove contact spring for radio shielding, loosen clamping nut socket screw on wheel spindle.

2. Remove clamping nut and washer, remove wheel hub and rotor  assembly , remove bolts securing hub to rotor, remove rotor.

Cleaning & Inspection

1. Clean disc and check for cracks, scoring or excessive wear, replace as necessary.

2. Before installing stock replacement disc, use solvent to remove nitrocellulose corrosion preventive paint from rotor surface.

Installation To install reverse removal, tighten all bolts and fittings evenly, bleed hydraulic system if necessary, lubricate and adjust wheel bearings, see appropriate article in suspension section.

Removal rear brakes

1. Remove rear wheel and tire and disconnect and plug brake lines, remove caliper  assembly .

2. Using rear axle shaft  Assembly  Tool 116 589 24 61 00, pull rotor out from axle shaft flange.

1. To install reverse procedure, coat the axle splines with high temperature lubricant grease wheel bearings and install seal if necessary.

2. Tighten all bolts and fittings evenly and bleed hydraulic system.


1. Remove rear wheel and tire and release locking plates, remove mount bolts and caliper, wire caliper out of the way.

2. On vehicles with starting torque compensation, disconnect brake hose holder and hang caliper  assembly  with wire.

3. Loosen and remove 8 m.m. bolt or 12 m.m. bolt with spacing sleeve and clamping disc at center of rear brake rotor.

4. Using rear axle shaft  Assembly  Tool, remove rotor from rear axle shaft flange and pry rear axle seal from rotor at inner wheel bearing and discard.

If the brake rotor is difficult to free from the axle flange strike the outer circumference lightly with a plastic hammer and ensure parking brake is released.


1. Coat inside of new axle seal lip and wheel bearings with grease, install bearings and seal into rear brake disc.

2. Coat axle splines with heat resistant lubricant and install disc, to complete installation reverse removal procedure.

Mercedes Benz master cylinder removal

1. Drain master cylinder fluid and disconnect and plug brake lines, disconnect electrical wires.

2. Remove the bolts securing master cylinder to power brake unit and remove master cylinder.


1. Reverse procedure; always replace rubber “O” ring seal between master cylinder and power unit.

2. Bleed hydraulic system and check complete system for fluid leaks, check that dash light is out and reset pin in cylinder.


1. Remove wheel and tire and disconnect hydraulic line, remove caliper and disc and turn the rear axle flange until the threaded hole faces down, compress spring with spring and turn 90 degrees.

2. Remove all retainers and hold-down springs, detach lower return spring opposite adjuster and pull brake shoes apart enough to remove over rear axle shaft flange, detach upper return spring and remove adjuster.

Cleaning & Inspection Use brake vacuum cleaner to clear asbestos dust from  assembly  and check condition of linings and components.

Disc brake rotor inside diameter is 160 m.m. parking brake lining width 25 m.m..


1. To install reverse procedure, lubricate all adjuster components and sliding surfaces of backing plate with silicone brake grease.

2. Return adjuster to position and install on shoes with adjusting wheel facing 45 degrees forward diagonal swing axle or 90 degrees forward diagonal swing axle with starting torque compensation.

3. Attach hold down springs and retainers and return springs, install disc and adjust parking brake.


Removal Diesel Only While holding lock nuts loosen vacuum lines from pump, detach hex head mount screws from crankcase and remove vacuum pump and gasket.

Piston type vacuum pump screw connector is provided with oil retention valve, when pump is stopped and vacuum is available, valve prevents engine oil from entering power brake unit.

Installation Install vacuum pump with new gasket to crankcase, the new gasket thickness is 2 m.m. Connect vacuum lines and test for proper operation.


1. Loosen upper radiator hose and drain some coolant and remove the fan radiator shell and power steering pump belt.

2. Loosen vacuum lines from pump; remove hex head mount screws from crankcase remove vacuum pump with toothed intermediate sleeve and gasket.


1. Clean sealing surfaces and install pump with new gasket to crankcase and ensure intermediate sleeve and pump locating pins are properly seated in crankcase.

2. Connect vacuum lines to pump, install belt radiator shell, fan and hose, check pump for proper operation.


Disassembly 420SEL, 300 & 560 Series

Remove caliper from vehicle and place piece of wood in front of piston, gradually apply compressed air into fluid inlet remove piston and remove dust boot from piston and piston seal from caliper bore.

Cleaning & Inspection

1. Wash parts in alcohol or brake fluid and air dry, inspect caliper bore and piston for scoring scratches or rust, standard front brake caliper bore inside diameter is 60 m.m..

2. Replace dust boot and piston seal when disassembling caliper, remove small rust deposits in bore with fine cloth.

When installing new caliper and check that calipers on same axle have pistons of same diameter, only identical calipers should be installed on front axle.

Reassembly Coat piston and caliper bore with ATE brake cylinder paste, install piston seal into caliper bore and install piston and dust boot.

Disassembly 190, 300E, 300SDL & 420SEL this procedure also applies to all rear calipers.

1. Remove caliper from vehicle and remove disc pads from caliper and remove dust boot.

2. Hold one piston in place using piston Resetting Pliers, gradually apply compressed air to fluid inlet to remove opposite piston.

3. Remove piston seal from groove of cylinder bore and remove remaining piston and seal in same manner. DO NOT separate caliper halves, replace only as an  assembly , calipers installed on front axle must be from same manufacturer.

Calipers on rear axle may be different only if same brand replacement part is unavailable.

Cleaning & Inspection

1. Check cylinder bores of caliper for wear or damage, small rust deposits may be removed from caliper bores with cloth.

2. CAUTION: DO NOT clean chrome-plated surfaces of pistons with polishing or emery cloth damage to surface may result.

Remove deposits with soft brass wire brush or rough cleaning cloth, replace piston if chrome surface is damaged.

2. Heavy rust deposits or badly scored bore will require replacement of the caliper rust deposits in front of piston seal groove may be removed with fine emery cloth.

3. Standard front brake caliper bore inside diameter is 60 m.m. Standard rear caliper bore I.D. Teves is 38 m.m. and rear caliper bore I.D Bendix Girling is 42 m.m..


1. Coat piston and caliper bore with ATE brake cylinder paste, install piston seal into the caliper bore and then install piston.

2. With caliper installed on the diagonal swing axle elevation on the piston faces upward.

On diagonal swing axle with starting torque compensation, elevation on piston must be at bottom and project at least 10 m.m. above shield, use DOT 4 or higher rated brake fluid during the overhaul.

2. Check position of piston in caliper with Piston Gauge for front or for rear.

3. Adjust with Piston Rotating Pliers and install dust boot, install heat shield into piston with recess in shield fitting into elevation of the piston.


Overhaul procedure is the same as front caliper of 300E, 300SDL and 420SEL models.


BENDIX master cylinder painted Blue cannot be overhauled and replace as an  assembly  only.

Disassembly Tandem & Stepped Tandem

1.On tandem master cylinder remove the reservoir and push piston in

remove stop screw; remove the push rod piston  assembly  and O ring.

2.Remove the lock ring from housing and remove the floating circuit piston, and stop washer with two vacuum seals and intermediate ring.

3.Tap lightly on housing with plastic mallet to remove the floating circuit piston  assembly .

On Teves reservoir only remove cap end covers and strainer and splash guard, O rings and contact the inserts.

On Bendix models, remove strainer from cover, DO NOT remove the contact inserts.

Always use DOT 4 or higher brake fluid during overhaul.


Cleaning & Inspection

1.Clean all parts with alcohol or brake fluid and flush residue out of housing, check bore in housing and the piston for score marks and rust.

2. Small rust spots in housing may be removed with emery cloth scored or badly rusted parts cannot be repaired and require replacement of complete master cylinder.

3.On tandem models with standard master cylinder inside diameter is 23.81 m.m. maximum bore wear limit is 23.92 m.m..

4.On the stepped tandem models, standard master cylinder I.D. for push rod circuit is 23.81m.m. and I.D. for floating circuit is 19.05 m.m..

5. Maximum master cylinder bore I.D. is 23.92 m.m. for push rod circuit and 19.16 m.m. for floating circuit.


1. To assemble reverse disassembly procedure, coat the bore of master cylinder with brake fluid.

2. Install new floating circuit piston  assembly  and push in piston  assembly  and install lock ring.

3. Install the new push rod piston  assembly  and screw in stopper screw using new copper washer for Gray iron master cylinder or new aluminum washer for light alloy master cylinder.

Replace O ring to ensure proper vacuum seal at power brake unit and bleed hydraulic system, check that the dash light is out.

Differential pressure warning indicator reset pin located at the front end of master cylinder MUST be reset once and indicator light in dash panel has been triggered.


Manufacturer does not recommend disassembly of this unit, if problem is found in power brake unit complete  assembly  must be replaced, DO NOT disassemble power brake unit, determine whether source of problem is in power brake unit or the check valve.