Installation

Proceed in reverse order.

REMOVING AND INSTALLING SPEED SENSORS ON FRONT AND REAR AXLES

Removing and Installing

Front Axle

Removing

1. Take off front wheel. Remove intake hose on air cleaner.

2. Turn off ignition, take wire plug out of holder in engine compartment and disconnect.

4. Unclip wire on side member and in holders on steering knuckle.

Loosen socket head screw and pull speed sensor out of steering knuckle.

3. Remove front exhaust shield (to make procedures easier).

Unclip wires on wheel housings and pull out with rubber grommet in direction of wheel.

Also pull out rubber grommet for brake line.

Installing

Note:

— Rubber mounts and grommets on speed sensors are connected with wire covers in precise position.

— Take speed sensors out of protective packaging only briefly before installation (loss of permanent magnetism).

— Make sure that there are no foreign metal particles (burrs) on magnetic edge of speed sensor before installing.

1. Coat speed sensor and bore in steering knuckle with Molykote Longterm 2. Replace O-ring of speed sensor.

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2. Insert speed sensor in steering knuckle without application of force and tighten socket head screw to 10 Nm/7 ftlb.

Note:

The distance between speed sensor and pulse gear is given by design and cannot be adjusted.

3. Route wires correctly (insert rubber grommets and clip rubber mount in holder).

Install exhaust shield.

Connect wire plug and press into holder.

Install front wheel and intake hose.

4. Check operation with ABS tester.

Rear Axle

Removing 1. Take off wheel.

2. Turn off ignition, take wire plug out of holder and unclip wire on rear axle carrier.

3. Disconnect wire plug.

4. Unclip wire in holders on wheel carrier. Loosen socket head screw and pull speed sensor out of wheel carrier.

Installing

Note:

— Rubber mounts on speed sensors are connected with wire covers in precise position.

— Take speed sensors out of protective packaging only briefly before installation (loss of permanent magnetism).

— Make sure that there are no foreign metal particles (burrs) on magnetic edge of speed sensor before installing.

1. Coat speed sensor and bore in wheel carrier with Molykote Longterm 2. Replace O-ring of speed sensor.

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2. Insert speed sensor in wheel carrier without application of force and tighten socket head screw to 10 Nm/7 ftlb.

Note:

The distance between speed sensor and pulse gear is given by design and cannot be adjusted.

3, Clip wire in holders on wheel carrier and rear axle cross member.

4. Connect wire plug and insert in nolder. Install wheel.

5. Check operation with ABS tester.

REMOVING AND INSTALLING SPEED ONWARD

Front Axle

Removi ng l.With ignition switched off, ABS cable plug-in connector the steering knuckle and disconnect.

SENSORS ON FRONT AND REAR AXLES, 86 MODELS

l.Coat speed sensor and hole in steering knuckle with Molykote Longterm 2. Renew speed sensor 0-ring.

open on

2.Unscrew mounting bolt (Allen bolt) of speed sensor and withdraw sensor from steering knuckle.

Installing

Note:

- Do not remove speed sensor from its protective package until shortly before installation (loss of permanent magnetism)

- Before installation, check that no foreign bodies (metal shavings) have been caught on the magnetic edge of the speed sensor.

2.Without using force, insert sensor in steering knuckle and tighten Allen bolt to secure. (Torque 10 Nm (7ftlb)).

Note:

The distance between speed sensor and impulse ring is a design feature and cannot be adjusted.

3.Reconnect cable and place in holder on steering knuckle.

4.Check operation with ABS tester.

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Rear Axle Removing

1.Remove wheel.

2.With ignition switched off, open ABS cable plug-in connector on wheel carrier and disconnect cable. Open clip for speed sensor cable.

Unscrew speed sensor mounting bolt. Make space by withdrawing cable from holder above the mounting bolt.

3.Withdraw speed sensor from wheel carrier.

Installing

Note:

- Do not remove speed sensor from protective packing until shortly before installation {loss of permanent magnetism).

- Before installing, check that the magnetic edge of the speed sensor is free of foreign particles (metallic shavings).

l.Coat speed sensor and hole in wheel carrier with Molykote Long-term 2. Renew speed sensor 0-ring.

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2.Without using force, insert speed sensor in wheel carrier and tighten Allen bolt to secure. Torque: 10 Nm (7 ftlb).

Note:

The distance between speed sensor and impulse ring is a design feature and cannot be adjusted.

3,Place cable in clip on wheel carrier. Close clip. Insert cable in holder above sensor mounting bolt.

4.Insert plug-in connector and place in holder. Mount wheel.

5.Check operation with ABS tester.

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GENERAL

Braking System Until End of Model Year 1985

Until end of model year 1985 and depending on type and model year, the front-axle disk brakes use either sliding or floating calipers. All brake disks are ventilated. The brakes of the 928 S (with floating calipers) have auxiliary ventilation via air guide ducts. In all cars, sliding brake calipers are mounted on the rear axle. Brake pads with differing friction values are used. It is essential to ensure that the appropriate parts are installed (page 46 - 3).

Sliding brake caliper Floating caliper

Braking System, 86 Models Onward

Four-piston fixed-caliper brakes are fitted on front and rear axles instead of the sliding-caliper {floating or sliding caliper) systems installed in earlier models.

Four-piston fixed caliper

Brakes / Mech anicaI 928

TECHNICAL DATA

Description

Remarks

Wear

Specifications

Limit

Foot brakes

Hydraulic, dual circuit braking system

with disc brakes and diagonal division up to

end of 1983 models; axle circuit division

since 1984 models, brake booster, floating

frame caliper disc brakes on front axle and

floating frame or fist caliper disc brakes on

front axle.

Since 07.12.1977 to end of 1983 models

(diagonal division) one brake pressure

regulator for each rear axle circuit.

Since 1984 models one screw-in brake

pressure regulator on brake master

cylinder or on hydraulic unit (cars with

ABS) for rear axle brake circuit.

Since 1984 models optionally extra with

ABS, which is integrated in the con

ventional brake system.

Brake booster dia.

Up to 08.01.1979

9 inches

Since 09.01.1979

10 inches, internal ratio 3.0 for

floating frame caliper disc

brakes

10 inches, internal ratio 3.8 for fist

caliper disc brakes

Brake master cyl. dia.

Up to 1983 models

23.81 mm

Since 1984 models

23.81/19.05 mm

Brake pressure regulator

3 versions

Switching pressure for brake

pressure regulator

Version I

(9" brake booster)

55 bar

Version 11

(10" brake booster)

33 bar

Version III

(10" brake booster and

screw-in regulator)

33 bar

Caliper piston dia. Front

54 mm

Rear

36 mm

Brake disc dia. Front

282 mm

Rear

289 mm

Eff. brake disc dia.

Front — floating frame caliper

220 mm

fist caliper

228 mm

Rear

235 mm

Brakes/Mechanical

Description

Remarks Specification

Wear Limit

Pad thickness

Front, floating frame

13 mm

2 mm

floating caliper

13 mm

2 mm

Rear

13 mm

2 mm

New brake disc thickness

Front, floating frame

20 mm

grooved disc

20.5 mm

floating caliper

32 mm

Rear

20 mm

Min. thickness after machining *

Front, floating frame

19.2 mm

18.6 mm

floating caliper

31.2 mm

30.6 mm

Rear

19.2 mm

18.6 mm

Thickness tolerance for brake discs

max. 0.02 mm

Lateral runout for brake discs

max. 0.05 mm

Lateral runout for wheel hubs

max. 0.135 mm

Lateral runout for installed brake discs

max. 0.1 mm **

Max. surface finish of brake discs after

machining

max. 0.006 mm

Play on brake pedal with brakes bled

and engine stopped

10 mm

Hand brakes (parking)

Mechanical action on

both rear wheels

(drum brakes)

Brake drum dia.

180 mm

181 mm

Brake shoe width

25 mm

Brake surface per wheel

85 cm2

Brake liner thickness

4.5 mm

2 mm

* Brake discs must be machined symmetrically, i. e. evenly on both sides.

TECHNICAL DATA 86 MODELS ONWARD

Description

Foot brake

Remarks

Specifications

Wear Limits

Hydraulic, dual-circuit braking system with separate front/rear axle braking circuits (black/white), brake booster, ventilated brake disks with four-piston fixed calipers front and rear. Push-rod braking circuit for front wheels.

A braking-force regulator is bolted on the main brake cylinder or on the hydraulic unit {with ABS system) for the rear-axle braking circuit.

Anti-lock braking system (ABS), optional on 86 models, standard on 87 models onward. The ABS is integrated in the standard footbrake.

Brake booster

Brake master cylinder

Braking force regulator (screw-in regulator) Switchover pressure Reduction factor

(internal boost ratio)

87 models onward, pedal free travel is shorter

Tandem cylinder with 2 central valves

18 bar 0.46

Specifications

Wear Limits

Brake disk dia. front rear

304 mm 299 mm

Effective brake disk dia. front rear

250.8 mm 246 mm

Piston dia. in caliper front

86 models, each fixed caliper 2 x 42 + 2 x 36 mm

front

87* models onward each fixed caliper 2 x 44 + 2 x 36 mm

rear

each fixed caliper 2 x 30 + 2 x 28 mm

Pad surface per front wheel

Pad surface per rear wheel

86 cm2 424 cm2

Pad thickness front rear

13 mm 13 mm

2 mm 2 mm

Brake disk thickness new front rear

32 mm 24 mm

Fixed calipers with pistons of dia. 42/36 nun were installed in some cars (USA, Canada, Australia and Arabian countries) in the 1987 model year.

The front-axle brake calipers with 44/36 mm dia. pistons can be retrofitted in 86 models only in pairs.

Specifications

Wear Limits

Min. brake disk thickness* after machining front rear

30.6 mm 22.6 mm

30 mm 22 mm

Max. brake disk thickness tolerance

0.02 mm

Max. brake disk lateral runout

0.05 mm

Max. lateral runout of installed brake disk

0.1 mm**

Max. surface roughness after machining

0.006 mm

Play at brake pedal, brakes bled and engine stopped (footbrake arm without stop)

approx. 10 mm usually (i.e. without any means of support for foot-brake arm), determined by permanently set clearance at points inside braking unit

Parking brak e*** (handbrake)

Drum brakes applied mechanically on both rear wheels

Parking brake drum dia.

180 mm

181 mm

Brake shoe width

25 mm

Brake liner surface area per wheel

85 cm2

Brake liner thickness

4.5 mm

2 mm

Brake disks may only be machined symmetrically, i.e. evenly on both sides.

87 models onward, parking brake liners made of asbestos-free material (Energit 559). The liners can be retrofitted to vehicles earlier than model year 87 (right-hand and left-hand sides).

TORQUE SPECIFICATIONS FOR MECHANICAL PARTS OF BRAKING SYSTEM

Location

Description

Thread

Material

Torque Nm (ftlb)

Panhead screw of clamping nut

Allen-head screw

M 7

10.9

15 (11)

Brake caliper to steering knuckle

Hex screw/cap screw

M 12x1.5

8.8

85 (62)

Brake caliper to wheel carrier

Hex screw/cap screw

M 12x1.5

8.8

85 (62)

Floating caliper to bracket

Guide pin

M 9

15 - 20 (11 - 15)

Brake disk to wheel hub

Hex screw

H 6

8.8

10 (7)

Guard to steering knuckle

Hex screw

M 7

8.8

15 (11)

Locking pawl for handbrake to bearing bracket

Hex screw

M 8

8.8

25 (18)

Propshaft or rear axle to wheel hub

Locknut

VHM 22x1.5

8

460 (336)

Wheel to wheel hub

Wheel nut

M 14x1.5

Al

130 (95)

Location

Description

Thread

Material

Torque Nm (ftlb)

Locking pawl to handbrake lever

Locknut

M 8

8

23 (17)

Guard to wheel carrier

Locknut, Hex bolt

VFM 8 M 6

8 8.8

23 (17) 10 (7)

Speed sensor to wheel carrier and steering knuckle

Socket-head screw

M 6

8.8

10 (7)

0 0

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