13. Rozdział 9 - Hamulce.pdf - Haynes Porsche 924 (MS1983) - zimny18stok

Chapter 9

Braking system

Contents

Brakes - general description

Brake master cylinder - removal and installation

Brake master cylinder - overhaul

Brake booster - removal and installation

Brake booster vacuum check valve - testing

Brake booster - checking

Front disc brakes - checking brake pad thickness

Front disc brakes - pad replacement

Front disc brakes - caliper removal and installation

Front disc brakes - rotor removal and installation

Front disc brakes - inspection of the rotor

Front disc brakes - caliper rebuild

Front disc brakes - rotor stripdown and assembly

Rear drum brakes - brake shoe inspection

Rear drum brakes - brake lining replacement

Rear drum brakes - backing plate stripdown and rebuild

Rear drum brakes - wheel cylinder rebuild

Bleeding the brake hydraulic system

Emergency brake - adjustment

Emergency brake - lever removal and installation

Emergency brake - lever stripdown and rebuild

Emergency brake - cable replacement

Specification

Brakes, 1976 to 1979 models

General

Hydraulic, disc front and drum rear with

cable operated parking brake utilizing

the trailing shoe within the brake drum

System type

Front brakes

Rotor type

Solid

Rotor diameter

10.12 in (257 mm)

Rotor thickness

New 0.512 in (13 mm)

Minimum, 0.472 in (12 mm)

Wear limit, 0.453 in (11.5 mm)

Pad thickness

New, 0.551 in (14 mm)

Wear limit, 0.079 in (2 mm)

Caliper piston diameter

1.690 In (48 mm)

Rear brakes

Brake drum diameter

New, 9.055 in (230 mm)

Maximum, 9.094 in (231 mm) using

oversize linings

Wear limit, 9.114 in (231.5 mm)

New std. 0.150 to 0.157 In (3.8 to 4.0

mm)

Lining thickness

New o/size, 0.169 to 0.177 in (4.3 to 4.5

mm)

Wear limit, 0.098 in (2.5 mm)

Wheel cylinder diameter

0.75 in (19.05 mm)

Hydraulic components

Brake booster

Diameter, 7 in (177.8 mm)

Boost factor, 2.5:1

Master cylinder

Diameter, 0.813 in (20.64 mm)

Stroke, 0.630 to 0.551 in (16 to 14 mm)

Recommended brake fluid

SAE J 1703 or DOT 3

Brakes, 1980 models standard system

As above except for:

Hydraulic components

Brake booster

Diameter, 9 in (228.6 mm)

Boost factor, 2.5:1

Master cylinder

Diameter, 0.937 In (23.81 mm)

Stroke, 0.669 to .590 in (17 to 15 mm)

Brakes, M-471 option

As 1980 standard system except for:

General

Hydraulic, disc front and rear, with cable

operated parking brake utilizing an

internally expanding shoe drum brake on

both rear wheels

System type

Front brakes

Rotor type

Ventilated

Caliper piston diameter

2.126 in (54 mm)

Rear brakes

Rotor type

Ventilated

Caliper piston diameter

1.417 in (36 mm)

Parking brake

Drum diameter

7.087 in (180 mm)

Wheels and tires, 1976 to 1979 models

Standard, stamped steel wheel

Wheel size

5 1/2 J x 14

Tire size

165 HR 14

Cold tire pressure, front and rear

2.0 bar (29 psi)

Optional, spoked cast alloy wheel (Standard US, 1979)

Wheel size

6 J x 14

Tire size

185/70 HR 14

Cold tire pressure, front and rear

1.6 bar (26 psi)

Winter tire recommendations

Standard wheel

165 SR 14 M +S

Optional wheel

185/70 SR 14 M +S

(Tire pressures as above, M+S = mud and snow)

Spare tire

All standard spare tires are the same as the wheels above, ie, standard wheeled cars have standard wheel mounted spares. The exception is

the 924 models with collapsible spare. This is mounted on a steel rim regardless of wheel type. Cars equipped with cast wheels and

collapsible spare have a spare set of mounting bolts appropriate to the steel wheel.

Wheels and tires, 1980 models

Standard, spoked cast alloy wheel (except Turbo)

Wheel size

6 J x 14

Tire size

165/70 HR 14

Cold tire pressure, front and rear

2.0 bar (29 psi)

Optional, 4-bolt cast alloy, wire wheel pattern (except Turbo)

Wheel size

6 J x 15

Tire size

205/60 HR 15

Cold tire pressure, front and rear

2.0 bar (29 psi)

Standard, 4-bolt cast alloy, wire wheel pattern (Turbo)

Wheel size

6 J x 15

Tire size

185/70 VR 15

Cold tire pressure

front 2.0 bar (29 psi)

Optional, M-471 option, 5 bolt mounting (all models)

rear 2.5 bar (36 psi)

Wheel size

6 J x 16

Tire size

205/55 VR 16

Cold tire pressure,

front 2.0 bar (29 psi)

rear 2.5 bar (36 psi)

Collapsible spare tire pressure (front or rear)

2.2 bar (32 psi)

Winter tire recommendations

All 924 except Turbo

165 SR 14 M+S on rims 51/2 J x 14

185/70 SR 14 M+S on rims 51/2 J x 14

or 6 J x 14

185/65 SR 15 M+S on rims 6 J x 15

All Turbo

165 SR 15 M+S on rims 5 1/2 J x 15

165/70 SR 15 M+S on rims 5 1/2 J x 15

or 6 J x 15

All 924 with M-471 option

205/55 SR 16 M+S on rims 6 J x 16

(Tire pressures as above, M+S = mud and snow)

Torque specifications

Parking Brake

ft-lb

m-kg

Parking brake lever to body

2.1

Brake cable to yoke

0.85

Parking brake cable to lock

0.85

Parking brake cable holder to drum brake backing plate

2.1

Brake Caliper (Front)

Bleeder screw to caliper

0.4

Guard to steering knuckle

1.0

Clamping nut with socket head bolt

9 to 11

1.3 to 1.6

Caliper to steering knuckle

8.5

Hydraulic hose to caliper

1.2

Wheel rim to brake disc (cast alloy)

Wheel rim to brake disc (steel)

Brake Drum (Rear)

Bearing cover and backing plate to diagonal arm

5.8

Brake cylinder to brake backing plate

2.1

Bleeder screw to wheel brake cylinder

0.4

Brake pressure line to brake cylinder

1.2

Parking brake cable holder to drum brake backing plate

2.1

Brake drum to wheel shaft (castellated nut)

217 to 289 30 to 40

Wheel rim to brake drum (cast alloy)

Wheel rim to brake drum (steel)

Hydraulic Components

Brake pressure booster to console

2.1

Stop light switch to dual master cylinder

14 to 22

2 to 3

Dual master cylinder to brake pressure booster

1.3

Brake pressure line to dual master cylinder, brake hose,

and distributor

1.4

1 Brakes - general description

1 The Porsche 924 models utilize an hydraulic system with vacuum boost for greater braking efficiency. A mechanical hand-brake is included.

2 From the beginning of production in 1976 through 1979 inclusive, all models are equipped with floating caliper, single piston, disc brakes

on the front and simplex (single leading shoe) drum brakes on the rear. For the 1980 model year, the M-471 package was included as an

option and utilizes ventilated rotor disc brakes from the 911 SC, aswell as floating caliper, single piston disc brakes with ventilated rotors on

the rear. Vehicles with this option installed will have five- bolt, 16 inch wheels.

3 In all models with simplex drum rear brakes, pulling up on the handbrake lever activates another lever within the brake drum housing. This

second lever presses the trailing edge (top edge) of the rearmost brake shoe against the surface of the brake drum. A cable connects the

handbrake lever to the parking brake actuating levers in each drum. The M-471 equipped models have small (180 mm) drum brakes included

in the rear brake assemblies which act as the parking brake. As in the previous type, they are activated via cable connection to the handbrake

lever.

4 Braking system circuitry is of the dual-diagonal type. Two complete braking circuits, consisting of separate chambers in the brake fluid

reservoir, brake master cylinder, one front brake and the rear brake on the side opposite, act together under normal operating conditions. In the

event of a failure in one of the braking circuits, depressing the brake pedal will cause a warning light to illuminate in the combination

instrument on the dashboard, alerting the driver; the front brake and the rear brake diagonally opposite in the undamaged circuit will slow the

vehicle in a straight line. This, in combination with the negative roll characteristic of the suspension (see Chapter 10) will ensure straight line

stopping of the vehicle while it is being driven to the nearest repair station. Under no circumstances should a vehicle with one damaged

braking circuit be driven, except to a place of repair. The impaired braking performance means that the vehicle will require greater distances

for stopping.

5 Under normal operation, depressing the brake pedal causes the dual master cylinder to pressurize by way of a connecting rod which passes

from the end of the brake pedal lever, through the vacuum boost unit and connects to the plunger on the master cylinder. Hydraulic pressure is

applied to the brakes in each circuit.

6 When ordering parts for your 924, be sure to provide the engine number, chassis number, year of manufacture, and model to your spare

parts supplier. If you intend your Porsche 924 for hard driving or competition use, your Porsche dealer will be best equipped to advise you on

modifications to improve braking performance.

7 Throughout the production life of the 924, several types of wheel have been offered. These may be broken into two specific types—cast

alloy and steel. Both types require a specific type of mounting bolt (see Fig. 9.1). A chart is provided, outlining the various available wheels.

2 Brake master cylinder - removal and installation

1 Raise the hood and disconnect the negative lead from the battery. If removal and installation of the master cylinder is to be done without any

work on the brakes, it is not necessary to raise the car or place it on stands. It is advisable, then, to set the parking brake and/or place the

transmission in gear (standard transmission models).

2 Remove the two electrical plugs from the stop light swiches on the underside of the master cylinder body. Place them out of the way so they

will not have brake fluid dripped on them. Some models have the wires bundled together and held with a nylon zip tie—if this is the case, it is

necessary to cut the tie to get the plugs far enough away from the master cylinder so they won't be dripped on.

3 Using a flare nut wrench, loosen the three brake line nuts on the master Cylinder body.

4 Place a drip pan beneath the car at the appropriate spot. Brake fluid wilt discolor and damage paint as well as being poisonous to pets and

people. Clean up any drips immediately.

5 Remove the two nuts which hold the master cylinder to the booster unit.

6 Double check the location of the electrical connectors.

7 Remove the nuts and flare connectors of the brake lines from the master cylinder body.

8 Remove the master cylinder body from the car (photo).

9 Pump the master cylinder piston rod several times while holding the master cylinder over a drip pan to purge excess brake fluid from the

assembly.

10 Before moving on to other tasks, make sure that no brake fluid has dripped onto any painted surfaces

11 Installation is the reverse of the removal process with the follow- ing points to be observed:

12 Torque the two nuts which hold the master cylinder to the booster unit to 15 ft-lb (2.1 m-kg).

13 After refilling the master cylinder it will be necessary to bleed the brake system (Section 18).

14 If the brake master cylinder has been removed only to gain access to the brake booster, make sure that the O-ring which seals the master

cylinder to brake booster join is not dried out and Is free from cuts, tears, and breaks. This will be replaced in the normal course of a master

cylinder rebuild but must be checked any time the master cylinder is removed.

3 Brake master cylinder - overhaul

1 When the master cylinder has been drained of excess fluid, place jaw protectors over the clamping jaws of a bench vise (or use wood

blocks) and clamp one of the flanges in the jaws with the stop light sender switches facing up.

2 Remove the two stop light sender switches with a wrench (photo). 3 Remove the master cylinder body and place it in the vise with the pump

rod facing up. Do not clamp the cylinder body In the vise jaws too tightly or deformation of the body will occur.

4 Remove the snap ring from the cylinder body at the pump rod end (photo).

5 Pump the pump rod up and down several times to free the washer and seal from the body, then remove the washer and seal. Note the

direction the lip of the rubber seal faces when installed in the body.

6 Remove the retainer bolt from the cylinder, body. It is located between the brake fluid reservoir and the cylinder body (photo).

7 Withdraw the pump rod and valve assemblies from the cylinder body. To aid in reassembly, lay out the various parts of the valve assembly

on a clean sheet of absorbent paper in the order in which they were removed.

8 Inspect the inner surfaces of the cylinder body for evidence of scratching, "chattering", gouges, and longitudinal scoring. Honing of the

cylinder walls may be done. Check with a qualified Porsche mechanic to determine inside diameter limits for your cylinder. If it is outside

specification a new cylinder body is necessary. Make sure the new cylinder body is one of the same manufacture as the brake booster.

9 If honing provides a useable cylinder surface within the tolerance, it will be necessary to flush the cylinder body and all orifices of the

cylinder with clean, new brake fluid. This will remove metal chips and other contamination. Do not use automotive cleaning solvents for this

job or any solvent containing mineral oils. Several brake cleaning solvents are now on the market. Check with your local automotive parts,

supplier before using any of these on your brake system components.

10 Place the cylinder body in the jaws of the vice. Do not overtighten the jaws and make sure they are covered with jaw protectors.

11 Open the master cylinder rebuild kit you have purchased and lay out the parts of the new kit alongside those you have removed. Note that

there are two thicknesses of seal cups which are not interchan- geable. There are also two springs which upon close inspection will prove to be

different. Separate these to avoid improper installation. There are also two different dust seal configurations available in rebuild kits. Each

may be replaced by a new dust seal of any other configuration, but only with all other rebuild parts from the same kit. If any rebuild parts

appear to be missing, obtain another kit from your parts supplier. Do not substitute old brake parts (photos).

12 Install the seal spacer in the smaller end of the tapered spring. Set it aside (photo).

13 Place one of the thin valve discs (washer) over the six holes of the valve body with the long, tapered, end adjacent the valve holes (photo).

14 Inspect the four seal cups. Note that one has a wider sealing surface (edge) than the others. Install this seal cup on the tapered end of the

valve body with the open end facing the taper and the closed end against the valve disc.

15 Lightly lubricate the installed seal cup and the three unmounted seal cups with clean, new, brake fluid.

16 Select the two unmounted seal cups which have sealing surfaces (edges) of the same width and install them in the two grooves at the end of

the valve body opposite the installed cup. The open ends of these cups should face the ends of the valve body with the closed ends facing each

other (photo). Set the completed forward valve assembly aside.

17 Place the remaining valve disc (washer) over the six valve holes at the stepped end of the rear valve body (photo).

18 Install the remaining seal cup against the valve disc with the open end facing the end of the valve body and the closed end against the valve

disc (photo).

19 Install the remaining seal spacer at one end of the constant-wound spring and place this assembly, seal spacer end first, into the seal cup of

the rear valve assembly (photo).

20 Install the shouldered bolt into the flange end of the travel limiting sleeve and then install it in the open end of the constant wound spring

(photos). Compress the spring and engage the threads of the bolt in the rear valve assembly. Tighten the bolt until the shoulder firmly contacts

the valve assembly. The lubricated assembly many be difficult to hold during tightening of the bolt. It may be held in a vise with protected

jaws for ease in tightening.

21 Lubricate the seal surfaces, piston rubbing surfaces, and inner cylinder surfaces with clean, new, brake fluid or brake assembly lubricant.

22 Insert the tapered spring, wide end first, into the cylinder body.

23 Insert the tapered end of the forward valve assembly into the center hole of the seal spacer (tapered end of the spring) and gently press the

assembly into the cylinder body (photo).

24 Install the rear valve assembly, spring end first, into the cylinder body. Press it in until only the hollow end of the pushrod shows over the

edge of the cylinder body (photo).

25 Lubricate the pushrod shaft with brake fluid. Install a metal washer, the rubber dust seal, and a second metal washer on the shaft (photo).

Compress the entire assembly until the locating groove for the circlip appears. Install the circlip (photo). Heavily lubricating the dust seal will

make compression of the valve assemblies much easier.

26 Remove the O-ring which seals the master cylinder to the brake booster. This is found in a shallow groove close to the master cylinder

mounting flange (photo). Install the new O-ring from the rebuild kit in the groove, A light coat of brake fluid will ease installation and prevent

damage to the seal when the master cylinder is reinstalled on the brake booster.

27 Before installing the rebuilt master cylinder in the car, bench bleed the cylinder. Place one of the mounting flanges of the master cylinder

in the protected jaws of the vise so that the brake fluid reservoir is in a full upright position. Partially fill the brake fluid reservoir with clean,

new, brake fluid. Pump the pushrod shaft in and out until all hydraulic connecting holes are pumping out brake fluid at the same rate. Note

that brake fluid is poisonous and will damage paint. Allow the brake fluid to run out but do not pump so hard and fast that fluid is sprayed

throughout the workshop.

28 Following installation of the rebuilt master cylinder, bleed the brake system (Section 18).

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