1973 OPEL GT-R service

POWER BRAKE BOOSTER AND MASTER CYLINDER5A- 5ConditionGrabby Brakes (Apparent
Off-and On Condition)
Possible Cause1. Broken or damaged
hydraulic brake lines.Correction1. Inspect and replace, as
“CXXSSary.2. Insufficient fluid in
master cylinder.
3. Defective master cylinder
seals.4. Cracked master cylinder
casting.2. Fill reservoirs with approved
brake fluid check for leaks.
3. Repair or replace, asnecessary.4. Replace
5. Leaks at front disc brake
calipers or rear wheel
cylinders
in pipes or connections.5. Inspect and repair, as
necessary.Brakes Fail to Release6. Air in hydraulic system.
1. Blocked passage in power
piston.
2. Air valve sticking shut.6. Bleed system.
1. Inspect and repair or replace,
as necessary.
2. Check for proper lubrication of
air valve “0” ring.
3. Broken piston return spring
3. Replace
master cylinder.
4. Tight pedal linkage.5. Repair or replace, as
necessary.
MAINTENANCE AND ADJUSTMENTS
CHECKING BRAKE BOOSTER OPERATIONThe operation of the brake booster can be checked by
simple means and without any special devices.
1. With engine off, first clear the booster of any
vacuum by depressing brake pedal several times.
2. Then depress brake pedal and start engine. If the
vacuum system is working correctly, the brake pedal,
kept under even foot pressure, moves farther down-
wards due to the additional pressure developed by
the booster. Should the brake pedal not move farther
downwards, the vacuum system is deficient. In this
case check the vacuum hose to booster, to vacuum
control valve and to engine intake manifold connec-
tions.3. If the vacuum system operates properly, the defect
is in the brake booster itself. A dirty filter impairs oreven prevents air from entering into the booster and
thereby the formation of a difference in pressure in
the vacuum cylinder.
Repairs cannot be carried out on the brake booster.
If no deficiency can be found in the vacuum system
or filter, the brake booster has to be replaced.
Under normal operating conditions the brake
booster requires no service. However, under adverse
conditions such as frequent driving on sandy or
dusty roads, the filter and sound deadener should be
replaced occasionally. To do so, the brake booster
must be removed but it isn’t necessary to detach the
master cylinder.
BRAKE BOOSTER FILTER SERVICEUnder normal operating conditions the filter need
not be exchanged for a new one.
Under adverse operating conditions
- frequent driv-

5A- 61973 OPEL SERVICE MANUAL
ing on dusty and sandy roads - the filter and sound
deadener should occasionally be replaced. To do so,
brake booster has to be removed without detaching
brake master cylinder.
Proceed as follows:
1. Remove protective cap (boot).
2. On the GT only, pry retainer from housing
using a screwdriver. See Figure
SA-6.Figure 5A-6 Brake Booster Filter (GT)
3. With a pointed tool remove air silencer and filter
out of control housing bore and pull it off thrust rod.
4. Install new filter and air silencer. On the GT, the
smooth side of the filter must face towards the inside.
The radial slots in filter and deadener must be stag-
gered to each other by 180 degrees.
5. Slide retainer over control housing (GT only) and
seal it with light plastic hammer strokes. Slide pro-
tective cap over control housing and slip it onto
brake booster housing.
VACUUM CONTROL VALVE SERVICE
A vacuum control valve is installed into the vacuum
hose between intake manifold and brake booster. It
serves to prevent air from flowing back (vacuum
release), when engine is shut off.
The vacuum control valve cannot be disassembled
and has to be replaced, if defective. On replacement,
note the following:
1. The vacuum control valve should be located near
the intake manifold. Therefore, the short vacuumhose has to be installed between intake manifold and
vacuum control valve and the long hose between
vacuum control valve and brake booster.
2. The arrows on the vacuum control valve housing
must point towards the intake manifold, otherwise
no air can be drawn out of the brake booster which
renders the brake booster ineffective.
3. The connections of the vacuum hoses to the intake
manifold, vacuum control valve and brake booster
must be airtight. For this reason make sure. that the
hose clamps are properly installed.
MAJOR REPAIR
BRAKE BOOSTER REMOVALAND INSTALLATION
Removal
1. Disconnect brake pipes from master cylinder.
Place a cloth under the master cylinder and brake
pipes to absorb any brake fluid drippings.
2. Disconnect vacuum hose from brake booster.
3. Remove four nuts and washers attaching brake
booster to brake booster support.
4. On the GT only, remove master cylinder support
to fender skirt bolts.
5. On the GT, loosen thrust rod lock nut and un-
screw the piston push rod while holding the master
cylinder brake booster assembly. On the Opel
1900and Manta, remove the nut and bolt attaching clevis
on the pedal.
6. Remove assembly from car.
7. Disconnect master cylinder from brake booster.
Installation
CAUTION: Fasteners in the folkwing steps are im-
portant attaching parts in that they could affect the
performance of vital components and systems, and-
/or could result in major repair expense. They must
berep/aced, with one of the same part number or with
an equivalent part if replacement becomes necessary.
Do not
use a replacement part or lesser quality or
substitute design. Torque values must be used as
specified during reassembly to assure proper reten-
tion of these parts.1. Using a new front housing seal, assemble master

5A- 81973 OPEL SERVICE MANUAL
4. If required, adjust mechanically actuated stop
light switch. Pedal travel of 5/S” to 1” should actu-
ate switch. Add or subtract washers between bracket
and switch to obtain proper adjustment.
5. Road test car for proper brake performance.
MASTER CYLINDER OVERHAUL. OPEL 1900
AND MANTA
Ramoval of Master Cylinder1. Remove master cylinder from brake booster by
disconnecting brake pipes and removing two
self-tightening nuts that secure master cylinder to brake;ia;;ter. Be careful not to loosen the front housing
Disassembly1. Prior-to brake master cylinder disassembly, pour
brake fluid out of brake fluid reservoir.
2. Remove reservoir from master cylinder body by
removing reservoir clips with snap ring pliers. See
Figure 5A-7.
Figure
5A-7 Removing Reservoir Clips
3. Remove the piston stop screw which is fitted in
master cylinder body.
4. Place master cylinder in a vise and push piston
forward and insert a rod with a spherical end into the
hole nearest the mounting flange. This will retain the
piston in a forward position and allow for removal of
snap ring. See Figures
SA-8 and 5A-9,Figure 5A.8 Retaining Piston in Forward Position
Figure 6A-9 Removing Snap Ring

5B- 10 1973 OPEL SERVICE MANUAL
DISC BRAKES
CONTENTS
Subject
DESCRIPTION AND OPERATION:
Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Operation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . * . . . . . . . . . . . . . . . . . .DIAGNOSIS:
DiscBrakeTroubleDiagnosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .MAINTENANCE AND ADJUSTMENTS:
Disc Brake Maintenance
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Checking Disc Brake Friction Pads for Wear
. . . . . . . . . .Replacing Friction Pads
Checking Brake Disc for Lateral
Runout. . . . . . . . . . . . . . . . . .MAJOR REPAIR:
RemovingandInstallingBrakeCaliper. . . . . . . . . . . . . . . . . . . . . .Removing and Installing Brake Disc
. . . . . . . , . . . . . . . . . . . . . . . . . .
RemovingandInstallingBrakeDiscShield. . . . . . . . . . . . . .Disassembly and Assembly of Brake Caliper
. . . . . . . . . .SPECIFICATIONS:
Disc Brake Specifications
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Page No.
58-1058-l
1
58-12
58-15
SB-15
5&17
56-17
58-17
58-195519
58-21
DESCRIPTION AND OPERATION
DESCRIPTIONThe front wheel disc brake consists of two major
parts: The brake disc and the brake caliper with the
two friction pads. See Figure
5B-20.The brake disc is attached to the inside of the wheel
hub flange by four bolts and centered on a shoulder
of the hub. The brake caliper consists of two halves:
the mounting half, arranged on the inside of the
brake disc, and the rim half. The two halves are
firmly attached to each other by four bolts. Two
flanges on the mounting half serve as attachment of
the brake caliper to the steering knuckle. The brake
caliper is positioned behind the front suspension
cross member at steering knuckle spindle level. It is
attached to the steering knuckle by two bolts. Both
caliper halves act as brake cylinders and each houses
a piston and a fluid seal. The fluid seal, of square
cross section, is positioned in an annular groove of
the caliper bore, preventing fluid leakage past the
piston and entry of water and dirt. The pistons and
caliper half bores are protected against entry of waterFigure 58.20 Left Front Disc Brake Assembly
and dirt in brake disc direction by a rubber seal, held
on the caliper half collar by a clamp ring and against

5B- 121973 OPEL SERVICE MANUAL
A = BRAKE ON
THE RUBBER FLUID SEAL TIGHTLY GRIPPING PISTON
IS DEFLECTED IN DIRECTION OF PISTON TRAVELAFRICTION PAD
BRAKE DISCRUBBER FLUID SEALBRAKE
IICALIPER
IPISTON
I
CE BETWEEN RUNNING CLEARAN
FRICTION PAD AND BRAKE DISC
B = BRAKE OFFBTHE PISTON IS RETRACTED BY THE AMOUNT OF
RUBBER FLUID SEAL DEFLECTION. THIS AMOUNT
IS EQUAL TO RUNNING CLEARANCE.SBZZ
Figure 58-22 Rubber Fluid Seal -Automatic Piston Retractiondraulic pressure, and the friction pads and pistonsmove away from the brake disc, leaving a small run-
ning clearance. The brake disc can now rotate freely.
The amount of brake travel is dependent upon the
amount of running clearance. For this reason therunout of the brake disc should be checked, besides
bleeding of the brake system and adjusting the rear
brake shoes, when the pedal free travel is too great.during braking, the rubber seals in the annular
grooves of the brake caliper bores deflect laterally in
the direction of piston movement. See Figure
5B-22,View (A). The seal remains deflected for the duration
of the braking operation. After braking, the caliper
bores are relieved of hydraulic pressure and the rub-
ber seals resume their normal position, thus pulling
or retracting the pistons. The distance traveled by
the pistons is equal to that of the running clearance
between brake disc and friction pads.
The running clearance between brake disc and
fric-tion pads is attained as follows: When the pistons in
the caliper halves are moved towards the brake discThe shifting of the pistons in the direction of the
brake disc due to friction pad wear has no effect on
the running clearance. The running clearance re-mains the same in all piston positions.
DIAGNOSIS
DISC BRAKE TROUBLE DIAGNOSIS
ConditionPulls
Possible Cause
I. Incorrect tire
pressures.Correction1. Inflate evenly on both sides to
the recommended pressures (see
Owner’s Manual).

5B- 141973 OPEL SERVICE MANUALConditionPossible CauseCorrection2. Partial system failure.2. Check front and rear brake system
and repair, if necessary. Also, check
brake warning light, if a failed
system is found and light did not
function.
3. Excessively worn shoe
and lining.3. Check and replace in axle sets.
4. Piston in caliper stuck
or sluggish.4. Remove caliper and rebuild.
5. Fading brakes due to
incorrect lining.
6. Vacuum leak.5. Remove and replace with original
equipment lining.
6. Check for ruptured hose or loose
attachment.
Excessive Pedal Travel1. Partial brake system
failure.1. Check both front and rear system
for a failure and repair. Also, check
warning light
- it should have indi-
cated a failure.
2. Insufficient fluid in
master cylinder.
3. Poor rear brake
adjustment.2. Fill reservoirs with approved
brake fluid. Check for leaks.
3. Adjust rear brake per
specifications.
4. Air trapped in system.4. Bleed system.
5. Bent shoe and lining.5. Replace axle set of shoe and
lining.
Dragging Brakes (A very
light drag is present in
all disc brakes
immediately after pedal
is released.)1. Master cylinder pistons
not returning correctly.1. With reservoir cover off, check
for fluid spurt at bypass holes as
pedal is depressed. Adjust push rod,
if necessary, or rebuild master
cylinder.
2. Restricted brake tubes2. Check for soft hoses or damaged
or hoses.tubes and replace with new hoses and
new double-walled steel brake tubing.
3. Incorrect parking brake
adjustment on rear brakes.3. Check and readjust to correct
specifications.
Grabbing or Uneven Braking
Action (All conditions
listed under “Pulls”
.)4. Check valve installed in
outlet to front disc brakes.
1. Malfunction of power
brake unit.4. Check master cylinder outlet and
remove check valve if present.
1. Check operation and repair, if
necessary.

DISC BRAKES5B- 15
ConditionPossible Cause
2. Binding brake pedal
mechanism.Correction
2. Check and lubricate, ifnecessary.3. Corroded caliper
assembly.3. Clean and lubricate.
MAINTENANCE AND ADJUSTMENTSDISC BRAKE MAINTENANCE
Checking Brake Fluid Level
The brake fluid level in the brake fluid container
must be checked during predelivery inspection, then
every 3,000 miles during inspection and preventive
maintenance servicing.
The brake fluid level must not be higher than the
inscription “MAX” and must be at least up to
“MIN”. Replenish brake fluid, if necessary.
Because of the relatively large brake caliper bore
cross section and the self-adjustment of the disc
brakes, resulting in a greater piston travel to compen-
sate for friction pad wear, the brake fluid level drops
faster than in fluid containers for drum brakes with
their smaller wheel brake cylinders. For this reason
pay special attention to the fluid level in the brake
fluid container.
Drop of brake fluid level can be due to friction pad
wear and may not be due to leakage in the braking
system.On loss of brake fluid due to leakage, the brake sys-
tem must be checked thoroughly.
Friction Pad Adjustment
Friction pad adjustment is not necessary on the front
wheel disc brakes as this is done automatically by the
pistons in the brake calipers.
Lubricating Front Wheel Bearings
When removing one or both brake discs, check lu-
brication of front wheel bearings and the cavity of
the wheel hub and replenish if necessary (see operat-
ion
“Removing and Reinstalling Brake Disc”).
When carrying out other work on disc brakes which
does not necessitate the removal and installation of
the brake disc, lubricating wheel bearings is not
necessary.Checking Disc Brake Friction Pads for Wear
Whenever a disc brake equipped car is in for periodic
service, while the car is raised, the friction pads in
both brake calipers should be checked for wear by
making a simple measurement. Worn or oily friction
pads must be replaced.
Measure friction pad wear as follows:
1. Remove friction pads.
2. Using a one-inch micrometer, measure the thick-
ness of the pad and friction plate. See Figure
5B-23.Figure 58-23 Checking Brake Friction Pad Thickness
3. If any one of the four measurements is less than
-.280, replace all four friction pads. (Partial replace-
ment of friction pads would cause unequal braking.)
Removal and Installation of Friction Pads
1. Raise car and remove front wheels.
2. Drive dowel pins out of brake calipers toward
center of car. See Figure
5B-24. Dowel pins must be
driven inward because they are secured by enlarge
fluted inner ends.
3. Remove friction pads from brake calipers. See
Figure
5B-25.

5B- 19i973 OPEL SERVICE MANUAL
Figure
56-24 Removing Dowel Pins
Figure 56-25 Removing Friction Pads
4. Check rubber seals for wear. If rubber seals are
hardened, brittle or cracked, they must be replaced
as follows:
(a) Remove brake caliper from steering knuckle and
brake disc. Leave hose attached to brake caliper.
(b) Remove seal clamp rings with screwdriver and
remove seal rings from calipers. See Figure
5B-26.(c) Install new rubber seals and clamp rings. Make
sure rubber seal is properly seated. Make sure clamp
ring is correctly positioned on rubber seal,Figure 56-26 Removing or Installing Rubber Seal
Clamp Ring
(d) Attach brake caliper to steering knuckle and
torque bolts to 72
Ib.ft. Prior to installation of
caliper, make sure contacting surfaces of both caliper
and steering knuckle are perfectly clean and free of
any burrs.
CAUTION: This disc brake caliper attachments fas-
tener is an important attaching part in that it could
affect the performance of vital components and sys-
tems, and/or could
result in major repair expense. It
must be replaced with one of the same part number
or with an equivalent part, if replacement
becomes
necessary. Do not use a replacement part of lesser
quality or substitute design. Torque values must be
used as specified during reassembly to assure proper
retention of this part.5. Before installing new friction pads, press both pis-
tons of each caliper to bottom of their bores, using
Return Clamp J-22430.
While pressing piston into
bores, open caliper bleeder valve to prevent excess
brake fluid from overflowing master cylinder con-tainer As soon as pistons are bottomed, tighten
bleeder valve.
6. Check brake disc for lateral runout.
7. Install new friction pads into brake caliper. Fric-
tion pads must be free enough to be easily moved in
their caliper recesses. See
Figure X3-25.If new friction pads are not free, it will be necessary
to remove pads and clean recesses and recess corners
with a wooden spatula and then with denatured al-
cohol and a brush. After cleaning, blow out recesses
with compressed air. Remove any high spots on
edges of friction pads contacting caliper recesses with