1973 OPEL GT-R light

CONTENTS
SubjectPage No.
DESCRIPTION AND OPERATION:
Power
BrakeBooster. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Master
Cylinder
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .DIAGNOSIS:
Power
Brake
,UnitTroubleDiagnosis. . . . . . . . . . . . . . . . . . . . . . . . . .MAINTENANCE AND ADJUSTMENTS:
Checking Brake Booster Operation
. . . . . . . . . . . . . . . . . . . . . . . . . . . .Brake Booster Filter Service
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Vacuum Control Valve Service
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .MAJOR REPAIR:
5A-2
5A-2SA-4SA-5
5A-65A-6
Brake Booster Removal and Installation
. . . . . . . . . . . . . . . . . .Master Cylinder Overhaul
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . * . . . . . . . . . . .SPECIFICATIONS:
General
Specifications
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .SA-6
5A-7
5A-95A. 21973 OPEL SERVICE MANUAL
POWER BRAKE BOOSTER AND MASTER CYLINDER
DESCRIPTION AND OPERATION
POWER BRAKE BOOSTERThe vacuum power cylinder contains the power pis-
ton assembly which houses the control valve and
reaction mechanism and the power piston return
spring. The control valve is composed of the air valveand the floating control valve assembly. The reaction
mechanism consists of a hydraulic piston, reaction
plate, and a series of springs. An air filter element is
assembled around the push rod and fills the cavity
inside the hub of the power piston. This keeps dirt
and dust from entering the vacuum booster. The
push rod, which operates the air valve, projects out
of the end of the power cylinder ‘housing through a
boot.MASTER CYLINDER
The master cylinder is composed pf a primary pistonand secondary piston; it is supplied with fluid from
two separate reservoirs. A check valve is mounted onthe primary circuit which supplies fluid to the rear
brakes. This keeps a slight static pressure in the rear
brake system. When the pedal is depressed, the pushrod moves the two pistons forward simultaneously
until the seals of the two pistons cover the compen-
sating ports in the cylinder. The pressure is increasedin the two chambers simultaneously, thus supplying
fluid to both front and rear brake systems.Figure
5A-1 Brake Booster Attachment (Opel 1900
and Manta)
In the GT, the brake fluid container is arranged at
right angles to the tandem brake master cylinder. SeeFigure
5A-3. It is pushed over the feed port of the
rear brake circuit onto the brake master cylinder and

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

POWER BRAKE BOOSTER AND MASTER CYLINDER5A- 7cylinder to brake booster and torque nuts to 14
Ib.ft.on the GT and 12
lb.ft. on the Opel 1900 and Manta.
2. Position assembly into brake booster bracket and,
on the GT only, thread piston push rod onto the
thrust rod.
3. Install brake booster to support attaching washers
and nuts and tighten to 11
lb.ft. of torque.
4. On the GT install master cylinder support to inner
fender skirt bolts.
5. Connect vacuum hose to brake booster.
6. By turning the piston push rod on the thrust rod,
(GT only) adjust until the brake pedal free travel is
l/4 inch and tighten the lock nut.
7. Connect brake pipes to master cylinder and bleed
brakes.
MASTER CYLINDER OVERHAUL. GT
Removal of Master Cylinder1. Disconnect the two brake pipes from the master
cylinder.
2. Remove the front support to skirt attaching bolts,
the cylinder to booster retaining nuts and lift out
master cylinder.
Disassembly1. Prior to brake master cylinder disassembly, pour
brake fluid out of brake fluid reservoir, remove reser-
voir from master cylinder and take sealing plugs out
of housing.
2. Screw static pressure valve(s) out of housing.
3. To facilitate disassembly, push piston somewhat
into cylinder and insert a rounded off piece of weld-
ing rod approx.
.12 in. thick into feed port to retain
piston in this position.
4. Remove stop screw and snap ring out of housing
and take out both pistons together with springs.
5. Remove stop screw from piston for rear brake
circuit and remove all component parts. Remove
also all component parts from intermediate piston of
front brake circuit.
Cleaning and Checking1. Clean parts with genuine brake fluid, Delco Su-
preme No. 11, or equivalent. Do not use any other
cleaning solvents. Dry with compressed air. Free up
compensating and feed ports.2. Polish cylinder bore of housing with crocus cloth.
If lapping scores and rust spots are still noticeable,
replace brake master cylinder assembly.
3. Check inner components for damage and replace,
if required. The rubber seals and static pressure valve
always have to be replaced.
Assembly1. Assemble front and rear brake circuit pistons.
Prior to assembly coat rubber seals with brake fluid.
2. Coat cylinder bore, piston sliding surfaces and
seals with brake fluid.
3. Insert preassembled intermediate piston for front
brake circuit together with thrust spring and spring
seat into clyinder bore. The smaller diameter of the
tapered thrust spring must face piston.
4. With a drift, push piston (against spring pres-
sure) into housing and insert a piece of welding rod
into feed port of front brake circuit to retain piston.
5. Install stop screw with new seal ring into housing
and tighten.
6. Insert preassembled piston for rear brake circuit
into cylinder bore and install snap ring into groove
in housing.
7. Check piston fof free movement by moving it to
and fro. If required, place washers under the head of
the stop screw.
8. Lightly push piston into housing and remove
piece of welding rod out of feed port of front brake
circuit.
9. With a rounded off piece of welding rod
(.020 -
,024 in.) check whether compensating ports are free.
10. Screw in new static pressure valve(s).
11. Coat new sealing plugs with brake fluid and in-
sert them into housing. Push twin brake fluid con-
tainer into sealing plugs and install screen and cover
with seal ring.
Installation1. Install master cylinder onto brake booster with
washers and nuts. Torque to 14
lb.ft.2. Attach the front mounting bracket.
3. Install brake lines on master cylinder, and bleed
brakes.

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- 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- 19
CAUTION:
Fasteners in Steps 7 and 9 are important
attachingparts in that they cooId affect theperfom-
ante of vital components and systems, and/or couJd
resuJt in major repair expense. They must be re-
placed with one of the same part number or with an
equivaJent part if repJacement becomes necessary.
Do not use a replacement part
or Jesser quaJity or
substitute design. Torque
vaJues must be used as
specified during
reassembJy to assure proper reten-
tion of these parts.7. Install brake disc on wheel hub and torque attach-
ing bolts to 36
Ib.ft. If old brake disc is reused, pay
attention to locator marks on brake disc and wheel
hub.8. Prior to installing brake disc and hub assembly to
steering knuckle, check lubrication of both roller
bearings and quantity of grease in cavity of wheel
hub. If necessary, repack front wheel bearings.
9. Adjust front wheel bearing clearance and tighten
brake caliper to steering knuckle, attaching bolts to
a torque of 72
lb.ft. Prior to installing brake caliper
to steering knuckle, ensure that all contacting sur-
faces are free of dirt and burrs. Also make sure that
the friction pads are not damaged when sliding the
brake caliper onto brake disc.
10. Install wheel assembly, remove supports and
lower front of car.
REMOVING AND INSTALLING
BRAKE DISC SHIELD
Removal
1. Remove brake disc.
2. Remove disc shield from steering knuckle by
removing one Phillips head screw on the outside and
on the inside, the lower steering arm and disc shield
to steering knuckle bolt. Remove paper gaskets from
steering knuckle. See Figure
5B-32.Installation
1. Prior to placing new paper gasket between brake
disc shield and steering knuckle, lightly coat both
surfaces of paper gasket with chassis lubricant.
2. Install disc and tighten disc shield and steering
arm to steering knuckle bolt to a torque of 47
lb.ft.CAUTION:
This steen;Og arm and steering knuckJe to
backing plate
fisteneris an important attachingpart
in that it
couJd at&t the performance of viral com-
ponents and systems, and/or
couJd resuJt in major
repair expense. It must be replaced with one of theFigure 58-32 Brake Disc Shield Attached
to SteeringKnuckle
same part number or with an equivalent part, if re-
pJacement becomes necessary. Do not use a rep/ace-
merit part of Jesser quaJity or substitute design.
Torque values must be used as specitied during reas-
sembly to assure proper retention of this part.3. Replace one Phillips head screw on outside of disc.
See Figure
5B-32.DISASSEMBLY AND ASSEMBLY
OF BRAKE CALIPER
1. Remove brake pipe from brake caliper. If both
calipers have to be repaired, it is advisable to mark
them with “L” or “R” on removal to avoid errors
when installing parts, such as pistons, etc. The brake
caliper halves must not be disassembled during re-
pair work. All work, such as pressing out pistons,
replacing seals in brake caliper, is carried out with
the two caliper halves bolted together.
2. Pry clamp rings from rubber seals, using a screw-
driver (Figure
5B-26) and remove rubber seals.
3. Remove piston first from caliper rim half (Figure
5B-33), and then out of the caliper mounting half
(Figure
5B-34) of the brake caliper, using mounting
clamp J-22429. To be able to force the piston out of
the caliper rim half, block the piston in the caliper
mounting half with mounting clamp J-22429 as
shown in Figure
5B-33. To force the piston out of the
caliper mounting half, place the mounting clamp on
caliper rim half, as shown in Figure
5B-34, and
tighten wing nut so that the rubber plate seals off the
caliper rim half bore. Then connect compressed air
hose to brake line connection in the caliper mounting

58.201973 OPEL SERVICE MANUAL
half, and blow out pistons, carefully regulating air
flow. When removing pistons, proceed with extreme
caution and always keep the fingers ofthe hand hold-
ing the brake caliper away from the piston.
Figure 55.33 Removing Caliper Rim Half Piston
Figure 58-34 Removing Caliper Mounting Half Piston
4. Pry rubber fluid seals out of the annular grooves
in the caliper half bores. See Figure
5B-35.5. Check all parts of the brake caliper for wear. If the
caliper half bores are scored or rusted, use a new
complete brake caliper and friction pads. Small, light
rust spots in the caliper half bores or on the pistons
can be removed with fine emery cloth. If pistons are
damaged, even though the caliper half bores are inFigure 58-35 Removing Rubber Fluid Seal From
Caliper Boresgood condition, the piston must be replaced. The
rubber fluid seals and rubber seals with
clapp rings
for the pistons are to be replaced every time repair
work is carried out on the brake caliper.
6. Thoroughly clean all reusable parts
- complete
brake caliper and pistons
- with denatured alcohol
and dry with compressed air. Prior to cleaning, screw
bleeder valve out of caliper.
7. Lightly coat new rubber fluid seals with brake
fluid and insert fluid seals into grooves of brake
caliper bores.
8. Place brake caliper into vise to install pistons.
After installing one piston, change position of brake
caliper in vise to install second piston. The piston to
friction pad spacer plates should be used as a gauge
to locate relieved edge of piston at 20 degrees to
horizontal during piston installation. See Steps
9-IO-
11-12.9. Place caliper mounting half in vise and coat its
bore and piston lightly with brake fluid. Then push
piston, with hollow end towards brake disc, into the
caliper bore. Turn piston so that the relieved edge
faces downwards at an angle of 20 degrees and facing
in brake disc direction. The guide surface in the
caliper half recess at the brake pipe connection side,
will properly align the piston. Push piston into
caliper bore up to the stop.
10. Change position of brake caliper and install sec-
ond piston in the same manner.
11. Install new rubber seals with clamp rings. Make
sure that the rubber seals are properly seated on the

DISC BRAKES5B- 21caliper half collars and the clamp rings are correctly
positioned on rubber seals.
12. Install brake caliper on steering knuckle, torqu-
ing bolts to 72 lb.ft.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.
CAUTION: This disc brake caliper attachments fas-
tener is an important attaching part in that it couldatExt the performance of vital components and sys-
tems, and/or could result in
ma@r repair expense. It
must be replaced with one of the
same part number13. Attach brake pipe to caliper and torque to 22
lb.ft.14. Bleed brakes as necessary.
SPECIFICATIONSDISC BRAKE SPECIFICATIONS
General Specifications
DiscBrakeType. . . . . . . . . . .
Location
..,,.,..__....__.,,.,,,................,,,................,....Disc Type
.._.......................................................I.-. -.
......................2 Piston Fixed Caliper - Disc
........................................Front Wheels Only
..............................................Solid Cast Iron
useuameter...................................................,..............................................................9.370Disc Lateral Runout (Maximum)
......................................................................................,004DiscThickness
(New).........................................................................................................430DiscThickness(Minimum)
................................................................................................,394DiscParallelism(ThicknessTolerance)
...........................................................................0006Brake Shoe and Lining Type
........................................................................................Bonded
Brake Shoe and Lining Thickness (New)
..........................................................................
,550Brake Shoe and Lining Minimum Thickness Before
Replacement
....................................................................................................................,280Disc Brake Master Cylinder Bore
.......................................................................................8 10Disc Brake Caliper Cylinder Bore
- GT..........................................................................1.770Disc Brake Caliper Cylinder Bore Opel
1900 and Manta..............................................
1.890Disc Brake Shoe Adjustment
..............................................................................Self-Adjusting
Torque Specifications
Use a reliable torque wrench to tighten the parts listed, to insure proper
tightness without straining or distorting parts. These specifications are for
clean and lightly-lubricated threads only; dry or dirty threads produce in-
creased friction which prevents accurate measurement of tightness.
Bolt
Bolt
Bolt
NutName
BrakeCalipertoSteeringKnuckle
BrakeDisctoWheelHub
Brake Disc Shield to Steering Knuckle and Steering
Arm.
Brake Pipe to Caliper
.,.,...............................,......................Torque
Lb.Ft.
72
36
47
22