Page 511
Vacuum power assist
The vacuum power assist, made by Ate, consists of a vac-
uum cylinder worked by the brake pedal. This cylinder
is connected by a hose to the engine inlet manifold. The
function of the system is described below.
NOTE
The power assist cylinder cannot be disassembled.
Rest position
In the rest position the valve piston and push rod are held
at the right-hand limit of travel in the guide housing by
the return spring. In this position the atmospheric channef
is closed and the vacuum channel is open.
The same vacuum prevails on both sides of the diaphragm.
VACUUM POWER ASSIST, AT REST
Braking action
When pressing the brake pedal, the valve piston is moved
to the left, the vacuum channel is closed and air ot atmo-
spheric pressure flowes in on the right hand side of the
diaphragm.
The power boost is derived from the difference between
vacuum on the left-hand side of the diaphragm and atmo-
spheric pressure on the right-hand side. The brakes can be
applied harder by heavier pressure on the pedal. When the
driver's foot is removed from the pedal, the spring returns
the valve piston to the rest position, the vacuum channel
opens and the atmospheric channel closes.
If the auxiliary vacuum system should fail, the driving
brakes still work but without the power assist effect. The
power cylinder is then simply an extension of push rod;
the only difference is that heavier pedal pressure is needed
to stop the car.
VACUUM POWER ASSIST, BRAKING
Dec, 1975 SAAB 500-5
Page 512
BRAKE DISCS
Changing brake discs
When a brake disc shows signs of heavy wear after long
mileage it must be exchanged for a new one. Moderately
deep scoring, on the other hand, does not mean that the
disc need be discarded. To change a disc, proceed as fol-
lows:
1. Remove the hub cap and slacken the wheel nuts.
2. Jack up the front end of the car, and remove the wheel
nuts and wheel.
3. Undo the two screws holding the brake housing to the
steering knuckle housing. These screws are accessible
from inside the steering knuckle housing.
4. Lift the brake housing away from the steering knuckle
housing but do not disconnect the brake hose. Be care-
ful not to scratch the brake pistons. Hang up the brake
housing to avoid damage to the brake hose.
BRAKE HOUSING HUNG ON STEEL WIRE
5. Ona front wheel, the parking brake shoes must be
released by means of the adjusting screw to clear the
drum.
6. Back off the two disc retaining screws and remove the
disc.
To fit the new disc, proceed in the reverse order. When
installing the brake housing bolts a new locking plate
should be used.
NOTE
Because of the “disc throw compensators” the brake
pistons must be pushed well back before the brake
housing is mounted on the disc and steering knuckle
housing.
NOTE
After fitting the disc, remember to pump the brake
pedal repeatedly to move the pistons close to the
disc.
Grinding of brake disc
A maximum grinding of 0.02 in. (0.5 mm) on each side
of the brake disc is allowed.
Measuring the brake disc throw
The brake disc throw can be measured with the mea-
suring device 899535 provided with a dial indicator
784062 as follows:
1. Remove the brake pads.
2. Fit the measuring device to the brake pad locking
pins in the brake housing.
3. Fit the dial indicator to the measuring device and
connect the bent measuring point of the tool to the
dial indicator.
4. Rotate the brake disc and read the brake disc throw.
Maximum allowed throw 0,008 in (0.20 mm).
MEASURING THE BRAKE DISC THROW
Tools 784062 and 899535
Dec. 1975
Page 513
BRAKE PADS
General
Because the disc brakes are self-adjusting, it is not possible
to judge by the pedal stroke whether the brake linings are
worn. It is therefore most important to take off the front
wheels at the intervals stated in the service programme and
check the thickness of the linings. The brake pads must be
exchanged when the thickness of the lining is less than
0.08 in. (2 mm).
Changing brake pads
1. Jack up the front or rear end of the car and removed
the wheels.
When the brake pads are worn to the limit and need
changing, they give warning in the form of stiffer pedal
resistance and reduced braking effect. This prior warning
comes from the retaining spring, which is about 0.2”
(5 mm) wider than the disc. When the pads are worn, the
pressure plate of the pad (3) touches the edge of the
spring (5) and the braking effect is reduced.
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$1730
WARNING DEVICE FOR BRAKE PAD WEAR
Brake lining
Brake housing
Pressure plate
Brake disc
Retaining spring
VPon>
Jan. 1972
REMOVING THE GUARD PLATE
DRIVING OUT THE LOCKING PINS
w
. Remove the guard plate and locking pins with a drift.
Remove the pad retaining spring.
. Pull out the pads.
. Damaged dust seals must be exchanged. If dirt has pen-
etrated the brake must be reconditioned.
Page 514
6. Wash the brake disc thoroughly with trichlorethylene.
7. Check that the brake pistons are correct fitted. As
gauge, use tool 899534. Move the tool into the brake
housing with its back against the direction of rotation.
The chamferings of the pistons shall then coincide
with the tool. See fig. If the position of the pistons
is not correct, turn them with pliers 899536.
NOTE
On the rear wheel brakes a washer is placed between
the brake piston and the pad. The washer has a re-
cess and prevents the piston from turning.
8. Fit the brake pads, and make sure that they fit easily
into the recess in the brake housing.
9. Fit the spring, locking pins and guard plate.
10. Pump the brake pedal repeatedly to bring the pads ’
forward to the brake disc.
REMOVING THE RETAINING SPRING 11. Top up the container with brake fluid.
5. Push the pistons back into the cylinder using tool
786043. CAUTION \
Do not forget to pump the brake pedal. Otherwise
it will hit the floor without effect when the brakes
are used.
Removing stucked brake pads
To remove stucked brake pads, use removing tool 899577.
nue > ie INTO THE CYLINDER” sal
Tool 786043 »
NOTE y wD
When the brake pistons are pushed back into the
cylinders, the level in the fluid container will rise.
It may be necessary to drain off some of the fluid.
REMOVING BRAKE PAD
Tool 899577
CHECKING BRAKE PISTON POSITIONS
Tool 899534
Wheel rotation when driving forward
517-2 SADE Dec, 1975
Page 515
HYDRAULIC FOOTBRAKE SYSTEM
Instructions for overhaul
Scrupulous cleanliness is essential when the brake system
or any part of it is disassembled. Wash off dirt and grease
before disassembling. Do not wash any disassembled part
in gasoline, kerosene, trichloroethylene or similar fluid,
as these solvents attack rubber components. Disassemble
units on a workbench covered with clean paper, and
make sure that your hands are clean. After disassembling,
soak all metal parts in a bowl containing clean brake fluid.
Then wipe them with a clean lint-free rag and lay them
out in order on a clean sheet of paper. To insure complete-
ly reliable brake functioning, all rubber parts should be ex-
changed; these are available in complete repair kits. Major
components such as the brake housings should be cleaned
in industrial methylated spirit or brake fluid. If spirit is
used, all traces must be dried off before the brakes are re-
assembled. All component parts are to be dipped in re-
commended brake fluid. See statements in section 020.
Brake fluid
The brake fluid container must be kept well filled at all
times. The level should be checked every 6,000 miles
(10,000 km) or every three months. It is most important
to use the proper quality of brake fluid. Inferior fluids
can totally ruin the hydraulic system. They may for ex-
ample have a low boiling point so that they vaporize
when the brakes are applied hard. This puts the brakes
out of action, possible with disastrous results.
Even the best brake fluids deteriorate with time through’
oxidation and water absorption, which lowers the boiling
point. For this reason the brake fluid should be changed
once a year if the car is used for competition or alpine
driving.
Normally, brake fluid should be changed when the brake
system is reconditioned, i.e. every other year or 24,000
miles (40.000 km). Brake fluid must always be stored in
a sealed container. Use only recommended brake fluid.
See statements in section 020.
Changing brake fluid
1. Open the bleeder screws on the primary circuit (right
front and left rear wheel) and connect hoses as when
bleeding. Pump the brake pedal until the fluid con-
tainer is nearly empty. Then fill with fresh fluid and
continue to pump until the system is completely filled
with fresh fluid. Tighten the bleeder screws. Then
repeat the operation for the secondary circuit, (left
front and right rear wheel). Pump through at least half
a quart (half a liter). Top off the container.
2. Bleed the brake system.
Dec, 1975
Bleeding the brake system
\f air has entered the system, this can be detected by
sponginess in the brake pedal or the need to press the
pedal several times before the brakes take hold.
Each wheel has a bleeder screw located in the inner part
of the brake housing. It is easier to bleed the system if
the car is first blocked up. The best result is achieved with
a bleeding equipment, and the maker’s instructions should
be followed,
The following method can also be used:
1. Make sure that the brake fluid container is well filled
and the vent holes in the cap are not blocked,
2. Bleed either one wheel at the time or two wheels at
the same time. Connect suitable hoses to the bleeder
screws.
3. Place the free ends of the hoses in a container part-filled
with clean brake fluid.
4. Open the screws 1/2—1 turn.
= $1736
BLEEDING THE BRAKE SYSTEM
- Bleedev mugplor Taam
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SAAB 520-1
Page 516
5. Have a helper pump the brake pedal in easy time until
the outflowing fluid is free from air bubbles. The ends
of the hoses must be kept below the liquid surface in
the glass container at all times.
6. Close the bleeder screws with the brake pedal held down.
7. Check that the brake fluid container does not run empty
during bleeding.
8. Top off the container with fresh fluid after bleeding
both circuits.
LOCATION OF BLEEDER NIPPLE
Dec. 1975
Page 517
Ld
—4, Undo the clip that holds the speedometer cable to HD
~—5. Undo the vacuum hose connection.__—
—6. Disconnect the push rod from the brake pedal.
7. Undo the four screws that hold the power assist unit
MASTER CYLINDER
General
All rubber gaskets and seals in the brake system should be
changed at intervals of not more than three years or 35,000
miles (60,000 km). Scrupulous cleanliness is essential when
the brake system or any part of it is disassembled Wee also
section 520).
Overhaul
The master cylinder should not be disassembled unless
there is no replacement cylinder available.
Removing the master cylinder with vacuum power assist
—1., Lay protective over the front fender and lay rags under
the master cylinder to avoid damage to paintwork in
case brake fluid should be spilt.
Remove the air cleaner.
3. Undo the brake line connections and put plastic stoppers
in the holes.
power assist unit.
to the dash panel and lift off the unit.
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Disassembly
1. Separate the power assist unit from the master cylinder
by backing off the nuts from the two retaining bolts.
-2. Remove the lock ring (10) that holds the primary pis-
ton (12) in place.
. Back off the stop screw (13).
4. Pull out the primary piston (12) with spring (5) and
the secondary piston (4) with spring (5) and seals.
5. To change the seal ring (6) on the primary piston, the
screw (9) with spring must be completely unscrewed
and the spring retainer, support ring and support wash-
er removed to gain access to the seal ring.
Inspection
1. Check that the cylinder bore is not scratched.
2. Check that the through-flow holes are clear by testing
with a fine iron wire.
3. Check all parts and exchange any that are worn or
defective.
Rubber gaskets and seals should be replaced by new ones.
Repair kits containing complete replacement sets of rubber
gaskets and seals are available.
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oO MASTER CYLINDER
od 1. Container 8. Sleeve
2. Rubber seal 9. Screw
3. Housing 10. Lock ring
4. Secondary piston 11. Seal ring
5. Spring 12. Primary piston
6. Piston seals 13. Screw
7. Washer
521-1
Jan. 1971
Page 518
Assembling -- fitting Removing the master cylinder
(Dip all parts in brake fluid before assembling.) 1. Lay protective over the front fender and lay rags under
the master cylinder to avoid damage to paintwork in
~1. Insert the secondary piston (4) with spring and seals. case brake fluid should be spilt.
~2. Insert the primary piston (12) with spring and seals. 2. Unscrew the brake line unions from the master cylinder,
“3. Fit the lock ring (10). plugging the cylinder openings with plastic stoppers as
—4. Bolt the master cylinder to the power assist unit. each line is disconnected.
™5. Cover all openings to keep dirt out of the cylinder 3. Back off the two retaining nuts and lift the master
during installation. cylinder off the power assist unit. Empty the cylinder
~6.._ Fit the master cylinder complete with power assist of brake fluid.
unit to the dash panel and connect the push rod to
the brake pedal.
~7. Connect the brake lines.
8. Connect the vacuum hose and the clip that holds Fitting
the speedometer cable to the power assist unit.
9. Mount the air cleaner. 1. Cover all openings to keep dirt out of the cylinder dur-
10. Fill the container with brake fluid and bleed system. ing installation.
2. Mount the cylinder on the two bolts of the power assist
unit and tighten the nuts.
3. Connect the brake lines and fill the cylinder with brake
fluid.
4. Bleed the system (see section 520).
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MASTER CYLINDER
1. Container 8. Sleeve
2. Rubber seal 9. Screw
3. Housing 10. Lock ring
4. Secondary piston 11. Seal ring
5. Spring 12. Primary piston
6. Piston seals 13. Screw
7. Washer
521-2. SAAB April 1969
Page 519
BRAKE LINES
The brake pipers are of 3/16 in. Bundy tube. The ends of
all the pipes are flanged and fitted with compression nuts,
which must be passed onto the pipes before the ends are
flanged. It is important to ensure that the pipes are prop-
erly flanged so that there will be no leakage at the joints.
See fig. For reasons of safety, it is essential that all pipes,
rubber hoses and connections in the brake system be kept
in first-class condition at all times. Bearing this in mind,
check regularly that the hoses have not been damaged by
flying stones or by abraison. Pipes, too, must be installed
so that they cannot rub or chafe against anything.
Make sure that the pipes and handbrake cables on the in-
clined panel under the rear seat are correctly fitted, so
that they cannot rub against each other and so that the
pipes cannot get damaged by the seat cushions.
All pipe and hose connections must be properly tighte-
ned to ensure leak-free joint. Make sure that the copper
gaskets in the pipe connections are flawless, and change
any defective ones. Copper gaskets which have become
so hard that they no longer seal effectively may, however,
be annealed and reused.
Pipes which are to be installed must fit well at both ends
and at the clips. Never stretch a badly-fitting pipe by
means of the compression nuts or bend an already fitted
pipe. Both of these courses could give rise to stresses
which may result in leakage, pipe fracture or stripped
threads.
Pipes for connection to brake hoses are flanged as per
“type A’. Other pipes are flanged as per “type B”.
Nov. 1969
A B
FLANGING OF BUNDY TUBING
Brake hoses
The brake system incorporates two front and two rear
brake hoses, affording the communication between the
body and the wheel cylinders. These hoses are of diffe-
rent lengths and must not be confused. Install the hoses
with the wheels freely suspended and aligned straight
ahead. When tightening the brake pipe, hold the brake-
hose nipple (not the locking nut) to prevent the hose
from twisting and changing position.
WARNING
When fitting brake hoses it is highly important to
position them correctly, thereby ensuring that
steering or suspension movements do not bring
them into contact with other parts of the car. The
brake hoses must not be wrung or twisted but shall
be mounted in a neutral position. In addition, see to
it that the front hoses form a downward directed
curve.
Page 520
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