1987 SUZUKI GRAND VITARA Service Repair Manual

DRUM BRAKE ASSEMBLY (Rear Wheel Brake)
[GENERAL DESCRIPTION]
The drum brake assembly has a self shoe clearance adjusting system so that drum-to-shoe clearance is
maintained appropriate at all times. For details, refer to OPERATION in the next page.
NOTE:
Replace all components included in repair kits used to service this drum brake. Lubricate parts as specified.
WARNING:
When servicing wheel brake parts, do not create dust by grinding or sanding brake linings or by clean-
ing wheel brake parts with a dry brush or with compressed air. (A water dampened cloth should be
used.) Many wheel brake parts contain asbestos fibers which can become airborne if dust is created
during servicing Breathing dust containing asbestos fibers may cause serious bodily harm. If any
hydraulic component is removed or brake line disconnected, bleed the brake system. The torque
values specified are for dry, unlubricated fasteners.
1. Brake back plate
2. Brake shoe
3. Shoe return spring (A)4. Brake strut rod
5. Shoe return spring (B)
6. Rod spring7. Shoe hold down spring
8. Shoe hold down pin
9. Wheel cylinder10. Stopper plateiI7
Fig. 19-8
19-8

[Rear brake OPERATION]
With the general drum brake type, when the
brake pedal is depressed, two pistons in the
wheel cylinder force the brake shoes outward,
restraining the turn of the drum.
The more the brake shoes get worn, the longer
distance the pistons must move. As a result, the
brake pedal travel (pedal-to-wall clearance)
increases. Then the shoe clearance must be
adjusted by the shoe adjusting screws. Thus
periodical adjustment is required for the drum
brake type in general.
This rear brake is provided with a self-adjusting
system which automatically adjusts the shoe-to-
drum clearance (pedal-to-wall clearance) caused
by such brake shoe wear.
Clearance correction
In each rear wheel cylinder, pistons, piston cups,
and a piston spring (1) are installed. When the
brake pedal is depressed, fluid pressure is applied
to the inside of the chamber on the piston (2),
(3).
Being actuated by this pressure, the piston (2)
moves to the left (piston (3) moves to the right)
in the following figure and presses the brake
shoe against the brake drum, thus producing
brake force.
(2)(3)
Fig. 19-9
At this time, the distance the brake shoe moves
is “B”,that is, the distance that “A” (the end of
the long hole made in the brake shoes web)
moves till it contacts the lever (1) which is fitted
in the long hole.
Fig. 19-10
When the brake pedal is depressed, the piston
and brake shoe move toward the brake drum
side by the aforementioned distance “B” and
“A” of the brake shoe web contacts the lever
(1). As the brake shoe gets worn and the brake
shoe clearance becomes larger, the force applied
to the lever (1) at the time of such a contact
becomes larger. When it exceeds 10 - 12 kg
(22 - 26 Ibs), the “A” of the brake shoe web
moves the lever (1) as much as the amount of
the brake shoe lining wear toward the direction
as shown with an arrow in the figure. Thus the
shoe is forced against the drum and the brake
force is produced.
19-9

The distance the lever (1) moves corresponds to
the amount of wear. In accordance with the
lever (1) movement, the fan-shaped ratchet (2)
also moves, for they are assembled as a unit. The
lever (1) and ratchet (2) remain in the positions
as they moved until the shoe-to-drum clearance
becomes even larger.
When the brake pedal is released, the brake shoe
is allowed to move back by the amount of
clearance “B” by means of the return spring. In
this way, the brake shoe-to-drum clearance is
automatically adjusted constant every time the
brake pedal is depressed.
The brake shoe-to-drum clearance “B” corre-
sponds to 0.6 - 0.8 mm (0.0236 - 0.0315 in.)
in terms of the brake drum diameter A tf A’.
And the amount adjusted by one notch of the
ratchet corresponds to 0.20 mm (0.008 in.) in
terms of the brake drum diameter A - A’.
The spring provided in the wheel cylinder
prevents the piston from moving back more than
the specified brake shoe-to-drum clearance.
Fig. 19-11
19-10

BOOSTER ASSEMBLY
[GENERAL DESCRIPTION]
The booster is located between the master cylinder and the brake pedal. It is so designed that the force
created when the brake pedal is depressed is mechanically increased combined with the engine vacuum.
The booster has a diaphragm of 4 180 mm effective diameter. Its operation is described in the following pages.
NOTE:
Use all components included in repair kits to service this booster. Lubricate rubber parts, where indicat-
ed, with silicone grease provided in kits. The torque values specified are for dry, unlubricated fasteners.
If any hydraulic component is removed or brake line disconnected, bleed the brake system.
Never lubricate any hydraulic component with silicone grease.
11.Vacuum check valve11.No. 2 body oil seal
2.3.Grommet12.Booster air valve assembly
Booster No. 1 body13.Air cleanerseparator
4. PistonRod14.Air cleaner element
5. Reaction disc 15.Body boot
6.Booster piston returnspring16.Nut7. Valve stopper key17.Bracket
8.Booster piston18.Push rod clevis
9. Diaphragm19.Pressure plate
10.Booster No. 2 body
Fig. 19-12
19-11

[Booster OPERATION]
1.BoosterNo. 1 body2.BoosterNo. 2 body3. Valve operating rod4. Air cleaner element
5. Air cleaner separator6. Air valve spring retainer7. Air valve return spring 8. Control valve spring retainer
9. Control valve spring
10. Booster control valve
11. Booster air valve
12.
13.Boosterpiston Valve stopper key 14.Boosterdiaphragm15. Reaction disc16. Booster piston return spring17. Booster piston rod18. Booster rod adjust screw19. Vacuum check valve
Fig. 19-13-1 Vacuum Booster Assembly
When the brake pedal is depressed, the force is transmitted to the piston of the master cylinder through
the valve operating rod, booster air valve, reaction disc and piston rod. At the same time, the force of the
booster piston developed due to the pressure difference between the two chambers “A” and “B” in the
above figure is added to it.
The end of the booster control valve has a double function of a vacuum valve and air valve. That is, as
shown in the figure, the booster control valve closes between the “A” and “B” chambers as its outer end
“C” contacts the booster piston seat and opens as“C” leaves the booster piston seat (vacuum valve
function). Also it closes between the “B” chamber and outside air as its inner end “D” contacts the air
valve seat and opens as “D” leaves the air valve seat (air valve function).
When foot brake pedal is not depressed
The valve operating rod is pushed to the right by the spring force as shown. The air valve is also enough to
the right to contact the valve stopper key as shown. In this state, the vacuum valve (control valve “C”) is
open and the air valve (control valve“D”) is closed. Thus the chambers “A” and “B” conduct and share
the same negative pressure (because of no pressure difference) which allows the return spring to push the
booster piston to the right.
II--1
Vacuum valve “C”---
-d&
tAir valve “D”
Control valve
Nl1. Booster control valve
I“B”2. Booster air valve
3. Booster piston
Fig. 19-13-2 Vacuum Booster Assembly
19-12

When foot brake pedal is depressed
Being pushed by the operating rod, the booster
air valve moves to the left as shown. Then the
control valve is pushed against the booster
piston seat closely by the valve spring force.
Thus the vacuum valve (control valve “Cl’)
is closed to cut off between the chambers “A”
and “B”. At this time the air valve (control valve
“D”) is still closed.
Booster control valve
2.Booster air valve
3. Booster piston
Fig. 19-14-1
As the booster air valve moves further to the
left, it leaves the control valve and the air valve
(control valve “D”) opens to allow the air to
flow into the chamber “B”. The entry of air
causes a difference in pressures between the
chambers “A” and “B” When this pressure
difference grows greater than the piston return
spring force, the booster piston moves to the left
and the booster control valve also moves to the
left. The resulting air valve (control valve “D”)
closure stops the air flow into the chamber “B”
and its pressure remains as it is. In this way, a
small brake pedal depressing force is made into
a strong push to the master cylinder push rod to
produce high hydraulic pressure.
Vacuum valve “C”I
Control valve
1. Booster control valve2. Booster air valve
3. Booster piston
Fig. 19-14-2
When foot brake pedal is released
When the brake pedal is released, the booster air
valve returns to the right by the master cylinder
piston return force and the air valve return
spring force as shown. Then the vacuum valve
(control valve “C”) opens and causes negative
pressure in the chamber “B”. The result is that
the master cylinder piston and booster piston
return to their original positions. This is the
same state as described under “When foot brake
pedal is not depressed”.
Fig. 19-14-3
2.Air valve return spring
3. Booster piston4. Booster control valve
Reference
Should any of the vacuum related parts in the
booster be faulty, the brake force is not increas-
ed. Even then, however, the brake depressing
force is transmitted to the valve operating rod,
booster air valve, valve stopper key and booster
piston in that order, to push the master cylinder
push rod. Thus, the braking operation itself will
Fig. 19-14-419-13

19-2. FRONT DISC BRAKE4) Remove caliper (cylinder).
REMOVAL
1) Loosen, but do not remove, front wheel nuts.
2) Hoist car.
3) Remove wheel nuts and take off front wheels.
Brake Pad
After taking down the wheel, remove brake
pads according to the following procedure.
1) Remove caliper antirattle clip.
Fig. 19-17
2) Remove caliper guide pin caps (2 pcs).
3) Remove caliper guide pins (2 pcs) by using 6
mm hexagon wrench.
NOTE:
During removal, be careful not to damage brake
flexible hose.
Also, don’t depress brake pedal.
5) Remove pads.
Fig. 19-20
Fig. 19-18
19-14

Caliper
After taking down the wheel, remove piston and
piston seal according to the following procedure,
1) Clean outside of reservoir.
2) Take out fluid with a syringe or such.
3)Wipe caliper clean.
4) Disconnect brake flexible hose from caliper
body (cylinder).
Fig. 19-21
6) Blow compressed air into cylinder through
bolt hole where flexible hose was fitted. With
this air pressure, the piston can be pushed out
of cylinder.
WARNING:
Do not apply too highly compressed air
which will cause piston to jump out of
cylinder. It should be taken out gradually
with moderately compressed air. Do not
place your fingers in front of the piston
when using compressed air to push it out
Fig. 19-23
5) Remove caliper (cylinder) and bolt. For
removal of caliper and pads, refer to steps 1)
through 5) of brake pad removal in this
section (p. 19-14).
Fig. 19-22
7) Remove piston seal using a thin blade like a
thickness gauge, etc.
CAUTION:
Be careful not to damage inside (bore side)
of cylinder.1
Fig. 19-24
19-15