GMC 1982 Light Duty Truck, Service Manual

Page: 544 / 1435

5-24 BRAKES
7. Install the rod up through the floorpan opening and
install the lower pivot bolt, special washers and nut.
Tighten the nut to 22-30 lb. ft. (30-40 N-m) and install
a NEW cotter pin.
8. Push the boot up to the floorpan.
9. Lower the vehicle from the hoist.
10. Install the rod upper pivot bolt, special washers and
nut. Tighten the nut to 22-30 lb. ft. (30-40 N-m) and
install a NEW cotter pin.
11. Fasten the boot to the floorpan and compress the boot,to
2.54" (65 mm) installed height; tighten the boot to
2.54" (65 mm) install height; tighten the boot screws to
13-18 lb. in. (1.5 - 2.0 N-m). (Refer to Figure 5-13).
12. Adjust brake pedal and stoplamp switch as outlined
previously.
P30(42) and G M odels
Replacement
1. G Models- Remove the brake pedal striker screw and
remove the striker. Remove the cotter pin and washer
and disconnect the pedal rod from the brake pedal.
2. P30(42) Models- Remove the cotter pin nut and bolt to
disconnect the pedal rod from the brake pedal.
3. Remove the pedal rod retainer bolt (at the rod pivot)
and remove the retainer.
4. Remove the cotter pin and washer and remove the
pedal rod.
5. To install a new rod, reverse Steps 1-4 above. Lubricate
pivot points with Delco Brake Lube (or equivalent).
NOTICE:
See "Notice" on Page 1 of this section.
6. Check brake pedal and stoplamp switch adjustments as
outlined previously.
MASTER CYLINDER
Filling Cylinder
The master cylinder must be kept properly filled to
insure adequate reserve and to prevent air from entering the
hydraulic system. However, because of expansion due to
heat absorbed from brakes and from engine, master cylinder
must not be overfilled.
The brake fluid reservoir is on the master cylinder
which is located under the hood on the left side of the dash.
Thoroughly clean reservoir cover before removal to
avoid getting dirt into reservoir. Remove cover and
diaphragm. Add fluid as required to bring level to 1/4" (6
mm) (plus or minux 1 /8 " —3 mm) from the lowest portion of
the top of each reservoir. Use Delco Supreme No. 11
Hydraulic Brake Fluid or equivalent.
Do not use shock absorber fluid or any other fluid which
contains mineral oil. Do not use a container which has been
used for mineral oil or a container which is wet from water.
Mineral oil will cause swelling and distortion of rubber parts
in the hydraulic brake system and water will mix with brake
fluid, lowering the fluid boiling point. Keep all fluid
containers capped to prevent water contamination.
Except Bendix M ini-M aster Cylinder and Delco
Quick Take-Up M aster Cylinder
Removal
1. Disconnect brake pipes from master cylinder and tape
end of pipes to prevent entrance of dirt.
2. Manual brake only—Disconnect brake pedal from
master cylinder push rod.
3. Remove two nuts holding master cylinder to dash or
power cylinder and remove master cylinder from
vehicle. Be careful not to drip brake fluid on exterior
paint.
Disassembly (Figs. 5 -14 and 5-15)
1. Clean outside of master cylinder thoroughly. Remove
reservoir cover and diaphragm. Turn cylinder over and
pump push rod by hand to drain all brake fluid. Always
discard used fluid.
2. Manual brake only—Pull boot away from master
cylinder to uncover push rod retainer. The retainer has
a small, depressed tab in the side. This tab must be
pried up to release retainer.
3. Depress piston and remove secondary piston stop bolt
from bottom of front fluid reservoir (if so equipped).
4. Place master cylinder in a vise so that lock ring can be
removed from groove in the inside diameter of bore.
Remove lock ring and primary piston assembly.
Remove secondary piston, secondary piston spring and
retainer by blowing air through the outlet port.
5. Place master cylinder in vise, so that outlet holes are
up. Enlarge hole in tube fitting insert using a 13/64"
drill. Place a heavy washer over outlet on master
cylinder and thread a 1/4-20 x 3/4" screw into the
insert. Tighten screw until insert is unseated. Remove
insert, screw, and washer.
6. Remove primary seal, and secondary seal from
secondary piston.
7. Use clean brake fluid to clean all metal brake parts
thoroughly. Air dry and place cleaned parts on clean
paper or lint free clean cloth.
Do not use anti-freeze alcohol, gasoline, kerosene, or
any other cleaning fluid that might contain even a trace
of mineral oil.
Inspection
Inspect cylinder bore for scoring or corrosion. It is best
to replace a corroded cylinder. Corrosion can be identified as
pits or excessive roughness.
Polish any discolored or stained area with crocus cloth
by revolving cylinder on cloth supported by finger.
Rinse cylinder in clean brake fluid. Shake excess
rinsing fluid from cylinder. Do not use a rag to dry cylinder,
as lint from rag cannot be kept from cylinder bore surfaces.
Make certain that compensating port in cylinder is
clear.
If scratches or corroded spots are too deep to be
polished satisfactorily, the cylinder should be replaced.
Assembly
1. Place brass tube fitting insert (new parts) in outlet
holes so that it is in a position to be pressed into outlet