Pontiac tempest 1968 Service Manual page 176

S T A N D A R D BRAKES 5-11
Air may also enter the system occasionally when
brake shoes are replaced. This air must be re­
moved by bleeding.
Bleeding may either be done by hand pumping the
brake pedal using bleeder tube as outlined below or
by using pressure bleeding equipment.
CA UTION: Always clear away any dirt around
master cylinder reservoir cover before removing
cover for any reason. Never depress pedal while
brake drums are removed unless bleeder valve is
open.
When using pressure bleeding equipment follow in­
structions of the equipment manufacturer and always
use bleeder tube attached to wheel cylinder to prevent
brake fluid from running inside the brake assembly
and ultimately on the brake linings.
When bleeding by operating pedal proceed as out­
lined below:
1. F i l l master cylinder reservoir with recom­
mended brake fluid.
CA UTION: Never use an inferior or reclaimed
brake fluid as this will positively result in brake
trouble. Even though reclaimed fluid may look
clear, tests have shown such fluid to be corrosive.
If there is doubt as to the grade of fluid in the sys­
tem, flush out system and fill with recommended
brake fluid complying with SAE 70-R-3 specifica­
tions such as Delco Supreme 11.
2. On models equipped with master cylinder
bleeder screws (Tempest and Firebird Power Brake
units), bleed master cylinder by following procedure.
Attach bleeder tube to valve and allow tube to hang
submerged in brake fluid in a clean quart glass j a r .
Using brake bleeder wrench or equivalent, unscrew
bleeder valve three quarters of a turn. Depress
pedal full stroke and allow it to return slowly making
sure end of bleeder tube is under surface of liquid in
container. Continue operating pedal, refilling res­
ervoir after each five strokes (unless an automatic
filling device is used), until liquid containing no air
bubbles emerges from bleeder tube.
3. Close bleeder valve assembly and bleed other
master cylinder bleeder valve.
NOTE: If a power brake unit has been installed on
a Tempest or Firebird and the original manual
master cylinder (without bleeder valves) is used,
these units may be bled by unscrewing the master
cylinder brake line three-quarters of a turn, de­
pressing brake pedal, tightening brake line, then
releasing brake pedal
4. After master cylinder has been bled wheel cyl­
inders may be bled in the following order using the
above procedure: left front, right front, left rear
and right rear.
B O O T
/ P I S T O N
/ P I S T O N C U P
/ C U P RETURN S P R I N G
W i r H E X P A N D E R S
t -' / WHEEL CYLINDER
4 s K
H O U S I N G
• . . /
P I S T O N C U P
, ; f / PISTON
i- '
/ B O O T
/ /
BLEEDER S C R E W
Fig. 5-12 Wheel Cylinder — Exploded View
CA UTION: Bleeder tube should always be used
when bleeding brakes, and end of tube must be be­
low level of brake fluid in glass jar when bleeding
other than by pressure.
5. When bleeding operation is completed, refill
reservoir as shown in Fig. 5-6, then replace res­
ervoir cover.
FLUSH HYDRAULIC SYSTEM
It may sometimes become necessary to flush out
the brake hydraulic system due to the presence of
mineral oil, kerosene, gasoline, carbon tetrachlo­
ride, etc., which will cause swelling and/or deteri­
oration of rubber piston cups and valves so they
become inoperative.
NOTE: If it becomes necessary to replace brake
fluid lines, use only steel lines with double-flared
ends.
To flush hydraulic system proceed as follows:
1. Attach bleeder tube and open bleeder valve at
left front wheel.
2. Flush out system thoroughly with clean dena­
tured alcohol, pumping the fluid from master cylin­
der reservoir and out of wheel cylinder bleeder
valve.
3. Repeat steps 1 and 2 at remaining wheel cylin­
ders. To ensure thorough flushing, approximately
1/2 pint of alcohol should be bled through each wheel
cylinder.
4. Replace all rubber parts in master and wheel
cylinders. Thoroughly clean cylinders and pistons in
alcohol before installing new parts.
5. After installing parts, fill system with recom­
mended brake fluid and follow steps 2 through 4 un­
der B L E E D I N G BRAKES to flush system of cleaning