Buick LeSabre 1965 Service Manual page 534

9 - 1 2 TROUBLE DIAGNOSIS
BRAKES
(c) Blocked Air Inlet. Check con-
dition of air cleaner. Clean or
replace parts as required.
(d) Air Valve Sticking in Power
Piston. Remove and disassemble
p o w e r cylinder for inspection
(par. 9-16).
(3) If above test shows that power
cylinder is operating but not giv-
ing normal brake action, check
the following items.
(a) Insufficient Brake Fluid in
System. Fill reservoir, bleed all
lines and check for leaks (par.
9-6).
(b) B r a k e Lining C o n d i t i o n .
Check for glazed, dirty, or oily
brake linings. Clean or replace.
g. Brakes Drag at One Wheel
(1) Loose Front Wheel Bearings.
Check for play in bearings with
wheel jacked up and adjust if
necessary (Group 7).
(2) Insufficient C l e a r a n c e at
Brake Shoes.
(3) Weak or Broken Brake Shoe
Spring. Replace spring and check
brake shoe adjustment (par. 9-10).
(4) Wheel Cylinder Piston Stuck
or Cups Distorted. May be caused
by dirt in hydraulic fluid, impro-
per fluid, or previous use of a
cleaning fluid which is detrimental
to rubber parts. Overhaul wheel
cylinder and replace any defective
parts (par. 9-12). It is also ad-
visable to flush hydraulic system
to prevent repetition of trouble
(par. 9-6).
(5) Obstruction in Brake Pipes
or Hoses. Obstruction may be
caused by foreign material, dam-
aged pipe, kinked or deteriorated
brake hose. Flush hydraulic sys-
tem (par. 9-6) or replace dam-
aged or defective part as required.
h. Brakes Drag at All Wheels
(1) Insufficient C l e a r a n c e at
Brake Shoes.
(2) Master Cylinder Piston Com-
pensating Holes Closed. If the
compensating holes are plugged
by foreign material, or are cov-
ered by the piston primary cup
when brake pedal is in released
position, high pressure will be
maintained in hydraulic system
and brake shoes will be held in
contact with drums. This condi-
tion is indicated by lack of normal
pedal travel and a very solid feel
when pedal is depressed.
Make certain that pedal is free on
pivot and at push rod connection.
If freeing up brake pedal does not
correct the trouble, remove mas-
ter cylinder for disassembly and
thorough cleaning (par. 9-13).
CAUTION: Never insert a test
wire through compensating holes
as this may leave a burr, which
will cut a groove in primary cup.
(3) Wheel Cylinder Piston Cups
Distorted. If the rubber parts in
master cylinder are found to be
swollen and distorted (Step 2,
above), it indicates the presence
in hydraulic system of a mineral
base oil such as kerosene, gaso-
line, or engine oil. Such sub-
stances will cause all rubber
parts to swell and distort; there-
fore it is necessary to thoroughly
flush the hydraulic system (par.
9-6) and replace all rubber parts.
i. Power Brakes Do Not
Release Properly
Refer to subparagraph h above for
causes of brake drag due to condi-
tions other than the power brake
cylinder and its control linkage.
(1) Binding Push Rod. See sub-
paragraph e, item (1).
(2) Swollen Hydraulic Cups. See
subparagraph e item (2).
(3) Plugged Compensating Ports.
Remove and disassemble power
cylinder, clean thoroughly (par.
9-17), also flush brake hydraulic
system to remove all dirt.
(4) Power Unit Internal Friction.
Remove, disassemble and inspect
power cylinder, looking particu-
larly for weak or broken springs
and for dry rubber cups and "O"
ring seals. Reassemble as speci-
fied (par. 9-16).
j . Car Pull to One Side
(1) Tires Unequal. T i r e s un-
equally inflated, or having unequal
wear of treads or different non-
skid tread designs may cause car
to pull to one side when brakes
are applied. Inflate all tires to
specified pressure (par. 1-1).
Rearrange tires if necessary so
that tread non-skid characteris-
tics are more nearly equal on
both sides of car.
(2) Brake Shoes Improperly Set.
Although hydraulic brakes a r e
self-equalizing so far as applying
pressure at each brake shoe is
concerned, the brake shoes will
not hold equally if not centered
in drums, or if the wear pattern
is not uniform on all four shoes.
(3) Loose Front Wheel Bearings.
Check for play in bearings with
wheels jacked up and adjust if
necessary (Group 7).
(4) Out-of-Round or Scored Brake
Drums. True up or replace as
required (par. 9-11).
(5) Brake Linings Not Matched,
or Improperly Placed. Brake lin-
ings must be of same composition
on left and right sides of car,
otherwise unequal braking action
will result. If primary and sec-
ondary linings are interchanged
at any wheel, unequal braking will
be obtained. Replace or change
linings as required (par. 9-10)'
(6) Foreign Substances on Some
Brake Linings. Any foreign sub-
stance on linings will affect brak-
ing action. Thoroughly clean any
linings having water, sand, paint,