Cadillac 54-6219 1954 Shop Manual page 165

9-20
BRAKES
DIAGNOSIS CHART Cont'd
Power Brake Cont'd.
EFFECT CAUSE REMEDY
Hissing noise, engine running,
brakes on only.
Internal vacuum leak
-
air en-
ters through breather,
Overhaul unit, and check for
leak at vacuum poppet, con
trol diaphragm, or vacuum
power piston.
Little or no
boost
from power
brake. May be accompanied by
hissing noise or loss of brake
fluid,
Internal vacuum leak between
atmospheric and vacuum side
of vacuum power piston,
Internal hydraulic leak.
External hydraulic leak.
internal friction.
Overhaul unit, and check for
leak at vacuum poppet, control
diaphragm, or vacuum
power
piston.
Check for low brake fluid level.
Overhaul unit, and check for
presence of brake fluid in inner
side of vacuum cylinder, or in
ner side of control diaphragm.
Check
and correct leaks at
control valve cup, control valve
fitting "0" ring seal,
vacuum
piston push rod seals, or hy
draulic power piston cup or ball-
check.
Correct leak at point of origin.
Check and correct Shock Ab
sorber Fluid level in vacuum
cylinder. If
necessary, overhaul
unit, and check for rusty, dirty,
or distorted vacuum cylinder
wall, dry or worn vacuum pis
ton leather packing, swollen
rubber cups due to heat or wrong
brake fluid, worn or damaged
rubber cups, or
dirt, rust,
sludge, or foreign matter in
power piston or control valve
regions.
Booster loses effectiveness
while stopping. Pedal grows
harder, or "kicks back",
Internal hydraulic leak.
Internal
or external vacuum
leak,
Overhaul unit, and check for
small leaks at control valve,
valve fitting, and power piston.
Overhaul unit, and check for
leak at vacuum poppet, control
diaphragm, or vacuum power
piston.
Tendency to over-brake, pedal Restriction in atmospheric
pas- Clean air filter.
drops under
foot. May show up sage.
as slow application of Power
Brake.
Sticky control valve. Overhaul unit, and check for
misalignment of control valve
assembly.
Check for
dirty or sticky vac
uum or atmospheric poppet, as
well as sticky control valve.