Chevrolet 1980 Light Duty Truck Service Manual page 358

5-4 BRAKES
vehicle stopped and pedal pushed near fully depressed
position.
3. Whenever the accumulator pressure is used, a slight
hiss may be noticed. It is the sound of the hydraulic fluid
escaping through the accumulator valve, and is completely
normal.
4. After the accumulator has been emptied, and the
engine is started again, another hissing sound may be heard
during the first brake application or the first steering
maneuver. This is caused by the fluid rushing through the
accumulator charging orifice. It is normal and will only be
heard once after the accumulator is emptied. However, if
this sound continues, even though no apparent accumulator
pressure assist was made, it could be an indication that the
accumulator is not holding pressure and should be checked
using the procedure
LEAKDOWN TEST".
5. After bleeding, a "gulping" sound may be present
during brake applications as noted in the bleeding
instructions.
CHECKING THE RESERVE SYSTEM
1. Start engine and charge accumulator by applying
the brake pedal or by turning the steering wheel from stop
to stop. Turn off engine and let vehicle sit for one hour.
After one hour there should be at least two power assisted
applications with the engine off.
for "ACCUMULATOR
2. If the reserve system will not retain a charge for one
hour, but functions normally immediately following
charging, the accumulator valves are at fault and the booster
must be disassembled and the accumulator valves replaced.
3. If the accumulator can be heard charging and
discharging, but it does not hold a charge, disassemble the
booster and replace the accumulator valves.
4. Deplete the accumulator by pressing the brake
pedal 4 or 5 times. If the accumulator can has lost its gas
charge, it is possible to rotate or wobble the accumulator
can with respect to the housing. Replace the accumulator
assembly.
BOOSTER FUNCTIONAL TEST
With the engine off, apply the brake pedal several times
until the accumulator is completely depleted. Depress the
brake pedal (approximately 40 pounds/180 N pedal force)
and start the engine. The pedal should fall and then push
back against driver's foot.
ACCUMULATOR LEAKDOWN TEST
Start engine and charge accumulator by either applying
the brake pedal (approximately 100 pounds/450 N force)
or by turning the steering wheel from stop to stop. Turn off
engine and let vehicle sit for one hour. After one hour there
should be two power assisted applies with engine stopped.
LIG H T T R U C K S ER V IC E M ANUAL