GMC 1986 P-Truck Service Manual page 423

3. Check and fill the power steering reservior with
power steering fluid. If fluid contains air refer to
POWER STEERING (Sec. 3B3) for further diag­
nosis.
4. Check power steering pump belt for wear and
tension. Adjust if needed, refer to POWER
STEERING (Sec. 3B3).
5. Check engine idle speed, refer to the vehicles
Emission Control Inform ation label for idle
specifications.
6. Check steering pump pressure. Refer to POWER
STEERING (Sec. 3B3).
NOISE DIAGNOSIS
The following noises are associated with the
Hydro-Boost and may or may not be cause for
customer complaint. Some noises are normal and for
the most part temporary in nature. Other noises may
be a sign of excessive wear or the presence of air in
either the booster or the steering system.
1. A m oan or low fre q u e n c y
accompanied by a vibration in the pedal or
steering column may be observed during parking
maneuvers or other low speed maneuvers. This
may be caused by a low fluid level in the power
steering pump or by air in the fluid. Holding the
pump at relief pressure (steering wheel held all
the way in one direction) for more than five
seconds will cause air to enter the system. Check
the fluid level and fill if needed. The system must
then sit for one hour to remove the air. If the
condition persists, refer to POWER STEERING
(Sec. 3B3).
2. A high speed fluid noise may be heard when the
brake pedal is fully depressed, this condition is
normal.
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 for the " Accumulator Leakdown
Test" in this section.
BOOSTER FUNCTIONAL TEST
With the engine off, apply the brake pedal several
times until the accumulator is completely depleted.
Depress the brake pedal using 180 N (40 lbs.) of force
and start the engine. The pedal will fall and then push
back against your foot.
hum u s u a lly
ACCUMULATOR LEAKDOWN TEST
1. Start the engine and charge the accumulator by
2. If the reserve system will not retain a charge for
3. If the accumulator can be heard charging and
4. Deplete the accumulator by pressing the brake
SEAL LEAK DIAGNOSIS (FIGURE 1)
A. INPUT ROD SEAL. A damaged seal will show up
applying the brake pedal or by turning the
steering wheel from stop to stop. Turn off the
engine and let the vehcile sit for one hour. After
one hour there should be at least two power
assisted applications with the engine off.
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.
discharging, but it does not hold a charge,
d isassem ble the booster and replace the
accumulator valves.
pedal several 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.
as a fluid leak from the mounting bracket vent
hole. The booster must be removed from the
vehicle and disassembled. The input rod bore
should be checked for any scratches that may
cause the leak. If scratches are present, the
BRAKES 5-3