Hummer H1 (2002+). Manual - part 112
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Brake System 7-7
®
05745159
HYDRO-BOOST SYSTEM DIAGNOSIS
Noise Diagnosis
The following noises are associated with the hydro-boost and
may or may not be cause for concern. 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 moan or low frequency hum usually 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 steer-
ing 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 sys-
tem. Check the fluid level and fill if needed. The system
must then sit for one hour to remove the air.
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. If this sound
continues however, 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
Accumulator Leakdown Test
in this section.
PROBLEM
POSSIBLE CAUSE
CORRECTION
Slow Brake Pedal
Return
or
Brakes Apply When
Turning Steering
Wheel
1.
Damaged/broken return spring.
2.
Excessive seal friction in booster.
3.
Faulty spool action.
4.
Restriction in return line from booster to
pump reservoir.
5.
Damaged input rod end.
1.
Replace spring.
2.
Replace the hydro-boost.
3.
Flush the steering system while pumping the
brake pedal.
4.
Replace the line.
5.
Replace the hydro-booster.
Grabs Suddenly
or
Booster Chatters -
Pedal Vibrates
1.
Faulty spool action caused by contami-
nation.
2.
Power steering pump belt slips.
3.
Low fluid level in power steering pump.
1.
Flush steering system while pumping brake pedal.
2.
Replace tensioner and/or belt.
3.
Fill reservoir and check for external leaks.
Accumulator
Leak-Down
Reserve System
Does Not Hold
Charge
1.
Contamination in steering hydro-boost
system.
2.
Internal leakage in accumulator system
1.
Flush steering system while pumping brake pedal.
2.
Replace hydro-boost.
Excessive Brake
Pedal Efforts
1.
Loose, glazed, or broken pump belt.
2.
No fluid in pump reservoir.
3.
Leaks in system hoses.
4.
Leaks at tube fittings and connections.
5.
Leakage at pneumatic accumulator seal.
6.
Leakage at piston seal.
7.
Leakage at input seal.
8.
Leakage at cover-to-housing seal.
9.
Leakage at spool plug seal.
10. Leakage at ball plug
1.
Replace tensioner and/or replace belt.
2.
Fill reservoir and check for external leaks.
3.
Replace faulty parts.
4.
Tighten fittings or replace tube seats or O-rings.
5.
Replace O-ring.
6.
Overhaul with new seal kit.
7.
Overhaul with new seal kit.
8.
Overhaul with new seal kit.
9.
Overhaul with spool plug seal kit.
10. Replace hydro-boost.
NOTE:
The power steering fluid and brake fluid cannot be mixed. If the brake seals contact steering fluid or the steering seals
contact brake fluid, seal damage will result.