7-4 Brake System
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Brake Noise
Squeak/Squeal
The factory installed brakelining in Hummer vehicles is
made from asbestos free materials. These materials have
different operating characteristics than previous lining ma-
terials. Under certain conditions, asbestos free lining may
generate some squeak, groan or chirp noise. This noise is
considered normal and does not indicate a problem. The
only time inspection is necessary, is when noise becomes
constant or when grinding, scraping noises occur.
Constant brake squeak or squeal may be due to linings that are
wet or contaminated with brake fluid, grease, or oil. Glazed
linings and rotors with hard spots can also contribute to
squeak. Dirt and foreign material embedded in the brake lining
can also cause squeak/squeal.
Loud brake squeak, squeal, scraping, or grinding sounds are a
sign of severely worn brake lining. If the lining has worn com-
pletely through in spots, metal-to-metal contact occurs. If the
condition is allowed to continue, rotors can become so scored
that replacement is necessary.
Thump/Clunk
Thumping or clunk noises during braking are frequently
not
caused by brake components. In many cases, such noises are
caused by loose or damaged steering, suspension, drive line, or
engine components. However, calipers that bind on the slide
surfaces can generate a thump or clunk noise. Loose adapter
bolts or halfshaft-to-rotor bolts will cause noise.
Chatter/Shudder
Brake chatter is usually caused by loose or worn components,
or glazed/burnt lining. Rotors with hard spots can also contrib-
ute to chatter. Additional causes of chatter are out-of-tolerance
rotors, brake lining not securely attached to the shoes, loose
wheel bearings and contaminated brake lining.
Brake Lining Contamination
Brake lining contamination is a product of leaking calipers,
driving through deep water puddles, or lining that has become
covered with grease or oil due to leaking axle seals.
Wheel and Tire Problems
Some conditions attributed to brake components may actually
be caused by a wheel or tire problem.
A damaged wheel can cause shudder, vibration and pull. A
worn or damaged tire can also cause pull.
Severely worn tires with little or no tread left can produce a
grab-like condition as the tire loses and recovers traction.
Flat-spotted tires can cause vibration and wheel tramp and gen-
erate shudder during brake operation.
A tire with internal damage such as a severe bruise or ply sepa-
ration can cause pull and vibration.
Diagnosing Parking Brake Problems
Parking Brake Problem Causes
In most cases, the actual cause of an improperly functioning
parking brake (too loose/too tight/won’t hold), can be traced to
a rear brake component.
The leading cause of improper parking brake operation, is
excessive clearance between the brake pads and the rotor
surface. Excessive clearance is a result of lining and/or ro-
tor wear or inoperative adjuster components.
Inspect and adjust parking brake lever or linkage as necessary.
BRAKE SYSTEM TROUBLESHOOTING
Parking Brake Does Not Hold Vehicle
1. Check parking brake adjustment and ensure linkage and
cables operate freely. Adjust parking brake lever and/or
cables or replace damaged and worn parts.
2. Inspect rear brake caliper brake pads for serviceability.
Minimum brake lining thickness is 1/8 in. (3.2 mm).
Replace all rear brake pads if any pad does not meet
thickness specifications.
3. Check caliper for binding or dragging. Check for binding
caliper guide pins.
Low or Spongy Brake Pedal on First Application
or Pedal Goes to Floor
CAUTION:
The HUMMER is equipped with DOT 3 brake
fluid.
Do not mix with other brake fluids
. Failure to use the
proper brake fluid will damage the brake system.
WARNING: Always wear eye protection when bleeding
brakes. Failure to do this may cause personal injury if
brake fluid comes in contact with eyes.
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