Hummer H1 Service Manual page 445

7-6 Brake System
Brake Chatter
On some new vehicles, roughness or a chatter sound from the
brakes may be noticed during low speed brake application. The
noise is a result of the lining edges of an unburnished brake pad
rubbing against the rotor. Burnishing is a part of the vehicle
break-in process which fully seats and conditions new brake
pads. Although annoying, the brake noise is not detrimental to
vehicle safety or performance, and will eventually be elimi-
nated through normal brake use.
If chatter or roughness persists on a new vehicle, then chamfer-
ing of the brake pad lining edges can be performed. Chamfer-
ing of the brake pad is done by slightly grinding or filing the
edge of the pad lining on a grinding wheel.
To complete the chamfering procedure:
1. Remove the eight service brake pads from the vehicle.
Mark each pad for vehicle and caliper location.
2. Chamfer (grind or file) the brake pad lining edges. Ensure both
brake pad lining edges are chamfered on each of the eight
brake pads (Figure 7-2). Make sure pads are flat and even.
3. Install eight service brake pads at the original vehicle and
caliper location.
4. Operate vehicle and check brakes for proper operation.
VIEW DEPICTS BRAKE PAD
AFTER BEING CHAMFERED
1/4"
18°
SIDE VIEW OF BRAKE
PAD LINING EDGE
Figure 7-2: Chamfering Brake Pad
Booster or Pedal Pulsation
1. Check hydro-boost. Depress brake pedal several times,
with engine off, to exhaust accumulator pressure. Depress
brake pedal and start engine.
a. Brake pedal should fall, then push back against opera-
tor's foot.
b. Perform pressure test (Section 8).
c. Replace hydro-boost if not operating properly.
2. Check halfshaft and rotor mounting for missing or loose capscrews.
Replace inclined-cam washers, apply a thread locking compound and
torque capscrews to 57 lb-ft (77 N•m).
3. Check brake rotor lateral run-out. Refinish any rotor not
meeting specifications. Refer to Checking Lateral Runout
in this section for more information.
4-1-00
______________________________________________________________
BRAKE PAD
LINING EDGE
BRAKE PAD LINING EDGE
AREA TO BE REMOVED BY
CHAMFERING (GRINDING)
S07-043
Erratic Braking Action
1. Check for correct tire pressure.
2. Check brake pads for binding as a result of corrosion or dirt.
Check brake pads for excessive wear. Minimum brake lining
thickness is 1/8 in. (3.2 mm). Replace brake pads as sets
(front or rear) if any pad does not meet specifications.
3. Check brake calipers for binding as a result of corrosion or
dirt. Check for seized or binding brake caliper pistons.
Repair any binding or seized caliper pistons. Check brake
rotors for free movement. If rotors do not move freely,
remove calipers and clean caliper guide pins (Figure 7-3).
NOTE: Calipers pins must be replaced in pairs. Caliper pins
and bushing should be lubricated with an approved brake com-
ponent lubricant.
4. Check for leaking caliper piston seals. Replace or rebuild
any calipers with leaking seals.
5. Check rotor for glazing or scoring. Turn the rotor if glazed
or scored. Do not exceed the minimum thickness shown on
the inside of the rotor hat section. It is not recommended
that rotors be turned when spotted or heat checked.
6. Check for damaged brake lines. Replace any damaged
brake lines.
7. Check ABS operation. Check ABS warning lamp.
Perform a 20 mph hard deceleration on a slippery surface
(sand, gravel, snow, etc). If one or more wheels lock repair
the ABS. Refer to ABS diagnostics in this secion.
8. Check toe adjustment. Adjust toe, if necessary. Refer to
Section 5.
ROTOR
BRAKE PAD
BRAKE
LINE/HOSE
COUPLING
AND COPPER
WASHER
BUSHING
AND
SLEEVE
CALIPER
Figure 7-3: Brake Caliper and Brake Pads
®
ADAPTER
BRAKE
PAD
COOLING
FINS
CALIPER
GUIDE PINS