Brake Rotor - Hummer H1 Service Manual

7-32 Brake System

BRAKE ROTOR

Cleaning and Inspection
NOTE: Clean all components, examine for wear or damage,
and replace if necessary (Figure 7-38).
1. Remove brake rotor.
NOTE: Clean rusted or scaled rotor braking surfaces before at-
tempting inspection or measurement.
2. Mount rotor in brake lathe and turn while cleaning
surfaces with abrasive crocus cloth.
3. Inspect rotor for heat checks, nicks, broken cooling fins,
scoring, discoloration, and pitting. It is not recommended
that rotors be turned when spotted or heat checked.
BRAKE ROTOR
Figure 7-38: Brake Rotor and Cooling Fins
NOTE: Clean debris from cooling fins if necessary.
REFINISHING BRAKE ROTORS
Refinish rotors only under the following circumstances:
1. There is a complaint of brake pulsation.
2. There is excessive scoring.
Brake rotors have a minimum thickness dimension cast into
them. This dimension is the minimum wear dimension and not
a refinish dimension. Do not use a brake rotor that will not
meet the dimensions shown in the specifications. Original
equipment rotors are finished to 0.25-1.27 micrometers (10-50
microinches).
Accurate control of rotor tolerances is necessary for the proper
performance of disc brakes. Machining should be done only
with precision equipment. Service the machining equipment on
a regular basis following the manufacturer's recommended
maintenance procedures.
When you refinish rotors, make sure the attaching adapters,
tool holders, vibration dampeners, and tool bits are in good
condition. Always use sharp cutting tools or bits and use only
replacement cutting bits recommended by the equipment man-
ufacturer. Dull or worn tools leave a poor surface finish that
will affect initial brake performance. Vibration dampening at-
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COOLING FINS
tachments should always be used when refinishing braking sur-
faces. These attachments eliminate tool chatter to allow for a
better surface finish. Make sure these adaptors are clean and
free of nicks. The optional swirl pattern finish will provide the
best initial braking effectiveness. For this, use a sanding disc
power tool with 120 grit disc for about 10 seconds per side.
Checking Lateral Runout
1. Mount dial indicator with stylus contacting rotor surface 1
in. (25 mm) in from outer edge (Figure 7-39).
2. Turn rotor 360° and note total indicator reading (TIR).
If lateral runout exceeds 0.004 in. (0.10 mm) TIR, replace or
refinish rotor.
Figure 7-39: Checking Rotor for Lateral Runout
Checking Thickness Variation
1. Measure thickness variation of rotor with micrometer at
four equally-spaced points around rotor. Measure 1 in. (25
mm) in from outer edge (Figure 7-40).
2. If thickness variation exceeds 0.005 in. (0.13 mm), replace
or refinish rotor.
Refinishing
1. Mount rotor on brake lathe and refinish surface.
2. Replace rotor if refinishing causes rotor to fall below
minimum thickness of 0.815 in. (20.7 mm).
3. Install brake rotor.
Figure 7-40: Checking Rotor Thickness
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ROTOR
ROTOR