The key steps during disc
brake service include determining rotor refinishing or replacement, properly
cleaning all brake components (including items such as hub, rotor, and wheel
mating surfaces), properly refinishing the rotor (if applicable), and properly
reassembling the brake assembly using the proper tools and torque
specification.
Here are some tips to ensure
a successful brake service and prevent vibration and brake noise. Always refer
to the appropriate Service Information or latest bulletins for specific
procedures. GM bulletin #00-05-22-022L is a good resource that updates and
centralizes all of GM's standard brake service procedures.
Rotor
Refinishing
When it's determined that a
rotor must be refinished, use a brake micrometer to measure the rotor. Multiple
measure points should be taken and the lowest measurement recorded. Reference
the Minimum Thickness specification stamped on the backside of the rotor and
the Discard specification in the Service Information before refinishing the
rotor. (Fig. 2) Do not refinish new rotors or
remove any special coating that may be applied on some ACDelco replacement brake
rotors.

Clean all of the mating
surfaces between the hub, rotor and wheel. Cleaning all mating surfaces and
making them free of corrosion, burrs and other debris is critical and must be
performed whether using an on-car or bench lathe refinishing procedure. Prior
to making the cut when refinishing, install the recommended clip-on style disc
silencer supplied with the lathe. Using the silencer will help prevent chatter
from occurring during the cut.
After completing the
refinish, sand both sides of the rotor for approximately one minute per side
using 130-150 grit sandpaper to obtain a non-directional finish. Wash the rotor
with mild soap and water or wipe it clean with ACDelco brake parts cleaner,
part number 10-6012. Thoroughly cleaning the rotor will prevent the possible
transfer of finite metal dust left as a by-product of machining to the pad
material, reducing the chance for squeaks or other noises to occur.
Do
not clean the rotor with a brake cleaner solvent-based product.
Preventing
Pulsation
Any time a brake rotor is
refinished, measuring lateral runout (LRO) will help to prevent pulsation and
customer come-backs. Pulsation is caused by brake rotor thickness variation,
which is usually the result of excessive LRO or brake rotor corrosion.
Lateral runout is a
measurement of the waviness of the rotor face. The GM specification for
excessive LRO is more than 0.050 mm (0.002 in.). Excessive LRO occurs to a
rotor when the brakes are not applied. When the vehicle is being driven, any
high spot on the rotor rubs the brake pad once per revolution. Eventually, the
high spot is worn down, resulting in a thin spot on the rotor (rotor thickness
variation) and pulsation that is transferred through the brake pedal when the
brakes are applied.
Rotor corrosion is another
form of thickness variation. In cases where rotor corrosion is cosmetic,
refinishing the rotor is unnecessary. More extensive corrosion may be the
result of a build up, mostly on the rotor material surface, caused by a
combination of corrosion, pad material and heat. In some instances, cleaning up
this type of corrosion may require more rotor material to be removed than
typical refinishing.
When measuring LRO, rotate
and locate the point on the rotor where the lowest dial indicator reading is indicated.
Set the dial indicator to zero. Rotate the rotor from the low point and locate
the point with the highest dial indicator reading (the high spot). (Fig. 3)

In addition, index-mark the
rotor and a wheel stud so that it is in the same position as it was prior to
service.
If LRO is excessive, use
Brake Align® correction plates or refer to the appropriate Service
Information to correct the lateral runout.
Installation
Tips
Reinstall the rotors on both
sides of the vehicle following these steps:
•
Reinstall the calipers
and pads. Use a thin film of ACDelco high temperature silicone grease, part
number 10-4019, on caliper sides, rubber components and disc pad shims, which
will allow the shims to withstand normal brake pad movement without damage and help
dampen vibration.
•
Pump the brakes to
pressurize the calipers
•
Remove the lug
nuts/conical washers (if installed for refinishing the rotors on the vehicle).
•
Install and properly
torque the wheels
It is critical to use the
proper tools (torque stick or torque wrench) to torque the wheels to
specification as referenced in the Service Information. (Fig. 4)
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