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BRAKE JOB: GM Acadia / Buick /
Outlook / Enclave
The Lambda Platform is shared with the Chevrolet
Traverse, Saturn Outlook, GMC Acadia and Buick
Enclave. It is largely derived from the GM Epsilon
platform, the same platform that makes the Chevrolet
Malibu and Pontiac G6. These vehicles can be front- or
all-wheel drive. All models have the same rear disc
brake setup with the parking brake in the hat of the
rotor. All Lambda platform vehicles incorporate Tire
Pressure Monitoring (TPMS) ABS and Stabilitrak
electronic stability control.
Gene Markel
10/14/2009
Front Pad Removal
Before replacing the pads, inspect the
master cylinder to ensure that it has not
been topped off before retracting the
pistons into the caliper bores. The front
brakes are a floating dual-piston caliper
type, the pistons are phenolic. The
caliper bridge bolts have a guide pin and
bolt that attach the caliper to the
bracket. Removing the bottom bolt
allows the caliper to be pivoted out of
the bracket. Using a special piston
retractor designed to push evenly on the
dual pistons is highly recommended.
The pads are retained in the bracket
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with anti-rattle clips. To release the pad from the clip, there are tabs at the ends of pad
that are depressed to release the pad. The pads have noise dampening material attached
to the back of the pads.
Front Pad Install
Inspect the dust boots for damage and replace if necessary. Inspect the guide pins and
replace and lubricate if necessary. The boot is
to be seated in the grooves of the caliper
bracket and guide pin.
Install new anti-rattle clips and pads, rotate
the caliper and align the flats on the guide pin
to the mounting ear of the caliper. Torque the
guide pin bolts to 64 Nm (30 ft/lbs).
The caliper bracket bolts on this vehicle use
high strength thread locker to hold it in place
(it is the “red stuff”). Make sure to clean the
old thread locker material off the threads with
denatured alcohol before putting new thread
locker on. The bolts should be tightened to a
whopping 129 ft/lbs!
Rear Pads
Inspect the dust boots for damage and replace
the caliper if necessary. Inspect the guide
pins and replace and lubricate if necessary.
The boot is to be seated in the grooves of the caliper bracket and guide pin. Install new
anti-rattle clips and pads rotate
the caliper and align the flats on
the guide pin to the mounting ear
of the caliper. Torque the guide
pin bolts to 64 Nm (30 ft/lbs).
Like in the front, the rear caliper
brackets use thread locker. Make
sure to clean threads. Then torque
the bolts to 148 ft/lbs.
Rotor and Hub Inspection
Specifications:
Front Brakes
•
New
thickness:
29.0
mm
(1.14”)
•
Min
thickness:
27.5
mm
(1.08”)
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• Max allowable assembled lateral runout: 0.06 mm (0.002”)
• Max allowable scoring: 1.50 mm (0.059”)
• Max allowable thickness variation 0.025 mm (0.001”)
Rear Brakes
• Min thickness: 18.4 mm (0.72”)
• New thickness: 20 mm (0.79”)
• Max allowable assembled lateral runout: 0.06 mm (0.002”)
• Maximum allowable scoring: 1.50 mm (0.059”)
• Max allowable thickness variation: 0.025 mm (0.001”)
Rotor Lateral Runout
Inspection Procedure
The hub and rotor are matched
with the rotor indexed to the hub
and secured with a Torx setscrew.
Three lugs should be used to
ensure the rotor is secured to the
hub. Attach the dial indicator to
the steering knuckle and position
the indicator at 90º to the rotor
surface approximately 12.7 mm
(0.50”) from the rotor. Replace
any rotor that is worn or
machined below this
specification.
If the rotor is within runout specification, new pads and anti-rattle clips can be installed.
If the rotor is out of specification for lateral runout, a shim between the hub and rotor
can correct the runout.
Shim Installation Procedure
GM has approved the shims from Brake Align for
the correction of the runout for rotors machined on
both on- and off-vehicle lathes. Mark the high
spot on the rotor and the stud closest to the high
spot. To check the bearing hub, remove the
caliper bracket and rotor.
Remove the caliper bracket. It is secured to the
knuckle with 19 mm bolts with thread lock
adhesive. When replacing the bracket, clean the
bolt and apply thread lock adhesive to the center
section of the threads. Torque the front caliper
bracket mounting bolts to 175 Nm (129 ft/lbs).
The torque the rear to caliper bracket mounting
bolts to 200 Nm (148 ft/lbs). Remove the Torx
retaining screw and rotor. The hub is checked at
the outer machined surface with the indicator at
90º to the rotor’s surface.
Mark the hub for run out and the stud closest to the high spot. The machined surfaces of
the hub and rotor should be cleaned before the shim is installed with the V-notch aligned
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with “high spot” on the vehicle hub. Reinstall the rotor and torque the retaining screw to
12 Nm (106 in/lbs).
Parking Brake
The parking brake is located in the hat section of the rear rotor. It is applied
mechanically by a cable actuated cam and lever located in the bottom of the backing
plate. The shoes are attached to the backing plate with a pin and leaf spring. The shoes
are held against the cam and lever with a spring.
A spring is also used to hold the shoes against the adjusting screw. The shoes are
adjusted by rotating the star wheel on an adjusting screw located at the top of the
backing plate. There is an
adjusting slot located in the hat
section of the rotor. It will
require an old fashioned adjusting
spoon to reach the star wheel.
The method of adjustment is to
turn the rotor and adjust the star
wheel until the shoes drag on the
drum. Then back off the adjusting
star until the rotor turns free. The
rotor should be secured with the
retaining screw and three lug nuts
when the parking brake shoes are
adjusted.
Bleeding
Like most modern brake systems
with ABS, the system has an
automated bleed procedure that
requires a scan tool. An automated bleed is required if a hydraulic component like the
modulator unit is replaced. Even if you are performing a gravity, pressure or manual
bleed, it is a good idea to run an automated bleed procedure as a way to ensure the there
is not any air trapped in the brake modulator or proportioning valve assembly.
The bleeding sequence is left front, left rear, right front and right rear. If pressure
bleeding, GM recommends between 25-30 psi.
Service Hints
What if the booster does not feel right?
If the brake booster activates excessively or if excessive effort of the brake pedal is
consistently required, Hydraulic Brake Booster “HBB” calibration may be needed. To
do this, it will require a scan tool with the right software. The procedure is simple and
requires pressing the brake and gas in the right sequence.
What if the brake pedal squeaks on application?
TSB 08-05-22-002B is one of the most curious on record for a manufacturer. The
bulletin covers all of the the Acadia and a lot of GM vehicles from 2004-2008.
The bulletin states: Some customers may comment on a squeak noise when the brake
pedal is applied or when released. This noise is normally heard when the brake pedal is
slowly applied with the engine on or off, but can occur when the brake pedal is released.
The noise may be isolated to the master cylinder area.
To correct the problem, GM advises removing as much of the old brake fluid from the
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master cylinder as possible and refill with new DOT 3 brake fluid. Start the vehicle and
fully cycle the brake pedal until the noise diminishes to allow the new fluid to enter the
system. Was it a bad batch of brake fluid? GM has been silent on the cause.
What if the customer complains of ABS noise during first driving? (Enclave,
Acadia and Outlook 2007 & 2008 Model Years)
Some customers may comment on excessive ABS initialization noise, which may be
mistaken as front suspension noise. In addition, customers of 2008 model year vehicles
may comment on traction control sensitivity. The ABS unit runs diagnostic routines as
soon as the vehicle reaches 15 km/h (9 mph). Some customers may find the valve noise
objectionable.
The cure is to re-flash the module so the self-test is less noticeable. Prior to
programming, you will need to know the tire size. Calibrations for 2008 model year
vehicles contain additional software to reduce the traction control sensitivity.
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