Posted by PeteL on February 10, 03 at 18:28:59:
In Reply to: Brake wear / Praise Brakes / Poor brakes on Subs - Lets get a new thread going. posted by PeteL on February 10, 03 at 17:55:39:
Warranty Admin. - Brake Rotor Warranty Service
Procedure #00-05-22-002
Brake Rotor Warranty Service Procedure
1995-2000 Passenger Cars and Light Duty Trucks
This bulletin outlines GM's standard procedures and guidelines for brake rotor service and brake wear.
Important
Certain conditions may apply to individual vehicles regarding specific repairs which differ from those outlined in this bulletin.
Refer to those specific repairs in applicable bulletins.
Original equipment rotor surfaces are ground to ensure smooth finish and parallelism between mounting and friction surfaces.
New rotors SHOULD NOT be resurfaced before installation. When rotor turning is necessary, it is essential that you use a high
quality brake lathe. Rotors, when remounted on the hub, should have less than .080 mm (.003 in) lateral runout. Brake rotors
should only be turned when one of the following rotor surface conditions exist:
1.Severe scoring -- depth in excess of 1.5 mm (0.060 in).
2.Pulsation concerns from:
Lateral runout in excess of .080 mm (.003 in).
Thickness variation in excess of 0.025 mm (0.001 in).
Excessive corrosion on rotor braking surfaces.
Rotors are not to be resurfaced in an attempt to correct the following conditions:
Noise/squeal
Cosmetic corrosion
Routine pad replacement
Discoloration/hard spots
Explanation of Brake Rotor Warranty Service Procedure
Rotor refacing during normal pad replacement is not necessary.
Rotor refacing for cosmetic corrosion is unnecessary. Clean up of braking surfaces can be accomplished by 10-15
moderate stops from 62-75 km/h (35-40 mph) with cooling time between stops.
Rotor service is ineffective in correcting brake squeal and/or premature lining wear out and should not be used to
address these conditions unless specifically directed by a service bulletin.
When installing new rotors, DO NOT reface them. If a new rotor has more than .080 mm (.003 in) lateral runout when
properly mounted on the hub, it may be machined using an approved on-car lathe.
Ensure bearing flanges and rotor mounting surfaces are free of corrosion when installing rotors to prevent inducing lateral
runout. Use Kent Moore tool J-42450A to clean the corrosion around the wheel studs.
Always mark the position of the rotor on the hub before removal and reinstall the rotor in the same position. Rotors with
perceived hard spots or discoloration should not be serviced. These conditions are normal. Installation of new rotors
does not require pad replacement. Do not replace pads unless their condition requires it. It is not necessary to replace
rotors in pairs. Rotors may be replaced individually. However, caution should be exercised, as a variance in surface
finish may cause a brake pull condition.
A torque limiting socket or torque wrench must be used to insure that the wheel nuts are tightened to specification. This
should be done in 3 steps using the star pattern:
1.Hand tighten all 5 lug nuts using the star pattern.
2.Tighten all 5 nuts to approximately ½ spec. using the star pattern.
3.Tighten all 5 nuts to full spec. using the star pattern.
Never use lubricants or penetrating fluids on wheel studs, nuts or mounting surfaces. Wheel nuts, studs and mounting
surfaces must be clean and dry.
Brake Service Techniques
1.Clean and lubricate all metal-to-metal contact points (i.e. caliper to knuckle, pad to knuckle, etc).
2.Clean and lubricate slide pins, if applicable.
3.Set correct clearances (i.e. caliper to knuckle, etc), if applicable.
4.Clean rotor and hub mounting surfaces. Use Kent Moore tool J-42450 to clean around the wheel studs.
5.Verify lateral runout of the rotor with a dial indicator (rotor held on hub with 3 or more wheel nuts and washers).
Important
Refer to the appropriate Service Manual for more specific procedures.
Pulsation
Important
Brake pulsation is often caused by factors outside customer control. In these instances, the repair is covered under the GM
New Vehicle Warranty.
Brake pulsation concerns may result from two basic conditions:
Pulsation is caused by brake rotor thickness variation. Thickness variation causes the piston in the brake caliper to
"pump" in and out of the caliper housing. This "pumping" effect is transmitted hydraulically to the brake pedal.
Thickness variation on a new rotor will be virtually undetectable. But if the rotor (as installed on the vehicle) has lateral
runout, it is likely that thickness variation will develop. Pulsation caused by thickness variation will develop on new
vehicles when the tolerances of the hub and rotor stack up with lateral runout in excess of .08 mm (.003 in). Pulsation
that is the result of excessive lateral runout usually develops in 4800-11300 kilometers (3000-7000 miles). Thickness
variation can be induced when uneven torque is applied to wheel nuts (lug nuts). Improper wheel tightening after tire
rotation, spare tire usage, brake inspection, etc. can be the cause of pulsation. Again, it usually takes 4800-11300
kilometers (3000-7000 miles) after this event for the condition to surface. The owner or driver does not usually make the
connection between the service event and the awareness of the pulsation. The proper usage of torque wrenches and/or
torque sticks (torque limiting sockets) will greatly reduce or eliminate the pulsation conditions after wheel service events.
The improper use of impact wrenches on wheel nuts greatly increases the likelihood of pulsation after wheel service.
GM highly recommends the use of on-car brake rotor turning as a method of eliminating the stack up of lateral runout which is a
potential source of brake pulsation. GM has identified superior equipment through testing and evaluation. The
*Pro-Cut PFM900 will consistently deliver machined rotors that meet GM specifications (lateral runout less than .080 mm
(.003 in) and is the only on-car brake lathe that is currently recommended by GM. The use of this on-car rotor turning
technology has proven to significantly reduce the repeat occurrences of brake pulsation.
*We believe this source and their equipment to be reliable. There may be additional manufacturers of such equipment. General
Motors does not endorse, indicate any preference for or assume any responsibility for the equipment from this firm or for any
such items which may be available from other sources.
The following are examples of pulsation conditions and reimbursement recommendations:
1.If a customer noticed the condition after 4800-11300 kilometers (3000-7000 miles) and it gradually got worse, normally
the repair would be covered. The customer may tolerate the condition until it becomes very apparent.
2.If a customer indicated they had wheel service, ask who performed the service. Then:
If a dealer performed the service, consider paying for the repair and then strongly reinforce the use of torque
sticks at that dealer. Two common size torque sticks cover 90% of all GM products. Each technician needs to
use torque sticks properly every time the wheel nuts are tightened.
If the customer had the wheel service done outside of our dealer network, normally GM would not offer any
assistance.
Customer assistance concerning brake pulsation and brake wear should always take into account the individual circumstances
on a case by case basis. The recommendations mentioned previously should only be used as a general guide. REMEMBER
THAT CUSTOMER SATISFACTION IS CRITICAL TO GM AND THAT OFTEN IT IS IN GM'S BEST INTEREST
TO SATISFY AND EDUCATE THE CUSTOMER CONCERNING FUTURE BRAKE SERVICE.
Rotor Grooving
Excessive grooving can be caused by foreign material in contact with the rotor, but most often rotor grooving is the result of
normal brake wear. Do not resurface rotors for light grooving. Resurface rotors only when grooves of 1.5 mm (0.060 in) or
deeper are present.
A dime may be used to determine disc brake groove depth. Place a dime in the groove, with Roosevelt's head toward the
groove. If the dime goes into the groove beyond the top of his head, the groove exceeds 1.5 mm (0.060 in) and the rotor
should be serviced. In Canada, if any portion of the letters of "Canada" are covered, the rotor should be serviced. If the groove
is too narrow for the dime to be inserted, it is not a cause for concern.
High Pedal Effort
Follow the Service Manual diagnostic procedures for this condition. Service (replace or resurface) rotors if they have been
recently resurfaced. The surface finish may be out-of-specification.
Lightly Rusted Rotors
Light surface rust on rotor braking surfaces is often cosmetic and can be eliminated during a few normal driving stops. Rusting
may occur when a vehicle is not driven for extended periods. Rotors with surface rust on unsold new cars can usually be
burnished clean by performing 15 moderate stops from 62-75 km/h (35-40 mph) with cooling time between stops.
Facts About Brake Noise
Brake noise is normal and differences in loading, type of driving, or driving style can make a difference in brake wear on the
same make and model. Depending on weather conditions, driving patterns and the local environment, brake noise may become
more or less apparent.
Brake noise is caused by a "slip stick" vibration of brake components. While intermittent brake noise may be normal,
performing 3-4 aggressive stops may temporarily reduce or eliminate most brake squeal. If the noise persists, a brake
dampening compound may be applied to the back of each pad. Use Permatex Disc Brake Quiet #126hb, or equivalent. Also,
clean and lubricate all metal-to-metal contact areas between pads, pad guides, caliper and knuckles with a thin layer of high
temperature silicone grease. This allows parts to slide freely and not vibrate when moving relative to each other.
The following noises are characteristic of all braking systems and are unavoidable. They may not indicate improper operation of
the brake system.
Squeak/Squeal Noise
Occurs with front semi-metallic brake pads at medium speeds when light to medium pressure is applied to the brake
pedal.
Occasionally a noise may occur on rear brakes during the first few stops or with cold brakes and/or high humidity.
Grinding Noise
Common to rear brakes and some front disc brakes during initial stops after the vehicle has been parked overnight.
Caused by trace corrosion on the metal surfaces during vehicle non-use. Usually disappears after a few stops.
Groan Noise
A small groan may be heard when stopping quickly or moving forward slowly from a complete stop. This is normal.
Brake Wear
Several factors impact brake lining wear and should be taken into account when reviewing related issues.
The following are conditions that may accelerate brake lining wear:
Heavy loads
High temperatures
Towing
Mountainous terrain
City Driving
Aggressive driving
Driver braking characteristics (left foot)
The following are conditions that may extend brake lining wear:
Light loads
Highway driving
Conservative driving
Level terrain
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