GM Century/Lumina/Grand Prix/Intrigue 1997-2000

Brake Rotors

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It should not be necessary to refinish the brake rotors when performing routine brake maintenance such as replacing worn disc brake pads. Refinish a rotor only if a pulsation is felt in the brake pedal and/or there is a scoring of the rotor greater than 0.060 inch (1.5 mm).

All brake rotors have a minimum thickness dimension number cast into them. This dimension is the minimum wear dimension and not a refinish dimension. Do not use a brake rotor that, after refinishing, will not meet the specification shown on the rotor. Always replace it with a new rotor.


NOTE
It is extremely important that a brake rotor have very little lateral runout. It must turn true or the rotor will wobble on the wheel hub. This wobble will force the brake caliper piston to rapidly pulse in and out of the caliper. This results in a pulsating feel to the brake pedal when applied. Whenever a rotor has been separated from the wheel bearing flange, clean any rust or contaminants from the wheel flange and brake rotor mating surfaces. Even relatively small particles of dirt, rust or other foreign material between the face of the wheel hub and the back face of the brake rotor is enough to cause problems. Failure to keep the metal contact mating surfaces clean may result in increased lateral runout of the rotor and brake pulsation.

REMOVAL & INSTALLATION





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Fig. The rotor is removed by sliding it straight off the lug studs

  1. Using a suction gun, remove approximately 2 / 3 of the brake fluid from the master cylinder. The reason for this is that the caliper pistons must be pushed back into their bores so the caliper can be removed from the rotor. This could cause the brake fluid to overflow from the reservoir onto painted surfaces or wiring.
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  3. Raise and safely support the vehicle on safety stands.
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  5. Mark the relationship of the wheel to the hub so it can later be installed in the same relationship. This helps retain the balance of the rotating assembly.
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  7. Remove the tire and wheel assembly.
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  9. It is not necessary to remove the brake lines or parking brake cable (as equipped) when removing a caliper to service the brake rotors. It is necessary to use care not to damage the brake hose by letting the caliper hang. The weight of the caliper can damage the brake hose. Remove the caliper using the procedures found in this section and suspend it from the strut with a wire hook or suitable piece of wire. Do NOT disconnect the brake hose or allow the caliper to hang from the brake line.
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  11. Remove the rotor assembly by simply pulling it off the hub.
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To install:

  1. Clean all parts well. Make sure the metal contact surfaces between the brake rotor and the hub bearing flange are clean. Sandpaper and/or wirebrush these areas to make sure they are clean.
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  3. Install the brake rotor over the hub assembly.
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  5. Install the brake caliper as outlined in this section.
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  7. Install the wheel and tire assembly.
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  9. Carefully lower the vehicle, then fill the master cylinder reservoir to the FULL level with the correct type of DOT 3 brake fluid from a clean, unsealed container.
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  11. Firmly depress the brake pedal three times before moving the vehicle. This reseats the brake pads and moves the caliper pistons back to their operating positions. Do not attempt to move the vehicle until a firm brake pedal has been established.
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INSPECTION





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Fig. A rotor with grooved this deep will have to resurfaced or, more likely, replaced

Thickness Variation Check

The thickness variation can be checked by measuring the thickness of the rotor at four or more points. All of the measurements must be made at the same distance from the edge of the rotor. GM recommends using a micrometer that reads in ten-thousandths of an inch. They feel rotor condition is that critical. A rotor the varies by more than 0.005 inch (0.013 mm) can cause a pulsation in the brake pedal. If these measurement are excessive, the rotor should be refinished or replaced.

Lateral Runout Check

GM recommends that the best way to check lateral runout is with the wheels still installed on the vehicle. This gives a much more accurate reading of the Total Indicated Runout (TIR) under real braking conditions. If equipment is not available to perform the check with the wheels installed, the next best reading can be made with the wheels removed but with the caliper still installed.

  1. Raise and safely support the vehicle. Remove the wheel and tire assembly.
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  3. It is important that, since the wheel has been removed, that the brake rotor be properly retained. Install the wheel lug nuts (some technicians install them backwards to present a flat face to the rotor, depending on the design of the lug nut). Torque them just as if the wheel were installed to 100 ft. lbs. (140 Nm).
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  5. Install a dial indicator to the steering knuckle so that the indicator button contacts the rotor about 1 inch (25mm) from the rotor edge.
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  7. Zero the dial indicator.
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  9. Turn the rotor one complete revolution and observe the total indicated runout.
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  11. The Total Indicated Runout (TIR) must not exceed 0.003 inch (0.080mm).
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  13. If the TIR exceeds specifications, have the rotor refinished or replaced.
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Please note that in some cases, excessive lateral runout of the rotor can be improved by indexing the rotor on the hub, one or two bolt positions from the original position. If the lateral runout cannot be corrected by indexing the rotor, remove the rotor and check the wheel hub for excessive lateral runout or looseness (perhaps the wheel bearings are worn). If the hub lateral runout exceeds 0.0015 inch (0.040 mm), then replace the hub. If the lateral runout of the hub is within specifications, then rotor will have to be refinished at an automotive machine shop or replaced with a new part.

 
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