Brake Rotor, Disc

Brake pulsation (brake roughness) that is present during brake application is caused either by foreign material buildup or contamination on the disc brake hub and rotor braking surface, or by uneven rotor thickness.

If there is a foreign material buildup or contamination found on the disc brake hub and rotor or brake shoe and lining surfaces, hand sand linings and rotors.

Uneven disc brake hub and rotor thickness (thickness variation) may be caused by the following:

• disc brake hub and rotor lateral runout in excess of 0.05mm (0.003 inch) for the front disc brake assembly or 0.20mm (0.008 inch) for the rear brake assembly when the rotor is mounted on the hub
• disc brake caliper drag
• abrasive action of brake lining

If brake pulsation or roughness is present, attempt stopping vehicle with transmission in the NEUTRAL position. If the pulsation or roughness is gone, the drivetrain should be inspected. If pulsation or roughness remains, inspect brakes.

Front and rear disc brake rotor specifications are listed in the Specifications chart at the end of this section.

Runout

Front

Front disc brake rotor lateral runout is the side-to-side movement or wobble of the front disc brake rotor (1125) as it rotates. Excessive runout may cause vibration, brake pedal pumping, low brake pedal (2455) or brake chatter. Use the following procedure to check front disc brake rotor runout.

1. Tighten the front axle wheel hub retainer (3B477) (front brakes only) to eliminate all end play from the front wheel bearing. Be sure the front disc brake rotor can be turned.

2. Attach Dial Indicator with Bracketry TOOL-4201-C or equivalent to some part of the vehicle suspension so the stylus of the indicator touches the surface of the front disc brake rotor approximately 25.4mm (1 inch) from outer edge of the front disc brake rotor.

3. Adjust the dial indicator to mid travel. Zero the scale on the dial indicator. Slowly turn the front disc brake rotor one complete turn and note the high and low readings on the dial. The total between the high and low reading must not exceed the specified runout limit.

4.  CAUTION: Be sure to adjust the front axle wheel hub retainer to specifications after the runout check.

   Refinish or replace the front disc brake rotor as required.

Rear

Check the lateral runout of the rotor by mounting Dial Indicator with Magnetic Base D78P-4201B or equivalent to the rear axle housing so that the indicator contact point rides on the rotor braking surface.

Rotate the rotor/rear hub assembly and observe the dial indicator reading. Maximum lateral runout is 0.20mm (0.008 inch).

Parallelism

Parallelism is the variation in the thickness of the disc brake rotor. If the two rubbing surfaces of the disc brake rotor are not parallel, the disc brake rotor may cause excessive brake pedal travel, a pulsating brake pedal, or noise.

Two methods can be used to check if the two faces of a disc brake rotor are parallel. A micrometer can be used to measure the disc brake rotor thickness at 12 points approximately 30 degrees apart and 25.4mm (1 inch) from the outer edge of the disc brake rotor.

The other method is to measure the disc brake rotor on a precision lathe designed for machining disc brake rotors. Attach two dial indicators, one on each side of the disc brake rotor, so that the stylus on each indicator contacts the rubbing surface, directly opposite each other, approximately 25.4mm (1 inch) from the outer edge of the disc brake rotor.

Zero both indicators and rotate the disc brake rotor while watching both dials. If the total readings of both indicators exceed the specified limit for parallelism, the disc brake rotor must be refinished or replaced.

Refinishing

Front

Do not machine, cut or true up new front disc brake hub and rotors (1102) prior to installation on vehicle. Making a light cut on a new front disc brake hub and rotor may cause excessive runout and result in brake shudder several thousand miles later. It is best to clean oil film off new front disc brake hub and rotor with metal brake parts cleaner F2ZZ-19579-AA or equivalent and install it on vehicle.

Never use a brake lathe that cuts only one face of the front disc brake hub and rotor at a time. It must be a simultaneous straddle cut. All front disc brake hub and rotor refinishing must adhere to the rule that equal amounts of front disc brake hub and rotor stock are removed from each braking surface each time a front disc brake hub and rotor is refinished.

On-vehicle brake lathes machine the front disc brake hub and rotor while it is on the hub and is turning on the same axis as the hub. This procedure reduces front disc brake hub and rotor lateral runout to near zero by cutting the front disc brake hub and rotor perpendicular to the axis of the hub, therefore cancelling the effect of stacked tolerance of the hub, front disc brake hub and rotor and front wheel spindle (3105). Follow the on-vehicle brake lathe manufacturer's instructions on machining procedures.

A bench-mounted disc brake lathe machines the front disc brake hub and rotor to the axis of the lathe arbor and will not reduce total lateral runout associated with stacked tolerances of the hub, front disc brake hub and rotor and front wheel spindle. Follow manufacturer's instructions on machining procedures.

With both types of brake lathes, set cutting tool to just contact the high spots on the front disc brake hub and rotor, then adjust cutting tool to the minimum depth required to clean up the front disc brake hub and rotor face. The total material removed (combination of both sides) must not exceed the minimum discard thickness that is marked on the inside of the front disc brake hub and rotor.

To improve initial brake pedal feel and surface finish on a machined front disc brake hub and rotor, lightly sand rotor surface with 120 grit paper prior to road testing.

Rear

1. If there are just surface irregularities, the rear disc brake rotor may be resurfaced by lightly sanding the face with a fine emery cloth using the following steps.

   1. Remove the wheel (1007).
   2. Remove the rear disc brake caliper (2B120). Refer to Section 06-04.
   3. Lightly sand both sides of the rear disc brake rotor. The back side of the rear disc brake rotor can be sanded at the rear wheel disc brake shield (2C028) where the disc brake caliper normally rides. If scratches or scoring exceed .22mm (.009 inch), the rear disc brake rotor must be resurfaced.

2. NOTE: The rear disc brake rotor must be machined while it is bolted to the rear hub (1109). The rear disc brake rotor and rear hub are mounted as an assembly on the rotor lathe, and then the rear disc brake rotor is machined. Machining the rear disc brake rotor separately and then bolting it back onto the rear hub may cause rear disc brake rotor runout.

   If the rear disc brake rotor has deep scratches or grooves, runout (warped rear disc brake rotor) or incorrect parallelism (thickness variation), it must be resurfaced off the vehicle on a rotor lathe as follows.

   1. Remove the wheel.
   2. Remove the disc brake caliper and support it by a piece of wire. Refer to Section 06-04.
   3. Remove the rotor and rear hub assembly from the vehicle. Refer to Section 06-04.
   4. Resurface the rear disc brake rotor on a rotor lathe. Follow the manufacturer's instructions for the rear disc brake rotor refinishing equipment being used. Minimum thickness for the rear disc brake rotor is 36.3mm (1.43 in.).

Service Limits

 WARNING: NEVER INSTALL A FRONT DISC BRAKE ROTOR THAT HAS BEEN TURNED TO MINIMUM WEAR OR DISCARD THICKNESS.

Measure the thickness of the front disc brake rotor to determine if it is within specifications listed at the end of this section. Front disc brake rotor minimum (discard) thickness is stamped on the front disc brake rotor. Front disc brake rotors have a minimum thickness dimension (minimum wear thickness or discard thickness). This is not the refinishing dimension.