How To Repair Lateral Runout Disc Thickness Variation

Disc Thickness Variation (DTV) is where the rotor or disc varies in thickness as indicated in the diagram.

DTV causes torque variation with symptoms such as (i) Pedal pulsation equally the rotor passes through the caliper/pads with lower pedal efforts very noticeable and higher pedal efforts less noticeable. This problem is magnified as the rotor gets hotter i.east. subsequently travelling down an incline with the brakes on. (ii) Steering wheel oscillation, left to right which is not noticeable if the rotors are in stage. (iii) Vibration through the floor of the vehicle.

DTV is the uneven wear of the rotor during service. Often this does not become apparent until 10,000 to 15,000 kms afterwards disc machining or replacement. Poorly serviced calipers can accelerate the occurrence of DTV as tin high levels of rotor run-out at fitment (greater than 0.10mm). This is non generally visible to the human center and must be measured with a micrometer. It is often caused past off-brake wear resulting in apartment spots or thin sections of the disc.

In that location can exist thick or thin parts of the rotor which tin cause the feeling of a variation in the clamping pressure level betwixt the brake pads and the rotor

Run out needs to be measured with a dial indicator with the rotor mounted on the vehicle however, DTV tin exist measured using a precision micrometer off the vehicle. This is done by measuring the thickness of the rotor 25mm in front of the outer border. Measurements should be taken at a minimum of 10 points around the circumference and there should be no greater variance than 0.03mm between any of these measurements.

To right the problem the rotor should be replaced or machined with a light skim to clean up any DTV flat spots. If the vehicle is using ceramic pads, the rotor must be machined as part of every brake job. Calipers should be overhauled, side pins must move freely and the piston seals must be checked for practiced condition or replaced. On-vehicle machining eliminates variation in axles, bearings etc.

To minimise the touch on of Disc Thickness Variation rotors should be machined to clean upward whatever flat spots. Where ceramic pads are used the rotor must be machined with every restriction job. DTV volition not occur if in that location is zero rotor run-out. On-vehicle machining eliminates variation in axles, bearings etc. Vehicle design, tolerance variations and full general wear and tear may withal mean that in some instances goose egg run-out tolerance cannot be achieved. Rotor run-out should be measured with an authentic punch gauge as less run-out leads to slower DTV generation. A quality torque wrench should exist used to fasten "hat"-blazon rotors to the hub with wheel nuts and index rotors on the hub to minimise run-out. Installed run-out should exist less that 100μm (0.1mm) however when this cannot be achieved checks should exist made to the bearings, flange, stub axle and rotor lid. When tightening cycle nuts an air powered "rattle" gun should not exist used merely instead it is recommended that hand tools be used finishing with a quality torque wrench to avoid baloney.

Source: https://www.bendix.com.au/bendix-news/disc-thickness-variation-dtv-issue-14

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