How do you test for runout?

Author

Emily Carr

Published Feb 25, 2026

How do you test for runout?

Runout is measured using a simple height gauge on the reference surface. The datum axis is controlled by fixing all datum points and rotating the central datum axis. The part is usually constrained with V-blocks, or a spindle, on each datum that is required to be controlled.

Thereof, what is acceptable rotor runout?

The maximum allowable runout at the rotor friction surface is 0.002 inch (0.050 mm) as stated by most manufacturers.

Likewise, what is lateral runout on brake rotors? Lateral runout is the amount of side to side movement of the rotor as it rotates. Today's vehicles have extremely tight lateral runout specifications. Most vehicles have a specification of two-thousandths of an inch or less.

Also to know is, how do you fix a rotor runout?

Shimming the Rotor

Flange runout can be corrected with tapered shims that are available to correct a runout of 0.003inch (0.075 mm) to 0.009 inch (0.230 mm) A runout of more than 0.005 inch (0.125 mm) at the bearing flange cannot be corrected by the use of a shim.

How do I find lateral runout?

Measure lateral runout with a dial indicator. If it is excessive, use an outside micrometer to measure the thickness of the rotor and compare it to the minimum thickness stamped on the rotor. This process is checking the rotor for parallelism.

What is bearing runout?

Run-out or runout is an inaccuracy of rotating mechanical systems, specifically that the tool or shaft does not rotate exactly in line with the main axis. In the case of bearings, run-out will cause vibration of the machine and increased loads on the bearings.

What causes rotor runout?

When a brake rotor deviates from its axial plane viewed from the front edge of the rotor, this refers to a "wobble" of the rotor as it rotates. A large burr or contamination (caused by rust or grit buildup) may create an uneven mounting surface that will cause the rotor to rotate off its intended axis.

What is flange runout?

The Hydratight Runout Tool is a hand actuated assembly that measures flatness and circular out-of-roundness of flanges.

How do you measure radial runout?

Radial Run-Out is measured by placing a run-out gauge against a smooth section of the tread near the center of the tire and then rotating the wheel and tire by hand through one complete revolution.

How do you check brake drum runout?

The most accurate way to measure run-out is using a brake lathe in good condition and a dial test indicator rigidly mounted so that it will reach into the drum approximately 3/4 of an inch. (Granger 1ZRT2 dial indicator example).

What is excessive runout?

Lateral wheel runout refers to how much a wheel or tire “wobbles” as it rotates. This unbalanced distribution of weight can cause vibrations or premature wear on your tires. Several different factors can cause excessive wheel runout, including rim, wheel and tire mounting.

How do you know if your rotor is warped?

If you notice your steering wheel or brake pedal wobble when you apply the brakes to slow down or stop, chances are your rotors are warped. If the warp isn't too bad, you might not really notice the shaking. If the warp is serious, you'll definitely feel the vibration.

How do you check brake rotor thickness?

This level can be found engraved on the sides of the rotor, within the veins of the rotor, or on the hat of the rotor. Use a micrometer at the thinnest point on the surface of the rotor where it meets the pads to measure the minimum operational thickness.

What is disc run out?

The term "runout" is used to describe the amount of wobble occurring when an element rotates. In a disc braking system, the brake rotor runout must be minimized so that the brakes do not shake and vibrate when engaged.

How is rotor life measured?

Measuring Rotor Thickness. It's impossible to tell how much life is left on the brake rotors by simply looking at it.
Visible Cracks. One of the most obvious ways to check when your rotors need to be replaced is through visible cracks.
Grooves.
Rotor Edge Lip.
Heat Spots.
Rust.
Warped Rotors.

What is radial runout?

Radial runout involves distance discrepancies from one point to another. The greater this discrepancy, the more it will cause the wheel to bounce up and down as it rotates. This bouncing causes the vibrations that often travel up through the steering column, becoming noticeable inside of the car.

What is a rotor shim?

Brake shims are thin layers of rubber or metal that fit between the brake pads and the rotors to correct small imperfections that cause brake noise. They keep the pads and rotors from banging against each other or squealing.

What tool measures rotor thickness?

micrometer

How do I know when my rotors need to be replaced?

It could represent four signs that it's time to replace your brake rotors.

Vibrating Steering Wheel. If you feel pulsing in the brake pedal and vibration in the steering wheel when you slow down, your rotors could be signaling trouble.
Intermittent Screeching.
Blue Coloration.
Excessive Wear Over Time.

What can happen if a brake disc is too thin?

When a rotor is too thin, it overheats and warps, leading to an annoying vibration or pedal pulsation. When rotors were thicker, they could take the wear from the brake pads, be machined and still have enough metal left to dissipate the heat.

How is thickness variation measured?

Run out needs to be measured with a dial indicator with the rotor mounted on the vehicle however, DTV can be measured using a precision micrometer off the vehicle. This is done by measuring the thickness of the rotor 25mm in front of the outer edge.

How long do front brake discs last?

In average use on an average car with an average driver , front discs should give 20 K miles , possibly more. However , if the car is used very intermittently and not very hard they could die due to corrosion in way less than that.

How is parallelism measured in rotor?

Inspect the rotor for parallelism. Using a brake rotor micrometer, measure rotor thickness, one inch from the outer edge, at six to eight clock position points. Compare your findings to the specification. Generally speaking, maximum allowable parallelism should be about 0.0005 inch.

What is an edge code?

Edge Code is a lightweight text editor for web developers and designers who work with HTML, CSS and JavaScript. Built on the foundation of the open source Brackets project and designed to work in the browser, it speeds up development time by displaying code changes directly on the screen.

What is the minimum thickness of brake discs?

37 mm

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How do you test for runout?