AfterMarketNews AfterMarketNews Auto Care Pro AutoCareCareerHub Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service Speedville

Air Filter Show & Tell: Seeing Is Believing

Air filters are normal wear items that ­require regular checks and ­replacement. Their role is to trap dirt particles that can cause damage to engine cylinders, walls, pistons and piston rings. In fuel-injected vehicles, the air filter also plays...

Read more...

Searching for 'Black Holes': Job Totals Reveal Missed Selling Opportunities

The concept for Maintenance Chronicle is simple: We ask one shop to record their maintenance sales for a two-week period, and then we see what we learn from the results. This edition of Maintenance Chronicle also proved to be valuable for the shop we...

Read more...

Selling Batteries With a State of Health Strategy

Batteries can be an easy sell in some ways ­because all customers ­understand the basic importance of the battery. Good battery = car starts; bad battery = car doesn’t start. Unfortunately, many customers aren’t in the market for that new battery...

Read more...

Saab: Fuel Sending Unit Replacement

The 2006 Saab 9-3 Sport sedan came in on the hook and the tow truck driver said, “I think it needs a fuel pump.” The gas gauge was reading less than a quarter of a tank and the low fuel warning light wasn’t on, so a quick fuel pressure check was...

Read more...

KIA: Brake Light On, Tachometer And Speedometer Inoperative

Applicable Models: 2001 Kia Optima LX, 2.4L Complaint The customer states the red brake light is illuminated on the instrument cluster. The ­customer also states the tachometer and speedometer intermittently stop working. Cause Confirmed the customer’s...

Read more...

Mazda: Fuel System Servicing Precaution

Applicable Models: 2004-’07 Mazda3 2005-’07 Mazda6 2006-’07 MX-5 vehicles During service/removal of fuel system parts on the above vehicles, the memory of the malfunctions and the long-term fuel trim need to be cleared by either removing the...

Read more...

Pulling Codes: Multiple Misfire Personalities

A Story of Codes P0302, 04, 06, 08 & 03   This month’s diagnostic journey begins with a 2008 Land Rover Discovery that is taken in to a local testing facility for an emission test and fails due to a series of misfire codes. Misfire...

Read more...

Using Volumetric Efficiency to Determine the Health of an Engine

Measuring voumetric efficiency can diagnose problems like blocked catalytic converters, bad MAF sensors or vacuum leaks. Glen Beanard show you how to do it with a scan tool. For the complete article, click here.  ...

Read more...

Phoenix Systems Sends Facebook Giveaway Winner to Meet Larry McReynolds for All-Star Race

Phoenix Systems, maker BrakeShot, BrakeStrip and Reverse Brake & Clutch Bleeders, announced the winner of its 2015 Win Race Tickets Facebook Giveaway. Suzanne Cleary Drews from Edgewater, FL, is this year's grand-prize winner. Phoenix Systems will...

Read more...

Diagnostic Dilemma: The Case of the Missing Code

When doing mobile diagnostic work, no-code stalling complaints are a major part of your agenda. In most cases, the client shop is simply too busy to duplicate the failure or, in some cases, a long test drive will yield nothing in the way of useful...

Read more...

Secondary Ignition: The Art of Spark

What is a coil? From the beginning of the internal combustion engine, several different ignition systems have been used to create a high-energy spark. The most popular system, and the one that’s in use today, is a step-up coil. A coil is nothing...

Read more...

Diagnosing Catalytic Converter Failure Symptoms

Although construction can vary according to engine application, the common three-way catalytic converter contains a reduction and oxidation stage. To create maximum surface area, each stage is generally a ­ceramic or stainless steel honeycomb substrate...

Read more...

Home Brakes Measure Rotor Thickness, Runout: Stop Pulsation Comebacks Before They Start

Print Print Email Email
Let’s say a vehicle had .003” of lateral runout when measured at the outside face of the rotor. If this vehicle is riding on 205/55R16 tires, in one mile, the high-spot with .003” of runout goes past the caliper approximately 836 times. Over 6,000 miles, that spot on the rotor will go past the pads more than 5 million times. Every time this spot passes the pads, a little bit of the rotor’s material is removed. Over the course of those 5 million revolutions, enough material is removed to create a thickness variation that can be felt by the driver.
This is why it is critical to measure thickness and runout in a brake rotor and wheel flange even if new rotors are going to be installed.
Here are the recommended steps for measuring thickness and runout. These are the bare minimum steps you should be following for old and new rotors.

Before Starting
Mark the original position of the rotor with a paint or grease marker before removing the rotor.
Rotor Thickness
1. Inspect the rotor’s surface for defect, corrosion or cracks.
2. Find the discard measurements on the rotor. On some aftermarket rotors, they will be laser-etched into the sides of the plates. If a discard measurement can’t be found, look it up along with the specification for thickness variation or parallelism.
3. Using a micrometer, measure the thickness of the rotor in at least six spots that are opposite from each other.
4. Record the results. Variations in thickness should be between .001” and .003”.
Rotor Runout Measurement
1. Mount the dial indicator to a rigidly secure portion of the suspension, like the knuckle. Do not mount the arm to tie-rod ends or control arms. Position the indicator tip perpendicular to the rotor’s surface and 0.5” from the edge of the rotor.
2. Tighten down the rotor with the correct conical washers to the recommended lugnut specification.
3. Set the dial to zero and turn the rotor.
4. Mark the high and low spots of the runout. For most cars, the specification will be .002” or less.
5. Remove the rotor. Inspect the mounting surface inside the hat. Remove any corrosion or debris.

Runout in the Wheel Flange
1. Rotate the hub bearing assembly by hand. Any roughness, play or noise from the bearing is an indication of damage. Verify that the condition is normal or requires replacement.
2. The dial indicator base should be placed or clamped rigidly on a secure portion of the suspension. Position the indicator tip as perpendicular on the wheel flange as possible.
3. Set the dial indicator to zero. Next, turn the flange at least twice and observe the high and low spots of runout.
4. Mark the high and low spots of runout on the flange.
5. If the flange has more that .002”, or the readings are inconsistent, further corrective actions might need to be taken after rotor runout is measured.
Matching the Hub to the Rotor
By measuring and marking the high and low spots of runout in the hub and rotor, it is possible to match the high spot of runout in the hub with the low spot of runout in the rotor. This technique can be used to minimize the amount of material removed with an on-the-car brake lathe.
Flange runout can be corrected with tapered shims that are available to correct a runout of 0.003” (0.075 mm) to 0.009” (0.230 mm). A runout of more than 0.005”(0.125 mm) at the bearing flange cannot be corrected by the use of a shim. The combination of the rotor and bearing flange could prevent the rotor from being turned. Check the bearing flange runout after friction surface runout. Check flange runout by changing the rotor position 180º on the bearing. If the high spot changes 180º, the rotor could be OK or ready to turn after the bearing is shimmed.
Components should be marked as you perform an inspection of the assembly. Check the bearing endplay. Mark the relation of the rotor to the bearing flange. Mark the rotor high and low runout spots on the rotor friction surface. The low spot marked as zero and the high spot as 0.XX”. Mark the high and low runout spots on the bearing flange with the same method as the rotor friction surface.
Once you have collected the data, the following comparisons should be made:
• If the endplay exceeds manufacturer’s specifications, replace the bearing and recheck runout.
• Compare bearing flange to rotor runout position.
• If the shim cannot correct the runout, the bearing should be replaced.
• Check the rotor thickness. The minimum dimension should be stamped or cast into the rotor. There has to be enough thickness to cover the runout without going below the minimum thickness.
On-the-Car Runout Minimization
Today, you can purchase an on-the-car brake lathe that, after it has been attached to the vehicle, will automatically compensate for runout — quick and easy.
In some cases with excessive runout, a new rotor should be machined to match the vehicle, which helps to match the rotors to the hub flange.
Using an on-the-car lathe can help to reduce runout on new rotors. The main advantage of these lathes is that they are able to cut a rotor in its operating plane. This means that the rotor is machined to match the hub.
It has often been said that you should never machine new rotors, but what if the runout exceeds the manufacturer’s specifications when the new rotor is installed on the vehicle? This situation makes it permissible to machine a new rotor with an on-the-car brake lathe.
The following two tabs change content below.

Andrew Markel

Andrew Markel is an ASE Certified Technician and former service writer, and he brings this practical knowledge to the Brake & Front End team as editor.

Latest posts by Andrew Markel (see all)

Latest articles from our other sites:

Graywerks By ATP Automotive Exhaust Manifolds Include Hardware For Easy Installation

With vast coverage for both domestic and import applications and hardware included to make installation fast and easy, exhaust manifolds from Graywerks by ATP Automotive are the preferred choice of professional...More

WORLDPAC Opens Regional DC In Santa Cruz, California

WORLDPAC has announced the opening of a new regional distribution center in Santa Cruz, California. The facility offers expanded delivery and service options to local independent automotive repair professionals in...More

Saab: Fuel Sending Unit Replacement

The 2006 Saab 9-3 Sport sedan came in on the hook and the tow truck driver said, “I think it needs a fuel pump.” The gas gauge was reading less than a quarter of a tank and the low fuel warning light...More

Lithium: An Element That Is Charging Ahead

What is an EMV? As you read the hybrid and plug-in articles that my company, ACDC, is writing this year, we have coined a new term: EMV (electric motor vehicle). Rather than use hybrid, plug-in hybrid,...More

Pulling Codes: Multiple Misfire Personalities

A Story of Codes P0302, 04, 06, 08 & 03   This month’s diagnostic journey begins with a 2008 Land Rover Discovery that is taken in to a local testing facility for an emission test and...More

Snap-on Introduces New Software Upgrade 15.2

Keeping a technician’s diagnostic tool up-to-date is the only way a shop can ensure that they have the latest codes, tests, tips and data out of the box and miles down the road. With the new Snap-on...More

Ultimate Underhood: Chrysler Slant Six

While the Chrysler Slant Six did not have the raw power of the Hemi, it was just a sophisticated. The Slant Six went into production in 1960 and lasted until 1983. The 30º tilt was borrowed from Mercedes-Benz...More

Lithium: An Element That Is Charging Ahead

What is an EMV? As you read the hybrid and plug-in articles that my company, ACDC, is writing this year, we have coined a new term: EMV (electric motor vehicle). Rather than use hybrid, plug-in hybrid,...More