Rotor Runout and DTV: How to Decrease Comebacks with Two Simple Tools

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Rotor Runout and DTV: How to Decrease Comebacks with Two Simple Tools

Replacing rotors on every brake job is not a cost effective or efficient way to perform brake service. You may save 10 to 15 minutes by not having to use a dial indicator and a micrometer, but your chance for comebacks can dramatically increase.

Andrew Markel
By 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.
Published:
Replacing rotors on every brake job is not a cost effective or efficient way to perform brake service. You may save 10 to 15 minutes by not having to use a dial indicator and a micrometer, but your chance for comebacks can dramatically increase. 
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Even if you use new rotors, your chance of a pulsation comeback could be greater than it you left the old rotors on the vehicle. Runout in the hub and new rotor can stack up to cause Disc Thickness Variation (DTV) in a few thousand miles. DTV is the main cause of pulsation. 
  

sometimes rotor wear can be seen with the naked eye, but by this time the rotor is unsafe. if you can see a difference in plate thickness, it is a sign that the hardware and caliper needs replacement. rotor thickness should be measured in at least six areas of the rotor’s face. the dtv should not vary more than .001” in general. some manufacturers specify zero dtv.runout greater than .006” is a sign that the flange, rotor and/or bearing should be replaced. the needle of the dial indicator should be perpendicular to the rotor. measurements should be taken a quarter inch from the edge. first find the lowest point in the rotor and set the dial indicator to zero. rotate the rotor to find the high spot. this is the total indicated runout. mark the high and low spots on the rotor. before the rotor is removed, make sure you mark its position on the flange. if the runout is small, try repositioning the rotor 180º on the flange to cancel out the runout.the hub flange is ground zero for pulsation problems. any runout in the flange will be magnified by the rotor. before the flange is measured, most of the corrosion should be removed. do not use a wire wheel. this could damage the surface. some flanges and lug studs have anti-corrosion surface treatments that can be damaged by over aggressive abrasives. On some flanges, measuring runout is difficult due to a very small area that the needle of the dial indicator can ride on. Most manufacturers recommend taking the reading as far out from the center of the hub as possible. As a general rule, there should be less than .002” or below the manufacturer’s specification of lateral runout.

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Maximize Your Scan Tool

Are you maximizing your scan tools to their full potential? Don’t let them be just an expensive code reader.

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By Eric Garbe
Eric Garbe is a graduate of Columbus State Community College with a degree in Automotive Maintenance Technology. He has extensive independent and dealership field experience as a technician and shop owner and is an ASE Certified Master Technician and former Adjunct Automotive Professor. He has been professionally writing automotive technical articles and documents for many years and in his free time enjoys restoring old cars and creating custom interiors and upholstery.
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Scan Tool

If there’s a truth that extends across all computerized devices, it’s that we likely utilize only a fraction of the things they have the ability to do. Mobile phones are a great example. How many people do you know who only use them for calls, voicemail and text messages? We all know they do so much more.The scan tools we use every day fall into the same category. Are you maximizing yours to their full potential? Don’t let them be just an expensive code reader. That may be easier said than done, because it takes a lot of time to understand both the scan tool and how well it interacts with the vehicles you’re working on, but there are a few factors that can help you dive a little deeper into the functions at your fingertips.

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