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

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Engine Compartment

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 the director of content for Underhood Service magazine. He has been with Babcox Media for 20 years. He is a technician and former service writer and holds several automotive certifications from ASE and ­aftermarket manufacturers.
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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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