XPost: comp.mobile.android, misc.phone.mobile.iphone   
   From: scharf.steven@geemail.com   
      
   On 5/9/2022 5:17 PM, Xeno wrote:   
   > On 10/5/2022 1:39 am, Andy Burnelli wrote:   
   >> Xeno wrote:   
   >>   
   >>>> You can't test warp on the vehicle (not reliably anyway).   
   >>>> It has to be tested on a known flat bench (or using known flat tools).   
   >>>   
   >>> Or mounted on a brake lathe   
   >>   
   >> Agreed. All you need is a long flat edge and feeler gauges as a minimum.   
   >   
   > Dial indicator with the disc mounted on a brake lathe is my choice. Much   
   > more accurate and allows you to ascertain exactly where the runout is   
   > and enables the mechanic to differentiate between such things at   
   > thickness variation, taper, hard spots and warp. A long flat edge and   
   > feeler gauges isn't going to get you there. What you also need, in   
   > particular for assessing thickness variation and taper, is a disc   
   > micrometer;   
      
   In the early days of disc brakes, the rotors were heavy and thick and   
   could be resurfaced multiple times. Brake jobs were pretty inexpensive   
   since rotors didn't need to be replaced, they were dropped onto a lathe.   
   Back when I did my own brake jobs I would take the rotors to my   
   brother-in-law's shop and he would resurface them for me, but you could   
   also get a machine shop to resurface them for $10 each.   
      
   But the mass of thick rotors negatively affected fuel economy so much   
   thinner rotors began to be used, and they usually can't be resurfaced   
   even once, they have to be replaced at the same time the brake pads are   
   replaced. They also warp much easier. It also actually became not that   
   uncommon to replace warped rotors, but not the pads, since the pads were   
   fine.   
      
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