XPost: comp.mobile.android, misc.phone.mobile.iphone   
   From: xenolith@optusnet.com.au   
      
   On 9/5/2022 7:15 pm, Andy Burnelli wrote:   
   > Xeno wrote:   
   >   
   >>> Regarding brake rotor warp (as in "potato chip"), that (almost) never   
   >>> happens on rotors that didn't come out of the factory already warped.   
   >>   
   >> When I was doing a lot of brake repairs, and operating a brake lathe,   
   >> I came across many warped rotors.   
   >   
   > Remember, warp (as in potato chip) is _different_ from runout.   
   > Warp will cause runout but so will a lot of other things cause runout.   
   >   
   >> One is required, after all, to check discs and drums for wear,   
   >> distortion, runout and the like.   
   >   
   > Let's take those items one by one:   
   > a. wear   
   > b. distortion   
   > c. runout   
   > d. And the like   
   >   
   > Which one of those are you considering "warp" because if you say "all of   
   > them" then you're saying everything _is_ warp, and I'm not saying that.   
   >   
   > I'm saying warp is something very specific, and it's _not_ runout (which is   
   > something else altogether), and neither is it wear.   
   >   
   > I don't know what you mean by "distortion" but that's the closest term you   
   > used to what is warp (as in potato chip).   
   >   
   > Warp is checked against known a flat surface, as you're well aware, where   
   > warp, the way I'm using it, means one side (at least) of the rotor is not   
   > laying flat on the test bench (the other side may or may not be parallel as   
   > that's even worse if it's not equivalent).   
   >   
   > We should assume solid rotors for simplicity, but I understand that common   
   > vehicular rotors often have two discs separated by fins so there are a few   
   > measurements we can make against a flat bench surface to measure warp.   
   >   
   >> In my experience, there were two possible factors involved in warped   
   >> discs - overheating of rotors and incorrect sequence tightening of   
   >> wheel nuts.   
   >   
   > Warp (as in potato chip) will certainly cause runout but runout itself   
   > isn't warp.   
   >   
   >> Or simply overtightening.   
   >   
   > Runout isn't warp.   
   >   
   >> And, no, they didn't come out of the factory already warped.   
   >   
   > I only bring that up because morons always try to find holes in my   
   > scientifically based arguments and that's one of the holes they are   
   > desperate to find.   
   >   
   >> The worst for warping through overtightening were the integral hub and   
   >> disc rotor.   
   >   
   > Runout isn't warp.   
   >   
   > And besides, the simplest cure for what people "call" warp often is a   
   > rebedding procedure which has _zero_ effect on the bolt torque and zero   
   > effect on runout.   
   >   
   >> The separate rotor tended to be more prone to warping through   
   >> overheating.   
   >   
   > Warp almost never happens and anyone who says it did never mesaured it.   
   > Not even you Xeno.   
   > Nobody does (except people who _understand_ what warp is, as in potato   
   > chip).   
   >   
   > 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   
   >   
   >> Note too, a warped disc will evince different symptoms to a disc   
   >> suffering pad deposition. \\   
   >   
   > Holy Shit. Of course. A truly warped rotor (as in potato chip) is fucked up   
   > beyond belief. No amount of pad rebedding will solve a warped rotor (as in   
   > potato chip).   
      
   I wasn't saying anything about rebedding at all.   
   >   
   > Almost nobody could machine a warped rotor (as in potato chip) back to   
   > perfection simply because the amount of metal needed isn't going to be   
      
   Depends on the amount of warp and whether the rotor still meets minimum   
   specs afterwards. It only takes a very small amount of warp for the   
   driver to be able to sense it.   
      
   > there if the warp (as in potato chip) is appreciable.   
   >> The first car I owned that suffered from disc warping was a MkII 240   
   >> Ford Cortina but I drove that thing like a rally car back in the days.   
   >   
   > I'm going to have to call bullshit on the warp (as in potato chip) since   
   > there is zero chance that you measured it (using the proper tools for warp,   
   > which, as you well know, requires a known straight tool).   
      
   The car showed *symptoms* of warp, the rotors, when measured showed   
   *evidence* of warp. I drove the car, I felt the symptoms, I measured the   
   rotor warp.   
   >   
   >>>   
   >>> Regarding temperatures, the _melting_ point is (almost) impossible to   
   >>> reach   
   >>> in braking operations given the type of vehicles we're all talking   
   >>> about.   
   >>   
   >> I managed to reach it on one car I owned back in the early days of   
   >> disc brakes. Admittedly, the rotor was sub par on the thickness hence   
   >> a reduced heat capacity. It sure melted at the periphery though and   
   >> was showing signs of heat stress all over - it was black and blue.  ;-)   
   >   
   > I doubt it. Rotors are made of a variety of steels (e.g., motorcycle rotors   
      
   I don't, I saw the evidence.   
      
   > are often stainless steel) but even for the worst quality cast iron rotors,   
   > look up the temperature it takes to melt them.   
      
   Automotive rotors were pretty much all cast iron back in the era   
   concerned. And the rotor did *melt* at the periphery, as I stated. It   
   had been damn hot all over but the periphery was clearly melted.   
      
   > I'm not saying it's impossible. But I doubt it happens for normal passenger   
   > vehicles (I'm not talking space shuttle stuff or fighter plane stuff).   
      
   Nor am I. I wasn't and never have been an aviation mechanic.   
   >   
   > Look it up.   
      
   No need, I saw the evidence directly.   
   >   
   >> Who remembers actual numbers from a couple of decades or more back? I   
   >> used to measure runout, thickness variation, taper, etc, compare to   
   >> specs, then machine.   
   >   
   > Yes. I know. But did you measure warp (as in potato chip)?   
      
   Yes, I did, with a dial indicator. Definitely warp.   
   >   
   > You can't measure warp without a known straight surface to compare against.   
   > A mic won't measure warp.   
   > A dial gauge won't measure warp (unless it's a special setup).   
      
   It was a special setup - a brake lathe. Runout and warp shows up very   
   clearly when the hub and rotor assembly is correctly mounted.   
   >   
   > HINT: I've never seen anyone who did who said their rotors warped when what   
   > really happened was something else (e.g., runout or pad deposition).   
      
   Depending on the site, runout can be a symptom of warp. You verify it as   
   warp by checking both sides.   
   >   
   >> If they wouldn't clean up and still remain within specs, they would be   
   >> replaced, and that could be determined from the measurements.   
   >   
   > I seriously doubt an actual warp (as in potato chip) could be machined, but   
   > if it's only slight, then maybe, but what fool would want rotors that were   
   > actually warped (as in potato chip) even after they were machined?   
      
   Well, these days the rule is discard and renew, don't machine.   
   Procedures have changed.   
   >   
   >> This was my preferred brake lathe;   
   >> https://www.ammcobrake.com/ammco-brake-lathe-model-4000b   
      
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