XPost: comp.mobile.android, misc.phone.mobile.iphone   
   From: xenolith@optusnet.com.au   
      
   On 14/5/2022 3:40 am, Andy Burnelli wrote:   
   > Xeno wrote:   
   >   
   >> Yeah, that's been the trend for quite some time now. Rotors are   
   >> considered as *disposable* as the pads themselves.   
   >   
   > Hi Xeno,   
   > (See the question in the bottom of the introductory explanation below.)   
   >   
   > A _lot_ of morons (like Steve) "claim" to need to replace rotors with every   
   > pad change, and even more morons opine that they simply replace rotors at   
   > every second pad change, and even more morons than those prevalent types,   
   > ask on the car forums the dumbest question possible, which is Q: *How do   
   > you know when to replace your rotors?*   
      
   I have often seen discs worn beyond limits by the end of the second set   
   of pads. When to replace? When they don't clean up on a lathe, are   
   undersized, or I use my judgement to assess that gouges, etc may cause   
   bed-in and braking balance issues. After you've done a few hundred, you   
   soon get a feel for what works ok and what doesn't.   
   >   
   > The reason all those three are the brain child of morons is that you   
   > replace a rotor when it no longer meets the spec, and, as you note below,   
   > the spec contains a few simple components, _all_ of which require tools.   
      
   And, because I was working *in the trade*, and later teaching my trade   
   in a college, I always had access to the required tools.   
   >   
   > Just as Dunning & Kruger wondered what made the bank robber think the lemon   
   > juice would work, and just as I wonder what makes iKooks believe their   
   > fabrications of functionality would work, I have wondered for years why   
   > people ask the dumbest "what oil" type of questions on car forums.   
   >   
   > Over the decades, I've realized the "what oil" questions and the when do I   
   > replace rotors questions are born of the exact same "Steve" mentality.   
   > 1. They don't know the spec, and, 2. They don't own the tools to   
   > _measure_ to the spec.   
   >   
   > It's really that simple, don't you think?   
   > Q: When do you replace rotors?   
   > A: When they no longer meet the spec.   
   >   
   > Q: On rotors, how do you know when they no longer meet the spec?   
   > A: You measure them.   
   >   
   > Q: What tools do you need to measure rotors?   
   > A: The most often missing tool is a dial gauge with a good sturdy mount.   
   >     The second most often missing tool is a simple one-inch mic.   
      
   A one inch mic is *useless* if it is of the standard form. You *need* a   
   disc micrometer whereby the bottom of the disc surface can also be   
   measured as well as near the periphery. After all, one of the checks   
   required is a *taper measurement*.   
      
   >     The third most often missing tool is a gouge depth and width gauge.   
      
   Again, I use the disc mic for depth but, whilst in the trade, I used my   
   own judgement.   
   >   
   > The tool I don't yet own is the latter (as I've never needed it).   
   > So I use a coin of the correct width but that's not the "right" tool.   
   >   
   > Q: What tool do _you_ use to measure the depth and width of a gouge?   
   > A: Xeno?   
      
   The brake disc micrometer designed for the purpose of course. But, as I   
   said in another post, with gouges I use my own judgement.   
   >   
   >>> There is one train of thought that turning sufficiently thick, flat,   
   >>> non-warped, rotors, is unnecessary and that after a short while the   
   >>> pads will break in to match the minor imperfections in the rotor,   
   >>> with just a little extra wear on the pads. "If your rotor surface is   
   >>> smooth there is   
   >   
   >> Indeed, I need to see a very overt issue before I would bother   
   >> machining rotors. If you don't feel the symptoms on a road test,   
   >> measurements look ok and the surfaces aren't gouged, I just fit pads,   
   >> then do a bed in process   
   >   
   > Given rotors cost about what it costs to machine them (and, in my last   
   > clutch replacement, flywheel machining was $60 while a brand new flywheel   
   > was only about $80), I have never bothered to have _my_ rotors machined.   
      
   That is what happens nowadays. Back in the day, some rotors were   
   damnably expensive - especially those integral with the hub. You had no   
   choice but to maximise their lifespan whenever possible.   
   >   
   > However, I've also never taken a car to a mechanic in my life for something   
   > as trivial as a four wheel brake job, which is just about the easiest job   
   > anyone can do at home if they have the most basic of the simplest of tools.   
   >   
   > The bed in process is critical in terms of what people call 'warp' (which   
   > is simply that the car does funny things, which I won't call 'shudder' or   
   > 'judder' or 'shimmy' or 'pulsations' since people call _everything_ "warp".   
   >   
   > However, that bed in process takes an appreciable amount of time,   
   > especially in areas like those where I live where the highway is nowhere   
   > near, and it's jam packed during all hours of the day with traffic.   
   >   
   > My question to you, Xeno, and to any others who get brakes done by the   
   > professional mechanics, is this simple but very important question:   
   >   
   > Q: Do professional mechanics take the car on a drive to do proper bedding?   
      
   Short answer, yes. Well, I used to! Not only was I taught to do that, I   
   saw the need.   
      
   --   
   Xeno   
      
      
   Nothing astonishes Noddy so much as common sense and plain dealing.   
          (with apologies to Ralph Waldo Emerson)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)