XPost: alt.autos.toyota   
   From: rokigawa@NOSPAMtristarassociates.com   
      
   "SMS"  wrote in message   
   news:4abb0680$0$1588$742ec2ed@news.sonic.net...   
   > Ray O wrote:   
   >> "Jeff Strickland"  wrote in message   
   >> news:h9duqo$lrr$2@news.eternal-september.org...   
   >>> I'm confused.   
   >>>   
   >>> Once the rotors warp, they remain warped until they are machined or   
   >>> replaced. Warping is not a transient condition where the experience is   
   >>> on a mountain road but not on other roads. And, braking on a mountain   
   >>> road should be lighter and more evenly applied on a mountain road than   
   >>> in other places. The brakes might be used more often, but the braking   
   >>> ought not be "harder". It you are driving into a turn and mashing the   
   >>> brakes, your passengers are probably on the verge of puking.   
   >>>   
   >>> Having said that, slots and crossdrilling are done to help extract heat.   
   >>   
   >> Not quite.  The slots and cross drilling on the rotors allow the gases   
   >> that the pads generate when heated to escape more easily.  If the gas   
   >> can't be cleared from between the pad and rotor quickly enough, the   
   >> effect is kind of like an air hockey table, reducing the contact between   
   >> the pad and rotor and creating brake fade.  The slots in some pads serve   
   >> the same purpose.   
   >   
   > Obviously I can't see what's happening, but it feels like the brakes   
   > chattering against the rotors. I never notice it in normal freeway driving   
   > where the brakes are lightly used, but coming down a steep grade (like Old   
   > Priest Grade road near Yosemite) where the grade is up to 14% and engine   
   > braking isn't sufficient, I feel it.   
   >   
   > Supposedly this is referred to as disc thickness variation. "As the rotor   
   > gets hot, it is much more likely to increase thickness variation, thus   
   > increasing pedal pulsations as well as steering wheel and other vehicle   
   > vibrations." Of course I read this on a web site that also promotes   
   > Amsoil, so I don't know how true it is.   
      
   The disc thickness variation is what is causing the pulsation when the rotor   
   gets hot.   
      
   If engine braking is not sufficient, try dropping down one more gear range,   
   and instead of riding the brakes, try giving them a good stab to bleed off   
   speed, then let the speed build up a little, then give it another stab.  The   
   time between brake applications allows the rotors to cool a little.   
      
   I've driven on Old Priest Grade and also coming down Donner Pass.  The lower   
   gear range and stabbing the brakes works.   
   --   
      
   Ray O   
   (correct punctuation to reply)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)