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Why turn shiny brake rotors??

Discussion in 'The Garage' started by mofugly13, Mar 14, 2005.

  1. mofugly13

    mofugly13 1 ton bucket of rust Premium Member

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    I gave a set of rotors from my D44 to my girlfriend's friend. They were fine when I pulled them, but I was changing to drilled rotors. When I sent them over, they were as smooth and shiny as the day they came off my K5. She has a "mechanic" who does all the work on her '86 K5, and he said they needed to be turned before he installed them, or the pads would not seat properly. I would like to say he is full of $hit, but maybe he knows something I don't. I understand that is the case for flywheels when installing new clutches. But, his line of reasoning insinuates(sp?) that one would need to have their rotors turned every time a new set of pads was put on. I think you'd be approaching minimum thickness pretty quickly if that was the case. So, clue me in, am I free to tell him he's full of shinola?
     
  2. dark eternal

    dark eternal Registered Member

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    if they are warped at all...

    Ive gotton lots from the parts place warped even from sitting weird on the shelf I guess
     
  3. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    There are tons of fact, fiction, rumors, etc.... about new pads, rotors, and how you install and brake them in.

    If you can, turn the rotors when you put new pads on. Along with getting rid of warpage I think it provides a better 'feel' to the braking. I think new pads on a glossy surface require more pressure to get things stopped.

    Anyway, you will get a different answer for each person that post I bet... :D

    1 more thing - if you cant turn them burnish with orbital sander to take the glaze off.
     
  4. fatbob

    fatbob 1/2 ton status

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    I feel that they DO stop better after they have been turned, than they do when they are well worn. But I'm usualy too cheap and lazy to take em off and have them turned, unless they are grooved.
     
  5. beater_k20

    beater_k20 Banned

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    glazing. pretty much, with an old rotor you have a smooth slippery surface, and a freshly turned rotor has a smooth but rough finish. allows the pads to grab better.
     
  6. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    He's right. You take a set of rotors, run them with a set of pads, they are going to have a pattern to fit each other so to speak. You take the same rotors, hook them up with a different set of pads, the "pattern" isn't going to match and very possibly have a loss of performance. Turning them is no big deal.
     
  7. Fierospeeder

    Fierospeeder Banned

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    you dont need to cut the rotors if they are within specs. It just needs to be scuffed up a bit with a scotch or sandpaper pad. Same rules apply after cutting the rotors.
     
  8. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    :D :D :D
     
  9. mofugly13

    mofugly13 1 ton bucket of rust Premium Member

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    Guess I'll keep my mouth shut on this one then. But, WTF, how many of you take the hub off when you're doing brakes and take them to get turned? Sounds like it would turn a 20 minute brake job into a few hour affair. When I do my brakes, its , jack her up, remove the wheel, remove the caliper, remove old pads, reset the piston, new pads in, caliper back on, wheel back on. Very quick and simple. I have even put new pads on a slightly grooved rotor and noticed the next time I changed pads that the groove was, in effect, turned down so the rotor was smooth again. I donno. I'm sure that freshly turned rotors stop better than smooth ones, but I have never had brake problems, and I have never had my rotors turned. How many miles do you really go on a freshly turned rotor before it is worn as smooth as it was before it was turned, anyway? Also, wouldn't semi-metallic pads cut through the "glaze" anyway? Excuse my ignorance, but I thought rotor and drum turning was for fixing warped, grooved, and runout problems.
     
    Last edited: Mar 14, 2005
  10. Triaged

    Triaged 1/2 ton status

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    Hate to tell you this but most of you guys are wrong. Smooth rotors stop better. GM recomends NOT TURNING them unless they are warped or groved. If you could get the rotor to a glass smooth surface that would be best.

    Edit:
    That said it isn't a bad idea to turn rotors once they are put on the hubs to make sure there is no runnout. But you could check that without turning them.
     
  11. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    I haven't had rotors turned in over 10 years. If they're warped or bad in anyway I found it easier to buy new ones. For the cost of having them turned down twice you could buy new ones. JMO :xmas:
     
  12. Fierospeeder

    Fierospeeder Banned

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    In general, it is recommended not to cut rotors.

    only time to cut rotors
    1. grooves deeper then .060 in
    2. parallelism/runout
    3 badly rusted
     
  13. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    A brake rotor or brake drum should be machined EVERY time the brake pads or shoes are replaced. There are a couple reasons for it, first is to get rid of the glaze (shine), second is to make sure they are true without any runout, and third is to make sure both sides are paralell to one another. They ALWAYS must be machined if they are removed from the hub and then reattached to either the same hub or a different hub because now they need to be made true to the new center, (which is the bearing races in the hub to which the rotor is attached).

    If you never machine your rotors or drums when you change pads or shoes the only thing you accomplish is a pedal that doesn't go as far to the floor, you will not increase the stopping power one single bit since the rotors or drums have a glazed surface which will glaze the pads or shoes as well.
     
  14. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    Here we go..... Told Ya ;):D
     
  15. Fierospeeder

    Fierospeeder Banned

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    Are you saying my 500 page book that is all about brakes is wrong? :blush:
     
  16. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    And I could probably pull out a 500 page book all about brakes that says you are wrong.

    But that is okay, after a visit to StripperWeb.com last night, I feel secure in knowing that I may not bring the biggest piece of meat to the table, yet even a large contigent of strippers who are Internet savvy prefer the tactics of the gunbattle over the size of the weapons involved........................ :D
     
  17. Fierospeeder

    Fierospeeder Banned

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    i doubt you can find a book that says otherwise.

    It is well known in the business, if a rotor should be cut or not.
     
  18. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    Ah hell, let me go get it...................................... :D
     
  19. Fierospeeder

    Fierospeeder Banned

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  20. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    Okay boys and girls, guys and gals and Canmore.................................. :D

    Here's the source material from which I have pulled the following quote: "Automotive Service, Inspection, Maintenance, Repair" authored by one Mr. Tim Gilles, published by Delmar in the year of our donut, 1999. This was purchased brand new by yours truly when he underwent one year of automotive service training at a local JC where I resided at the time.

    The book weighs in at a hefty 1196 pages and even has pictures. :D

    This quote is printed on page 722, Chapter 52, Brake Service:

    "When drum or disk linings are replaced, it is COMMON practice to resurface (turn) the drums or rotors using a drum or brake lathe (Figure 52.33). "

    Now with that being said, not only does the book say it, but the instructor I had for that particular block of instruction, a 20 year vet of GM, who came at the recommendation of the smartest and best mechanic I've ever known, my father-in-law; but turning rotors and drums in the two shops I worked in when pads/shoes were replaced were not common practice, but it was mandatory.
     

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