Brake Rotor Machining

Discussion in 'General Motoring' started by John Gregory, Jun 17, 2005.

  1. John Gregory

    John Gregory Guest

    The factory manual for my 2000 Concorde LXi states: "...the rotor should be
    resurfaced using a hub-mounted on-car brake lathe..." This implies that the
    dealership rather than the owner is going to do this job... or do brake
    shops and service stations usually have this machine now? Apparently it's
    not recommended that the discs be turned on a bench. What can happen that
    could go so wrong if the machining were done to spec?
    John Gregory, Jun 17, 2005
  2. If the rotor is not grooved and is not warped and it still
    exceeding the maximum thickness, then change the pads and leave it be. If
    it is
    damaged, throw it out and buy a new one.

    Ted Mittelstaedt, Jun 17, 2005
  3. John Gregory

    MoPar Man Guest

    I asked a lot of service garages the question of on-hub vs on-bench
    turning of brake rotors. The consensus is that if the rotors are not
    integral with hubs (ie if they just slide off the lug bolts) then they
    are taken off and turned on a bench.

    Apparently some european rotors can't be taken off and are then turned
    on wheel-mounted lathe (which is more expensive).

    I think that wheel-mounted lathes are not exactly rare.

    What is happening is that (as I found) Chrysler wants to sell you on a
    more expensive proceedure rather than the $10 or $20 per rotor to have
    them turned on a bench.

    They would rather have you buy new rotors, but if you're insistent
    they will turn them, but in your case they're rather use the most
    expensive method.

    I brought my rotors to (oh I forget where) and had them bench-turned
    last fall for my '2000 300M. I had quite a lot of pedal pulsing and
    steering-wheel-shimmy that completely disappeared after turning the
    front rotors. I'm positive that the rotors weren't warped - but that
    the pulsing and shimmy were caused by surface pitting.

    Dealerships use rotors are a scam, and many people have been "trained"
    by the dealers to thow the rotors out and buy new instead of turning
    them. I think surface pitting is probably the cause of most rotor
    problems these days (cars are lighter then they used to be and hence
    warping is more rare, and warping caused by over-tightening the lug
    nuts is an urban legend these days).
    MoPar Man, Jun 17, 2005
  4. John Gregory

    TNKEV Guest

    same price for either here $130(wich is high IMO)

    We have and use one.

    At our price purchasing new rotors is sometimes cheaper.

    I have not been "trained"in this manner.
    rotors have to be measured here and the measurements written on the R.O.and
    initialed by the shop foreman.
    TNKEV, Jun 17, 2005
  5. John Gregory

    David Guest

    It is faster and easier to mount the hub mounted barake lathe then to take
    off the rotors bring to the bench mount them, then take off and re-mount on
    the car. Just bolt the hub mounted lathe and it is done in less time.
    David, Jun 17, 2005
  6. John Gregory

    John Gregory Guest

    This brings up another point where experience would come in hand; the
    condition of the rotor. The manual says "If the rotor surface is deeply
    scored or warped..." ... but I don't know what to make of what I observed. I
    found the rear rotor smooth when I ran my fingernail across the surface (but
    I didn't repeat that anywhere else on the rotor. That leaves a lot of
    surface unexplored.) The front rotor proved different, however. I didn't
    find a "deeply scored" surface but I did find what seemed to be a few hair
    line beads around mid way into the surface that could be sensed by my
    fingernail. These weren't groves. They felt like very small bands raised
    ever so slightly higher than the main surface. The brakes don't squeak but I
    do feel a slight pulse at the very end of a brake session when the car is
    braked from high speed. At lower speed when I feather the brake to stop
    easily, I get nothing. I've been told by one mechanic that "if it pulses at
    all, the rotor is warped. Replace it." I've since found that man's
    credibility at stake; he also told me his shop doesn't use the hub-mounted
    on-car brake lathe because "it costs too much in time and labor to hook all
    that up."

    Q1) Any comments about the pulsations?
    Q2) When I do this job next week, maybe I can take the rotors in question to
    my Chrysler dealer and let them look at them. Would they be able to tell? I
    trust the guy I deal with... for the most part. :)
    John Gregory, Jun 17, 2005
  7. John Gregory

    Bill Putney Guest

    The more I mess with brakes, the more I'm convinced that what we call
    warped rotors often is not that at all. It's a knee-jerk response any
    time we get vibrating brakes. One possibility is inconsistent pad
    filming (that can change with hot brake application) - could explain
    what you're seeing. I've just about concluded that pads can be as or
    more important than rotors in preventing vibration (the filming thing).

    Not to sound like a commercial, but I had problems on my last set with
    Akebono ceramics. I can't prove it, but I think the pads were filming
    horribly. When I got new rotors, I changed the pads to Performance
    Friction's Z-Rated™ pads at the strong insistence of the rotor
    manufacturer (their engineer said that they have had a lot of rotors
    returned due to vibration problems only to find that certain ceramics
    were filming them and causing the problem). Anyway - My '99 Concorde
    brakes have been razor smooth for the longest period of time since I've
    had the car since making that change.

    Bill Putney
    (To reply by e-mail, replace the last letter of the alphabet in my
    adddress with the letter 'x')
    Bill Putney, Jun 17, 2005
  8. John Gregory

    tim bur Guest

    the dealer i work at sold the on the car lathe it was a waste of money
    if i find any rust pitting on a rotor it replaced with new, like cancer
    you can't stop rust and it only gets larger and it is a issue not to over
    torq. the wheel lugs because the hub metal is thinner these days
    tim bur, Jun 18, 2005
  9. John Gregory

    MoPar Man Guest

    I think you meant "said" when you wrote "sold" (above).

    It may be a waste of money (or, it _is_ a waste of money), but is it
    necessary for removable rotors, is it faster, or is it a "premium"
    service option designed to make the customer throw in the towel and
    say yes to new rotors?
    Do you ask the customer first? Do you tell them that turning the
    rotors will probably get rid of the pitting? Or is it easier for you
    to not get your hands dirty and pull a new set from the parts dept.
    and let the customer pay $350 for the whole job instead of $40 to turn
    the rotors?
    Rust will start on the new ones the minute you get the job done and
    you take the customer's car to the wash bay to give the car a wash
    before you hand the keys over.

    Turning the old rotors will get rid of practically all the pits and
    give you a surface equivalent to new rotors.
    You'll break an alloy wheel (or strip a lug) before you apply enough
    torque to distort a hub. You will not distort 2 inches of solid steel
    by over-tightening a lug nut.
    MoPar Man, Jun 18, 2005
  10. John Gregory

    pottsy Guest


    Just replace the rotors instead. Here in Blighty, getting the rotors turned
    costs about £10 and new ones are about £20-£30, (pt cruiser, ford granada
    and the jag) factor in the added downtime, needing another car or a friend
    to take the things to an engineering shop and then fetch them back again and
    the new ones can work out cheaper.
    A problem I've had with vented discs before is that the cooling vanes down
    the centre of the rotors can crack and cause different expansion rates along
    the disc, which will run true when tested cold but then warp when hot, and
    cracks are regarded as 'a bad thing'
    Also, when trying to stop nearly two tons of car from three figure speeds, I
    want the things to work, more metal = more cooling = less fade

    pottsy, Jun 18, 2005
  11. John Gregory

    Guest Guest

    I think he said he sold it because it was a waste of money. And I
    have to disagree about not being able to warp rotors by mis-torquing a
    wheel. It is a VERY common problem on some makes and models - wheel
    lugs SHOULD be accurately torqued, not just slammed on with the impact
    cranked right up.
    Guest, Jun 18, 2005
  12. John Gregory

    KWS Guest

    My experience with rotors (especially on the '96 T&C) is that they seem to
    warp when new. That's not always true, as the set on the car right now have
    been OK. Once they warp and I get them turned, they don't seem to warp

    I don't have a good explanation for this. It's almost luck of the draw. I
    have always used a torque wrench, criss cross pattern, tightened in steps,
    etc. When all is said and done, this seems to have no effect whatsoever on
    if they will warp or not (at least on the Chrysler).

    So I agree with the poster who poo-pooed the holy ritual of carefully
    torquing the lugs. All it seems to do is make you feel righteous.

    KWS, Jun 24, 2005
  13. John Gregory

    Mark Guest

    My '97 has always had warped rotors. I finally bought a dial indicator and
    base & did some further investigation. I always thought both sides were
    toast. It turns out in this case only one side was out- and this particular
    (new) $50 rotor was not warped but was out thickness wise. I bought two new
    rotors, one was a Raybestos PG+ (same as the shot one) and the other was a
    Chinese made off brand for $17. I put the cheapy on as a guinea pig - its
    been doing fine for over 5k miles now. I kept the PG+ as a spare along with
    the NEW PG+ with the thickness prob. Before uncovering the thickness issue,
    I also used a 3M Roloc on a die grinder to get rid of the oxidation on the
    alloy rim to rotor mating surfaces.

    I've owned a plenty of cars,trucks and vans with disc brakes - this is the
    only one so far that has such delicate, sensitive brakes requiring
    calibrated tourque wrenches and apparently on the vehicle turning equipment.
    Drum brake wise, my '69 dart is another matter ;-)

    Bottom line : Get a dial indicator + base & diagnose what is really going
    on. This really sheds a bight light on the issue. (Harbor Freight has a
    magnetic base & arm on sale for around $8 - they also have cheapy dial

    Mark, Jun 24, 2005
  14. John Gregory

    Bill Putney Guest

    Excellent point, Mark.

    If more people aware of using dial indicators to actually measure runout
    on a brake rotor, there wouldn't be such a vacuum of knowledge on the
    various forums as to actual root cause of brake vibration (i.e., to rule
    in or out rotor warping) on specific platforms. I was aware of using
    them, and in fact have borrowed them over the years from my employer at
    the time, just never in later years (for my LH car). The other problem
    is that people are not into putting the effort into the attention to
    detail and time it takes to make the runout measurement - even if they
    were in everybody's DIY garage.

    I would love to take my previous pair of front rotors and have them
    thoroughly analyzed to determine if:
    (1) One or both are or are not warped,
    (2) One or both have thickness variation,
    (3) And/or there was a non-uniform filming issue with the particular
    pads as I suspect.

    Bill Putney
    (To reply by e-mail, replace the last letter of the alphabet in my
    adddress with the letter 'x')
    Bill Putney, Jun 24, 2005
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