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Using Sandpaper to Roughen up Brake Rotors

Discussion in 'General' started by ben315vz, Apr 29, 2012.

  1. ben315vz

    ben315vz Donating Member

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    A while ago in another thread (can't remember which one), I got flamed because I said that sometimes I roughen up brake rotors with sandpaper instead of machining them.

    I just found post on another forum that I found quite interesting. Please read it, and discuss.

    Resurfacing Brake Rotors

    Since I am constantly reading posts where this question is asked I thought I would make a post devoted to it.

    DO NOT resurface brake rotors just because you are replacing the pads. There is absolutely no reason. You shorten the rotor life, make it thinner so it does not hand the heat as well and spend money you should not be spending.
    Almost every auto manufacturer has now come out and confimed that all of thier dealers should not be resurfacing rotors when brakes are done. It is only done to make money for the dealer.

    Reasons for a rotor to be resurfaced.
    1. Parallelism. The rotor is not true as it relates to the hub when it is on the vehicle. This is why they all recommend on car resurfacing.
    2. Rotor scoring due to poor pad formulation, etc. Even then, GM's recommendation is to check the depth with a penny and if you can still see the top of Lincolns head then they are okay (believe it or not!)


    If you would like to remove old pad transfer material from a rotor surface then you can use a 120 grit sandpaper to scuff up the surface. Excess pad transfer buildup can be removed without resurfacing. Many times it can be done by rebedding the pads. Roll-loc discs is also an option to clean up the surface of a rotor for pad transfer but even then I would go with a red (aluminum) disk, browns are just a bit to heavy.

    I can honestly say that in the last 15 years I have never resurfaced a rotor on any of my 7 or so cars from all different manufacturers. Reason? Wheels should always be torqued with a torque wrench with no exceptions. I worked in a dealership for years and NO I didn't use one on customer cars because A) thatisn't the fast way when your flat rate B) If they start to pulsate I can just cut or replace them later (not my money but I make money doing it)
    That is just the way it is. Don't think for a second that wheels get properly torqued at a dealership. Torque sticks only worked in a controlled situation in which the impact gun only puts out 250 ft lbs of torque. I've seen sticks broken by Impact guns because they are capable of a lot more then 250!

    If you must have the wheels removed by a delaer or anyshop for that matter, request they use a torque wrench to reinstall the lugs and then when you get home, loosen all the lugs and retorque anyway.
     
  2. 383 hatch

    383 hatch Well-Known Member

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    At work, we never, ever machine rotors. We do 1 of 2 things. If the rotors are not pulsating, grooved/scored or undersized, we just put pads in and leave it at that. If the rotors are stuffed, we just whack new ones on. It seriously isn't worth machining rotors these days (that's also because we are an hour away from the nearest place that can machine rotors which means too much down time). Having said all that, we've never used sandpaper on rotors, because there is no need.
     
  3. showbags

    showbags SENIOR EL'BAGO

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    ^^^^ + 1. For the price you can buy rotors for now, why bother machining. Throw those mother f#%\ers in the bin and put new ones on.
     
  4. ben315vz

    ben315vz Donating Member

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    Where I work, I have no choice. I have to do what I am told, so if the boss says to machine the rotors, they have to be machined. If he wants me to just roughen them up with sandpaper, then thats what has to be done.

    They get good prices on rotors from Repco anyway, I would rather pay the extra to get new rotors.
     
  5. Darren_L

    Darren_L Well-Known Member

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    the only time you need to machine rotors is when they have excess lateral runout or there is excess surface wear/lips on the edges etc.

    Otherwise, if the rotors are in good condition and you are just carrying out a routine pad change, nothing wrong at all with just roughing up the rotor surface with some sandpaper to aid brake pad bed-in.
     
    Last edited: Apr 29, 2012
  6. 1SIKR8

    1SIKR8 New Member

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    try pricing rotors on the HSV's with the premium brake upgrade, not cheap even if going aftermarket

    deafinatly a good read scvs6
     
  7. showbags

    showbags SENIOR EL'BAGO

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    Yeh, that's a different story of course. I was really referring to the likes of DR40's & 41's.
     
  8. ben315vz

    ben315vz Donating Member

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    There is a 2007 FPV BF MKII GT that comes in to work all the time for servicing, we have already had to replace the brake pads twice and the rotors were so worn out that they had to be replaced as well. You could tell because the slots were almost gone. We ended up buying aftermarket drilled and slotted rotors and brake pads (both times) but they were still expensive.

    There is also a customer that owns a FPV BF Force 8, I have never worked on that car myself but I am pretty sure that the brakes and rotors have been replaced a couple of times (at least once). Genuine was too expensive.
     
  9. ben315vz

    ben315vz Donating Member

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  10. Darren_L

    Darren_L Well-Known Member

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    well that's certainly different...
    I like how someone actually claims it's 'dangerous'.... I'd like to know how ?
     
  11. Jxfwsf

    Jxfwsf Well-Known Member

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    As above, if the rotor is warped, have excessive run out or deep grooves then it's either machine or replace.
    Problem these days is that rotors general don't have enough meat left on the bone to be machined by the time they get to this stage, machining would result in being below minimum thickness.
    Once again as mentioned above, roughing up the surface to aid new pads to bed in isn't a bad thing to do, although unneeded.
     
  12. ben315vz

    ben315vz Donating Member

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    Yeah thats why I thought. I was trying to help and then was told that it's dangerous. The place where I work has been doing it for 43 year and have never had a problem.
     
  13. Jxfwsf

    Jxfwsf Well-Known Member

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    no more dangerous than leaving the car for a week in a humid environment and the rotors get a decent layer of surface rust.
     
    Last edited: Apr 29, 2012
  14. ben315vz

    ben315vz Donating Member

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    I have been to car yards and all the rotors are rusted up from the car just sitting there waiting to be sold haha.
     
  15. 1SIKR8

    1SIKR8 New Member

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    i got a bad habbit of washing the R8 then putting it in the shed, go to take it for a drive a couple of weeks later to find the front rotors have seized to the pads, the shed has 2 black marks from backing up till they let go, by god the first time it happened i nearly cried haha now after washing it i steal the ol girls hair drier and dry the brakes, works a treat haha
     
  16. ari666

    ari666 250,000 hits

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    My local brake shop is a 15 minute drive and charges me 10 bucks per rotor

    Average price fir new rotors for an import is around 120 on the pair IF you can get them. Evo rotors were 900 for a pair.

    But yeah 40 bucks to lose a bit of material or 1500 for new rotors all round you can safely bet that im going for a drive to the brake center.
     
  17. ben315vz

    ben315vz Donating Member

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    But what that guy was saying is that you don't need to machine brake rotors, you can just replace the pads and leave it at that. You can roughen the rotors up with sandpaper if necessary.

    I also know what he is saying with the wheel studs breaking sometimes if done up with an impact gun, I have seen it happen at work a few times. I would prefer doing up every bolt/nut to the correct torque setting, but I also understand that if you are busy, then there is no time.
     
  18. VS_Pete

    VS_Pete Donating Member

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    Good read thanks.

    PS. Where do I find out the correct torque setting for thr VS/VE cars.
     
    Last edited: Apr 30, 2012
  19. ari666

    ari666 250,000 hits

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    i have used the rattle gun for nearly 15 years and NEVER had a wheel stud break. the rotors thing very much depends on the car. i can tell you every car i have needed to change pads on has needed a machine.


    i have been known to use a flat file on the contact surface before :p ive always been taught that pads need to 'bed in' and they need some cross hatching to get that process happening quicker.
     
  20. Darren_L

    Darren_L Well-Known Member

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    I've never seen a rattle gun break wheel studs (although I have no doubt some rattle guns are capable of it). However I have seen plenty of wheel studs stretched to shithouse by overzealous rattle gun operators - to the point where the wheel nut is too tight to wind on by fingers.

    When I was in the trade, I had my rattle gun torque setting adjusted so that it would rattle the nuts up to just under the correct torque setting. Then I'd run around with a torque wrench, usually less than half a turn so they were torqued correctly.
     

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