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  #1  
Old 09-01-2002, 07:12 PM
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Brake life / pads / rotors

How long does the rotor last based on sets of pads? This would be based on the stock parts from Subaru. How many sets of pads can be replaced before the rotors need to be replaced? Assuming of course that the pads do not dig into the rotor.

Thanks
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  #2  
Old 09-01-2002, 08:23 PM
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this would be kinda hard to answer, considering everyone drives (and applies brakes) differently. YRMV (your rotors may vary)
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  #3  
Old 09-01-2002, 09:52 PM
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Actually, it's a pretty legitimate question. Driver A. slams 'em on at every light, Driver B. gently applies brakes & coasts to lights.
Driver A. replaces front pads at 30K. Driver B. replaces at 70K. Logic tells me rotor wear must in proportion to the pad wear. Driver A.'s rotors will be worn thinner, quicker than Driver B.'s.

Ron.
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  #4  
Old 09-01-2002, 10:03 PM
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Rotor wear or Rotor Warp

I would suggest that the driver that takes it easy would get MUCH more life out of rotors because they are less likely to warp. By the way my ART's are doing very well.
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  #5  
Old 09-01-2002, 10:15 PM
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My observations from the field generally result in three sets of pads to one pair of rotors (front) for all cars. If you drive like a ...hmmm...what's that show on MTV? Oh yeah, jackass - anyway, you will not only have a greater chance of warping the rotors but you can also blister them and cause their premature replacement.
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  #6  
Old 09-01-2002, 11:23 PM
MoreIBNR MoreIBNR is offline
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That's going to depend on several factors, primary ones being: are you resurfacing at every pad change and what pads you use. The harder the pad material, the more of the rotor that will wear.

Generally I find you can resurface the rotors once, maybe twice, so that would be 2 or 3 pad changes.

Oh, it also depends on who does the resurfacing - some shops don't want to spend any time and dial down the lathe to do it all in one pass, taking off a lot of metal to make sure it only takes one pass (count on only one resurfacing with this type of shop), others will only take off a couple of thousandths at a time, requiring 2 or 3 passes, but leaving the max thickness. You may get 2 resurfacings this way, depending on how true they wear.
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  #7  
Old 09-02-2002, 01:54 AM
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Re surfacing Rotors

I will say this once on the basis of proven practical racing experience and once only and am not prepared to enter into any futile argument.

Provided radial scoring is not excessive and is laterally true and braking prior to pad replacement has been smooth, removal of metal from a rotor is not required. New pads will bed in on the true corrogated surface without a problem or effect on braking performance.

However a shop can show the surface to the customer aptly described as requiring immediate extra expenditure. What is more grinding will bring the customer much closer to the point of having to hand over more money for replacement rotors and this is good business. Furthermore it wiil only be a short time before the scoring is again apparent and the process can be repeated.
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Old 09-02-2002, 06:24 AM
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Well said Trevor
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  #9  
Old 09-02-2002, 07:45 AM
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In fact most major OEMs are now recommending against resurfacing the rotors. GM goes as far as to state that a .060" deep groove is acceptable, which is odd because the old standard was to not remove more than .030" from each face. I try to test drive each car that comes in for a brake check and if it isn't vibrating I don't cut them.
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Old 09-02-2002, 09:51 AM
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This is all consistent with what Bendix posts on their website - resurfacing is not necessary as long as they are not warped and lateral run-out does not exceed a certain limit (which I don't remember what that is).

Question is, how do I check the lateral run-out?
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  #11  
Old 09-02-2002, 02:19 PM
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Lateral Run Out

Lateral run out is tested with a dial indicator and magnetic or clamp style mount. Mount the dial indicator so that it follows the surface of the rotor to check to see if the rotor is warped.

I turn rotors with every brake job I do for a customer. Mostly to avoid any future problems, comebacks. On my own vehicle it may depend on my mood.
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  #12  
Old 09-02-2002, 02:30 PM
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Beav, If the manufactures are backing it up then there are no worries. But as a Tech and especially a teacher I was always concerned about lawsuits and such.

Do you think the current trend is that manufactures are going to "on the car lathes"? I know that Ford GM and Chrysler all have at least some vehicles that require this type of service.
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  #13  
Old 09-02-2002, 05:09 PM
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Naw, I think what started all of the ruckus was when GM came out with the W bodies. Those cars had crap brakes to begin with and they almost refused to stop at all if the rotors were resurfaced. (yeah, and I am taking into account the frozen calipers in the rear) In fact, that was the first TSB issued on the subject, to my recollection. (approx. 1988) If my feeble minds remembers clearly it stated that either the rotors were to be left as is or replaced, machining was verboten. That's also when they stated that a .060" groove was acceptable.

Anyway, my experience with those W bodies has shown that if you did machine them, you would have to wait until the pads polished the surface back to a mirror finish before the car would revert back to it's 'almost able to stop' ability. It seems as though the pads are so hard they ride across the 'peaks' of the machined surface, thereby resulting in a loss of swept area. Kinda far-fetched, but the most easily plausible idea.

Once they pitched the snowball from the top of the hill it kept collecting supporters for whatever reason. Funny, I test drive a car to check for vibrations before raising it up and pulling the wheels. But when I place new rotors on I always machine them out of the box before installing them, in order to avoid wasting time... It seems that auto parts have gone to h-e-double hockey sticks since NAFTA came into play.
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  #14  
Old 09-02-2002, 09:20 PM
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Beav , I will add to what you so wisely said about the rolling snow ball as I know exactly what you are getting at.

Quite recently I had a sports car which I ran in fun type classic racing and when I purchased it ( not from new ) it exhibited judder in the front right brake when stopped in anger and slight pulsing could be felt through the pedal.

I examined the rotors carefully and checked them with a dial gauge for both run out and thickness but could find nothing even slightly out of whack. Therefore I replaced the wheel bearings thinking one could be lumpy under load even though nothing could be felt spinning the wheel.

Back on the circuit and no improvement but a very slight skim fixed the problem and I go along with your comments re what amounts to surface texture having very real effect in some instances. Glazed pads also come into this same area of problem and can be a product of lack of use in anger !
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  #15  
Old 09-02-2002, 09:36 PM
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I don't know if they still 'season' cast iron parts as they used to years ago, but I'm thinking the answer is 'no'. When rotors, drums, engine blocks and cylinder heads were cast, they were tossed in a pile outside the factory and allowed to 'season' for a year or so. This allowed the metal to stabilize and yielded a better machined product when completed. That's why so many engine builders prefer to work with used blocks, etc. - the castings are totally stable after having been hot and cold thousands of times. I suspect that now the piece is sent directly to the machining pile as soon as it cools down to a couple hundred degrees.
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