Hi all,
When replacing rear brake pads should the rotors always be re-surfaced, even if they seem relatively smooth?

Thanks

if they were resurfaced every time they would get replaced more often. you can clean up the surfaces with crocus cloth in a circular motion to get the glaze off successfully. resurfacing is used more for removing damage caused by metal to metal contact of worn out pads. BUT if you are more comfortable having the rotors "turned" by all means do so.

Hi all,
When replacing rear brake pads should the rotors always be re-surfaced, even if they seem relatively smooth?
IMO, YES.
Surface finish is not as important as having a rotor run true. Re-surfacing will true it up (remove warpage) AND give a fresh surface for the new pads to "bed".

Yes resurface them. As Bill said it will true the surface, but also it will remove any old brake pad material imbedded in the surface. If they are different materials it can cause a hot spot and cause the new pads to glaze.

The old "turn-the-rotor" debate....

You cant really argue with the statement that it is BETTER to turn them everytime...

But is it necessary... in the real world.... No....

But is it necessary... in the real world.... No....

To do the job CORRECTLY...YES, it is necessary! :rolleyes:
Anyone that would just hang pads doing a brake job is ......and if you know how to run a brake lathe, not much is generally needed to come off to true the rotor...in the real world.

When I was in the business...absolutely! I would never send a customer out without truing his rotors while doing a brake job .

For myself? I won't true my rotors unless I personally have noted a pulsation in my brake pedal. This is just a choice on my part not a recommendation. Its my car and I do it my way.

One other thing, I always tighten my lug nuts in a star pattern and I bring them up tight in several passes , just like you'd torque headbolts.

I can't begin to guess how many zillions of rotors have been warped out of the box by tightening the lugnuts in a circle pattern , especially using an air impact wrench. For those of you who don't know what I mean by a "star" pattern ; you tighten one lug nut and then always go to the lug nut FURTHEST away from the last lug nut tightened.


The last above only applies to disc brakes. Drum brakes don't need any pattern as they aren't affected by warpage if you tighten them in a circle pattern.

The old "turn-the-rotor" debate....

You cant really argue with the statement that it is BETTER to turn them everytime...

But is it necessary... in the real world.... No....
I have to disagree with that...In the "real world" it is part of the job...My .02 ..what do I know...

Find out the manufacturer's maximum tolerences. The thickness variation, which is what causes pulsation, has a very low tolerence difficult to measure. It is best measured by feel when braking.

Find out the manufacturer's recommendation on turning. Chances are they recommend only 'on car' machining, and only if runout, taper, or thickness variation is past maximum. They generally will allow grooves to a specified depth.

Otherwise they normally recommend resufacing by various methods of sanding to remove the glaze without introducing excessive runout or making the rotors thinner.

Unless you check the service manual, you cannot say it is better to have them turned except as an opinion. Manufactrurers continually revise their recommendations based on what works best, and bench lathe turning of discs has failed the test of time. It works ok on older vehicles with tapered roller bearings and high profile tires, as the problems introduced are seldom noticed, or can be covered up.


In the real world, unless you get them turned while still mounted to the car, you might end up with more runout than you started. They will be 'true' to the bench lathe. This is why most service manuals after 1985 will specify 'on-car' machining only.

Unless you document runout before and after machining, you do not know, and only assume. The 'scratch test' is unreliable on the bench lathe.

My 00 Chrysler 300M calls for rotor replacement at brake jobs and no machining. Guess they're just super thin factory?

If they look like this I would.
http://img473.imageshack.us/img473/5714/oldrotor7ia.th.jpg (http://img473.imageshack.us/my.php?image=oldrotor7ia.jpg)
And resurfaced
http://img256.imageshack.us/img256/3859/10006558rp.th.jpg (http://img256.imageshack.us/my.php?image=10006558rp.jpg)
http://www.imageshack.us/

My 00 Chrysler 300M calls for rotor replacement at brake jobs and no machining. Guess they're just super thin factory?
Nope...not thin. Some rotors are so hard turning is not recommended.
In other cases, it's not cost effective either. When I did the brakes on Momma's Miata a few years ago, it wasn't worth the effort to turn rotors. Brand new Rabestos rotors cost me $13 each corner!

ok im a full time mechanic and do 25 brake jobs a week

YES U ABSOLUTELY CUT THE ROTORS EVERYTIME, just "slapping on pads" is hacking it. At our shop we just charge 5$ a rotor for cutting. Rotors are not, NOT cut because of the surface appearance. You can have a big groove in the rotor it doesnt matter. rotors are cut for 2 reasons, warped, or tapered. I do about 3 jobs a week where the owner wants to save a couple bucks by not cutting rotors. They are always back the next day complaining.

The 300M, is that direct from a service manual or bulletin, or quoted from a service advisor?

Generally I find that the service manual will state all of the parameters which would require rotor replacement, but not actually say that they need replaced every time, though on many vehicles they may be past tolerences for every brake job.


Here is an example of a rotor which was not machined. I did my own version of resurfacing.
http://www.spkorb.org/panrot01.jpghttp://www.spkorb.org/panrot11.jpg

This is the type of resurfacing I've done to hundreds of cars without issue.

I did on average 25 brake jobs a week for ten+ years. The first two were spent machining rotors on a bench lathe. I quit using it when we got an on-car. Other technicians still used the bench lathe. I could hear the rotors being turned poorly. Sometimes I hear it at the parts stores.

The 300M, is that direct from a service manual or bulletin, or quoted from a service advisor?

.


Advisor read it from a bulletin then proceeded to tell me "'bout $700 for a 4 wheel brake job" I laughed enough that I teared up a bit and went home and did them myself. Just cleaned them up with sandpaper and did not buy new ones. True to this thread a few weeks later I had pulsation so I am off to buy new rotors and do em over. Thought I could get by - no go.

I certainly didnt intend to ruffle feathers with my post, only gave my opinion....
My "real world" statement wasnt meant as an insult.... allow me the opportunity to restate my response.....

EVERYTHING we do our cars has many levels at which the job can be accomplished.... We each decide on the level we strive to obtain based on the end goal we seek to accomplish and the amount of resources we are willing to invest (including time, money, etc...)

Example.... The BEST way to build an engine may be to hand select all components, then run exhaustive metallurgical testing on them, then balance them to scientific standards, then assemble them in a "clean room"...
No one could argue that this would produce a great motor... but is that NECESSARY based on your NEEDS vs. RESOURCES?? Most of us decide the level of performance we seek and build according to resources to meet that goal..... (that's what I meant by "real world")

The necessary operation of your brakes includes performance and reliability, both of these things are relative.... If you do not turn a perfectly appearing and operating rotor, that the pads were not allowed to wear out completely, would the brake system not perform or be unreliable? If yes, is that to any appreciable amount??

I would never tell anyone NOT to turn them (unless it was against mfg recomendations) but I doubt the average application would see any real measurable gain by turning rotors that showed no sign of problems.



The above is just an opinion...

I have seen very few "no rotor turning" brake jobs turn out well. I tried to get away with it on my wife's 1994 Honda Accord because it is a huge pain to get the rotors off the car (anyone else with that era Honda knows what I mean). My wife is the type of driver that could seriously put 100,000 miles on a set of front pads - hence my decision to just slap pads on. Whoops. Had to have it taken in about 5 days later because of the vibration from out-of-true rotors. That vibration never showed up with the old set of pads. I also saw this happen many times when I worked at an auto shop - people try to save $10 and end up having to pay for the labor to take the car apart twice. Always put the rotors on some sort of lathe!

Ryan

If it doesnt vibrate when you have old pads on, why would it vibrate and be out of true when you put new pads on without turning? I am about to do my own brakes on my honda. I have done brake jobs before, but they both needed new rotors, so no need to turn. I think my honda could go for another pad session before replacement, so it would be nice not to have to true them. It just doesnt make sense to me why new pads would cause vibration to show after only 5 days. I know someone will have my answer.

they dont have to show a vibration. theres a 80% chance they will squeek alot, and they will (this is 100%) they will wear out faster.

if someone insists on just putting disc-brake quiet on the back of the pads and hacking it like that, its your car go ahead. Its just another 5 bucks per rotor or so to have them cut.

OK, here is the real skinny on rotors. Rotors do not warp or change their shape as a result of brake use. Think about the temps that average brakes run at. Extreme HP pads are only good to 900* or so and nobody here is running pads like that but me and mine are coming off. So given that the average pad is only good to about 600* or so that means the average board member would believe that a chunk of iron has a malleability temp of less than 600* and results in "warpage". "Warpage" is really excessive pad deposits left imbedded in the rotor. Since the pad deposits are not left in a uniform fashion (think about when apply the brakes; after the stop is complete you still have the pad firmly pressed against the rotor in one place) over time these heavy deposits cause pad knock back while braking, commonly referred to a "brake pulsation".

The problem is that 90% of the mechanics out there do not fully understand the automobile and the principles with regard to how it operates. As a result we get lots of misinformation that to most makes some sense so it becomes accepted as fact. Even if the pad deposits are not heavy enough to cause a brake shudder they are still present and there is positively no way for the new brake pads to properly "bed" into the rotors without a clean/fresh surface. If the pads are not properly bedded in, braking capacity is reduced as it the danger of brake fade once heated to the point of pad composition breakdown.

.... so your saying when i use our brake lathe.......... and i measure that i had to cut a total of 15 1000ths to eliminate the warpage..... and that steel dust falls down to its catch container...... your trying to say that that 15 1000ths of steel dust is really brake pad material?

leading cause of warped and tapered rotors is bad caliper slides. Whether the caliper bolt functions as a slide or if the bolt is independent of the slide, its the main cause of damaged rotors. A good mechanic will take the slides out of a caliper and wire wheel everything, and then coat it all with grease.

I guess if its deposits, thats why we need to get the rotors turned, so the new pads will fit over the rotor, but wait, when I take my rotors in to be turned and they are too thin to turn, how can that be? with all those deposits they can't be getting thinner.:confused: They warp from heat, riding the brakes will do it too. We are not talking 1970 here, I think I read somewhere that there are 24 beer cans and 24 rolls of pennies in a new brake rotor :D and in fact, pull them outta the box at the parts store and I would bet 50% will show runout. They don't make em here anymore guys, our government, epa,lawyers, etc etc have run em off shore.

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml
http://www.performanceoiltechnology.com/brakingsystems.htm
http://www.babcox.com/editorial/bf/bf100326.htm

so your saying the runout on a "warped rotor" is 15 1000ths of brake pad fused to the rotor? it sure looks like steel when being cut on a lathe, and it sure does rust like steel too

Check the links guys (thanks chevry, I've never seen those. I especially like the one by Carroll Smith, the leader in racing diagnosis and analysis). I guess me AND every nationally recognized expert in the brake field are all wrong.

Please continue to believe the kid at Midas, he probably has much better understanding of braking system properties and pad binder properties.

I guess if its deposits, thats why we need to get the rotors turned, so the new pads will fit over the rotor, but wait, when I take my rotors in to be turned and they are too thin to turn, how can that be? with all those deposits they can't be getting thinner.:confused: They warp from heat, riding the brakes will do it too. We are not talking 1970 here, I think I read somewhere that there are 24 beer cans and 24 rolls of pennies in a new brake rotor :D and in fact, pull them outta the box at the parts store and I would bet 50% will show runout. They don't make em here anymore guys, our government, epa,lawyers, etc etc have run em off shore.Pads are made up of semi-metallic material; amongst many other things, when you apply two pieces of steel or iron and a composition steel in the case of brakes together they WILL wear each other. The type of pad determines how much of the rotors will wear. As the pad wears into the rotor it also wears off material. Rotor runout has nothing to do with brake pulsations and every rotor has some runout. If you are talking about measuring parallelism then that is typically pad material and the leading cause of brake pulsations.

so your saying the runout on a "warped rotor" is 15 1000ths of brake pad fused to the rotor? it sure looks like steel when being cut on a lathe, and it sure does rust like steel too
Yep, brake pads are made out of very small amounts of metal composition and binders, they will rust just like regular iron and look like metal dust when it is cut off.

just cause they are semi metallic does not mean they will mock the appearance and texture of the factory steel of the rotor perfectly.

I think this is true to an extent, but its common sense when u get something too hot it warps. So when a car comes in that had a bad brake hose or caliper and has been driving around with the brakes applied for a couple months, those brakes hit a good 1000* and are warped. like i said before, bad caliper slides can force one pad to always be rubbing the rotor, making a whole lot of heat

this is true to an extent, but you cant apply it to everythibg that is rotor damage


EDIT: after thinking about it as i did 3 brake jobs today, i found a couple flaws with that BS theory stated

1. does that mean it is impossible for a rotor to be deformed if organic pads are used? (i think now, our garage only uses organic pads and 3 years after a brake job our customers return with warped rotors)
2. If this was true, a rotor would never get thinner, when turned on a lathe only the added material would be taken off, but somehow they always manage to get thinner
3. why does the brake pad material stick to one end of a rotor and not the other? (causing the difference in thickness from top to bottom)

You are right Rick, Stoptech (the industry leader in performance braking) and Carroll Smith (see any automotive library, many of his books are there and any he didn’t write will have reference to him in them) are probably wrong because you in your vast experience analyzing braking components, effects of overheat, computer mapping of heat cycles with the very latest in technology, and the 30 years of racing and designing brake components for race cars has determined it not be true? I didn’t think so. I would recommend rather than using “I thought of this today” as a rebuttal to WELL documented evidence from those who make their living analyzing, designing and running FEA all day long on brakes, you come in with something concrete.

I think this is true to an extent, but its common sense when u get something too hot it warps. So when a car comes in that had a bad brake hose or caliper and has been driving around with the brakes applied for a couple months, those brakes hit a good 1000* and are warped. like i said before, bad caliper slides can force one pad to always be rubbing the rotor, making a whole lot of heat 1000* is nowhere near enough heat to make a chunk of steel malleable. NASCAR rotors run hot enough to turn them yellow, way hotter than your average commuter with a stuck piston or slide. They don’t warp; I wonder why?


EDIT: after thinking about it as i did 3 brake jobs today, i found a couple flaws with that BS theory stated the BS theory huh? Based on what evidence (your personal thoughts don’t count as you have no experience in the FEA of braking components)

1. does that mean it is impossible for a rotor to be deformed if organic pads are used? (i think now, our garage only uses organic pads and 3 years after a brake job our customers return with warped rotors) Because organic materials cannot bond with iron??? WTF kind of analysis is that. I guarantee at 600* the organic materials coming off the pads are more than capable of bonding to the rotor.

2. If this was true, a rotor would never get thinner, when turned on a lathe only the added material would be taken off, but somehow they always manage to get thinner Again with the WTF?? Organic materials cannot wear another component? Better check your thinking.
3. why does the brake pad material stick to one end of a rotor and not the other? (causing the difference in thickness from top to bottom) Because no brake caliper applies complete and even pressure across the entire pad surface.

Don't concentrate so much on the material transfer aspect. It's not really mentioned that much in the articles anyway. Read the articles and think about thickness variation, and what really causes it. There is a reason you see your customers back in 3 years with 'warped' rotors.
I would recommend your shop invest in an 'on car' lathe.

Common sense doesn't always apply. Ideas disguised as logic can often be used just to BS your way through something. I learned this realizing that ideas used where I worked and at many other brake shops do not hold true. I listened and tried to apply those ideas to fill in the gaps between what I learned in school, and what I saw in the real world. After a few years, I realized it wasn't working.
When you see a rotor turned blue from heat, and there have been zero rear brakes for years from a rusted shut valve,
but the front (blue) rotors are still straight and true as the day they were born, it makes you think.

So then we got an on car lathe which came with a runout gauge. I used it a lot, and then bought my own gauge, and did a lot of thinking, and worked on a lot of comebacks, my own and others. I actually ended up getting stuck with most of the cars back on their 3rd time. The ones with the on car lathe never seemed to come back. I had the lowest comeback percentage of ~34 employees in 6 shops.

Let's see if this sounds familiar.
Scenario:
New pads, turn rotors on bench.
Comeback:Noise
Oh gee, you need your rear brakes adjusted. lets put on some new shims too.
Comeback:Noise
You must need calipers. They seem to kind of stick.
Comeback: Pulsate/Noise
Oh, gee, you have excess runout (now that I bothered to check). It must be because you got the brakes hot and went through a puddle. I mean, it's been a year and a half. It couldn't possibly be anything I did.

So after a few years working there, a customer would come in with a problem... squeak or whatever. They had the brakes done once. My shop maybe, somewhere else maybe.

Let's say, .007 runout one side, .012 runout the other.
"why" they ask.
What am I supposed to say? You went through a puddle with the brakes hot? You need calipers? You need a clean and adjust of the rears? That's what my boss would have me say. CYA

I quit. It took a long time to quit, and I might have to go back, but I hope not. I still make mistakes, but I've tried to cut back. CYA.


http://www.urbandictionary.com/define.php?term=A+duck!

1000* is nowhere near enough heat to make a chunk of steel malleable. NASCAR rotors run hot enough to turn them yellow, way hotter than your average commuter with a stuck piston or slide. They don’t warp; I wonder why?
yes, 1000* is more then enough to make steel malleable. idk about your metal working experience. Im getting the impression all of your experience is reading articles online and you have never turned rotors or worked metal, but steel is mallable at 100 degrees. get a piece of steel, smack it with a hammer, it will begin to flatten. One smack of a hammer to a cold rotor will cause some runout, And the hydraulic force of that caliper is alot stronger then a whack of a hammer. and you said yourself that no calipers have even force...


Because organic materials cannot bond with iron??? WTF kind of analysis is that. I guarantee at 600* the organic materials coming off the pads are more than capable of bonding to the rotor..

ok, your saying organic material, will bond to steel, and have the exact same appearance as steel? no, they wont, someones defense on this issue was metallic pads have some steel and iron in them, making it possible. organics have no steel in them, therefore there is no steel to be bonded to the rotor. When you cut a rotor, the entire surface is a uniform color and texture, i think a chuck of organic material will be noticable

Again with the WTF?? Organic materials cannot wear another component? Better check your thinking. Because no brake caliper applies complete and even pressure across the entire pad surface.

NO, a SOFT organic pad will not wear away steel, organic pads are extremely soft, dont last very long, and do not wear down the thickness of a rotor.

bottom line, rotors warp, you can sit there and try to argue how, but they warp, if there is runout, its "warped", when you mount it on a lathe and it does not spin true, it is warped. rotors warp.

im sorry i just dont go and believe anything i read online. Theres alot of BS involving this industry thats just spoken of to sell parts. "Stoptech" is just trying to sell parts. The only reason they would do "research" and create "theories" is to profit from it. They are just trying to sell parts

EDIT: whoa whoa whoa, i just read your little article from stoptech, and when they are talking about pad material fusing to the rotor, they are talking about this http://www.stoptech.com/tech_info/img/warped_4.jpg

they arent talking about why a rotor that looks like this is warped http://hock.net/images/bmw/rear-brakes/rear-brakes-old.jpg

For what it's worth, GM's official position is not to turn them unless therre is a pulsation or vibration problem. To be honest with you I think it has a lot to do with the way you drive, and how badly you "punish" your brakes. I have been driving since 1966 and have owned quite a few cars and driven who knows how many miles, yet I have never had to turn a rotor or drum on one of my own vehicles. I just did the brakes on my 99 Tahoe about 3 monhs ago at 65k miles. Just put the new pads on when I heard the wear indicators and was done with it. No problems before, no problems now. My Wife's 84 Riviera is on its third set of pads in about 130K miles, have never turned the rotors or drums, still stops as nice as it did the day it was new.

The other thing is, I use GM OEM pads and shoes only. Not aftermarket, not GM Goodwrench (which is just aftermarket reboxed) The OEM pads come with all the hardware etc. You have to specify them.

I do turn a fair number of rotors and drums at the shop for customers, and most of them are out of round or warped a bit, so there is a need to do it in a lot of cases.

actually yea it happens, when a rotor is stuck to a hub, u have to smack the part inbetween the studs with a hammer to loosen it, and sometimes u miss

Yayy BillK!
Don't turn'm unless you have to.

edit:
For Rick's benefit, my deleted post asked if he was smacking rotors with a hammer. And, yes, your subsequent post holds truth.

yes, 1000* is more then enough to make steel malleable. idk about your metal working experience. Im getting the impression all of your experience is reading articles online and you have never turned rotors or worked metal, but steel is mallable at 100 degrees. get a piece of steel, smack it with a hammer, it will begin to flatten. One smack of a hammer to a cold rotor will cause some runout, And the hydraulic force of that caliper is alot stronger then a whack of a hammer. and you said yourself that no calipers have even force... Actually my experience is far greater than yours. I have trained exclusively in braking and suspension with both independents and Chrysler for 15 years. I also hold a cert in welding technology so I have a fair amount of knowledge working with metals and heat. My current position involves welding on a daily basis with all types and configurations of materials. Smacking a rotor with a hammer is a far different type of metallurgy than you are talking about. Yes calipers have far more force to exert on the rotor but it is done in nearly the same fashion.

ok, your saying organic material, will bond to steel, and have the exact same appearance as steel? no, they wont, someones defense on this issue was metallic pads have some steel and iron in them, making it possible. organics have no steel in them, therefore there is no steel to be bonded to the rotor. When you cut a rotor, the entire surface is a uniform color and texture, i think a chuck of organic material will be noticable Organic pad material imbedded into the rotor over several thousand heat cycles and millions of revolutions will leave the illusion of darkened iron. When rotors are machined (yes I have a turned a rotor or two, or thousand) the .005” of material being removed would very difficult to distinguish as either iron or some other compound.
NO, a SOFT organic pad will not wear away steel, organic pads are extremely soft, dont last very long, and do not wear down the thickness of a rotor. Yes, organic pads will wear rotors. I don’t care what they are made out of, if you apply a substance to a chunk of spinning iron in an attempt to stop it there will be some wear. The amount of wear is dependant upon the type of material being used, the quality of the iron in question, and the amount of force being applied over what distance.
bottom line, rotors warp, you can sit there and try to argue how, but they warp, if there is runout, its "warped", when you mount it on a lathe and it does not spin true, it is warped. rotors warp. Is it warped or is there a thickness variation from some other source? im sorry i just dont go and believe anything i read online. Theres alot of BS involving this industry thats just spoken of to sell parts. "Stoptech" is just trying to sell parts. The only reason they would do "research" and create "theories" is to profit from it. They are just trying to sell parts Yeah, that’s it. How do you explain Mr. Smith coming to the same conclusion? If you like I can provide the sources from another dozens experts with the same conclusion, none of which sell brake parts. How does Stoptech explaining the myth behind warped rotors help them sell parts? EDIT: whoa whoa whoa, i just read your little article from stoptech, and when they are talking about pad material fusing to the rotor, they are talking about this http://www.stoptech.com/tech_info/img/warped_4.jpg

they arent talking about why a rotor that looks like this is warped http://hock.net/images/bmw/rear-brakes/rear-brakes-old.jpgSame thing, just a more exaggerated viewpoint.

Doing up lug nuts with an impact gun doesn't help things either. I don't know anyone whose judgement is as good as a torque wrench. I don't think that the replacement rotors today have any quality materials either. I have an '87 S10 truck with its original rotors and they work fine through salt and what ever else that gets thrown at them. The rotors on our Saturn, however, got replaced every two years with the metal litterally rotting off the rotor faces. Even if they weren't rotting apart there would be virtually no material to machine anyway without going undersize. I've never had a rotor problem with our '69 Chevelles. Our original car never had a brake job in its lifetime on the road. With 11-1 compression, 4 speed and 4.10 gears, you don't have to use the brakes much. Downshifting did most of it. Our SS396 car has the two piece rotors and I assume that they are the originals. They work fine too. Something has gone south over the years and I don't think that the pads are entirely to blame. Any thoughts?

i cut 4 rotors at work today, none had those little black spots of pad deposits. All had a uniform grey color across the entire surface.

but somehow i had to cut 13 1000ths off each side to get rid of a warp. Only half the rotors surface area would touch the cutting bit. It wasnt small blotches of black spots like stoptech showed, the entire width of the surface was warped, equally on both sides

"The old "turn-the-rotor" debate....
You cant really argue with the statement that it is BETTER to turn them everytime...
But is it necessary... in the real world.... No...."

I REJECT your reality and substitute my own: Resurface them every time. Do the job right.

As long as the runout After resurfacing is checked with a runout gauge On the car, and is within spec, I would have to agree.

Unfortunately you may not have a good chance of this happening. Even the best tech can get fed up trying to get an uncooperative rotor to turn straight... and if he can't measure runout before and after... well, I made my point about that before I think.

A reconditioned rotor with no runout is better than a resurfaced rotor with excess runout (edit, assuming no brake shake). Runout will not cause brake shake... for quite a while.

In my garage rotors get 1)reconditioned (looks like turned), 2)replaced, or 3)referred to a shop with an on-car lathe (until I own one), depending on the situation. I WILL NOT have any of my customer's rotors turned on a bench lathe. If I had to, it would be at a machine shop, not a brake shop or parts store.

EDIT:
Unless there is a hub problem, or the rotor was once turned on a bench lathe, you shouldn't have to take much more than .005" off a "warped" rotor when using an on-car lathe. Tapered/grooved rotors are the exception.

IMO, YES.
Surface finish is not as important as having a rotor run true. Re-surfacing will true it up (remove warpage) AND give a fresh surface for the new pads to "bed".

Correct. I would resurface them "lightly." Try to take as little off as possible just so you can get them true. If this is your second time replacing the pads, I woud say to buy a new set of rotors. In any event, cars that take heavy braking abuse will need new rotors every time they go through a new set of pads. If you cut too much your first time, or are cutting a second or third time, they will be two thin, and they will warp that much easier.

Dan

ok i spoke with the "90% of mechanics that dont know anything" today, and brought up this discussion we've been having.

heres what i was told, i'll just try to quote it the best i can...

"of course they warp, but how malleable the iron of a rotor is has nothing to do with it. If a rotor was made of 100% pure iron, then yes it would probably never warp. But something like a rotor is typically 90% pure, meaning that 10% is random imperfections in the metal. Rotors warp because of heating and cooling cycles, and the impurities (forgive me if i spelled that wrong) heat and cool at a different rate then the iron ones do. This causes the warping of a rotor."

I used to work with them. I know those guys ;)
They sell parts.

The main cause is constant uneven contact of the pad to a rotor with excess runout wearing the disc down in spots, or causing uneven pad deposits, while driving (not while braking) causing a thickness variation.

Thickness variation causes pedal pulsations.

What about an obviously cheap rotor with random rust pitting but no pulsation. It's cheap metal. It's been on for a while with heat/cool cycles, but it's not warped. Why? .002" runout.

How about one with a bad hose or caliper, obviously overheated many times but no pulsation? I guess they never drove thru a puddle in the last 6 months while the problem was becoming more serious. Or they just never let it cool down? .0015" runout.

How about one which looks like it never even got very hot but has .007" runout? Where did the runout come from?

http://weisstool.com/store/products/CEN-6450.jpg
Your shop should have one.
Use it before and after EVERY brake job.
Shoot for >.003"

My above post oversimplified and just gave 3 examples. Runout does not in itself cause pulsation, and heat/cool cycles don't either.
Your post mentioning stuck slides was intuitive.
You have the potential to become excellent.

Bowing out, impossible to win an argument when the opposing side brings zero tech to the table but continues with the he said/she said/my buddies said theory.

For those following, the evidence has been presented, please read it and deiced for yourselves. Basing your own opinions on the words of those who repeat information as it has been learned from the folk tales and argues with well documented and respected test data from every major brake company, brake expert, chassis developer, race car engineer, team owner, etc.. is a little foolish.

My previous links back me up.
Pad deposits you mentioned are part of it, sometimes for the same reasons... usually with unconditioned discs IME. Like I said, I oversimplified.
I edited the other post to help there. DTV caused by thickening or thinning I have not the technology to detect.
The stoptech article blames pad deposits. Fine (they look like hot spots).
The 2nd article, published in Brake&Front end magazine, only mentions that DTV happens. I read it when it came out. Thick or thin spots it's DTV.
The 3rd article supports thin spots. This was relayed to me about 1994 by a factory O-C lathe rep, so I'm biased towards it, but the deposit theory still holds merit with me.

I am also a Technician and have been for over 10 years. I have done my fair share of brake jobs and I can tell you that rotors arent just going to warp without some sort of abuse of the brakes like mentioned several times already.

I will also mention that 90% of the rotors I have seen causing pulsations are because of badly rust pitted surfaces. This is especially true on Chrysler products like thier line of mini vans although that last few model years have seemed to have been improved.

i've seen rotors have .020 needed to be cut out to get rid of warping.

ok, personally i dont care what you say, i work on cars for a living til i get my masters in engineering, i have the experience of 10 years with brake jobs, and cutting all those rotors taught me alot. And doing brake jobs w/o cutting rotors has also taught me alot

but go ahead get on your high horse because some guy on some website said some stuff so your gonna praise it. I had a calculus professor who would call you a cheerleader

The magazine article came out in 2000 in Brake&Frontend Magazine, written to assist people in shops.
At the time, the entire article backed me up with what I had been trying to convince my co-workers for some years. They didn't listen then, they didn't like the article, and apparently they wont listen now.

I didn't form my ideas around these articles. I found the articles to back me up. They just happen to be from reputable sources. I have about ~20,000 brake jobs and inspections under my belt.
One of many reasons I quit was I was tired of working on other's pulsation comebacks.

star patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar pattern...ok...I feel better now :)

star patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar patternstar pattern...ok...I feel better now :)

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