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Old 01-25-2007, 01:02 AM   #21
Alex323Ci
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Quote:
Originally Posted by Rob Levinson
I just have to comment on a few funny things in this thread:

"I read somewhere that the oe rotors are balanced for our BMW's and that is why we should purchase them from BMW."

Why would anyone think that balancing is done differently for a BMW? Do other brand cars' wheels turn slower? Balanced is balanced, and all good name-brand rotors are balanced.

"bmw puts the specs so that one can resurface the rotors."

No, BMW puts the min thickness specs on the rotors so you know when they're worn out. They don't put an expiration date on milk cartons so you can refresh it with a time machine.

Rotors are consummable items and get used up. Just like the shocks/struts, clutch, tires, chassis bushings, oil, ignition coils, water pump, alternator, etc., many of the parts of your car are designed for periodic replacement. None of them are worth repairing, just throw 'em in the recycle bin and install a new part.

Arguments against turning BMW rotors are very simple:

1) Minimum thickness is not much less than brand-new thickness. A used rotor, already worn down, loses more material when turned. What have you gained? A solid two months' worth of usable rotor life?

2) For the cost of labor to remove, turn, and re-mount... all just to have used rotors put on the car... you've just spent a big chunk of the cost of new rotors. Simple math: 1/2 hour of labor @ $55, plus $35 for turning, $90 spent. Compare to $100 for economy blank rotors, or $175 for premium slotted/plated rotors.

3) A turned rotor no longer has the same finish as a new blanchard-ground disk (or a normally worn disk with a smooth finish created by pad wear), and with today's sensitive high-tech pad materials and sensitive drivers, an objectionable noise or vibration is possible.

While being a Master Tech or having lots of experience makes the concept quite clear, this logic should be obvious to any layperson.

- Rob
Only one of these points you made address or gives a reason why one CAN NOT turn rotors. That is the point about the rotor not being blanchard-ground surface to the pads. Then again some might use a different pad material than the OEM graphite based pad and that doesn't seem to be as important a point then. But very valid none the less. If someone gets their rotors turned for free then where does that leave those other two points dealing with only cost as their issue?? On the other hand, one only needs one good reason. Safety.
Back to the point you made about the minimun thickness stamp on the rotors. The Bentley Manual in BRAKES 340-9 states under the heading of Brake Rotor Reconditioning Specifications the Max. machine limit per friction side..and the chart. This refers to machining the rotors or turning them. I agree that rotors are parts that wear out and are thrown out. But it appears obvious to any layperson that brake rotors have been reconditioned/resurfaced when within spec and the Bentley Manual technicians/writers agree. Me, I don't own a parts company or a service garage, I'm just a simple layperson
-Alex
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Old 01-25-2007, 02:28 AM   #22
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Serious question for you... are you simply discussing this at the hypothetical level, or are you really suggesting that turning the rotors makes sense? I'm all for discussing the hypothetical, but somewhat less warm for beating my head against a wall.

Quote:
Originally Posted by Alex323Ci View Post
Only one of these points you made address or gives a reason why one CAN NOT turn rotors.
Well, that's accurate. You could have your OE shocks rebuilt, you could have your tires retreaded, and you could re-purify engine oil... none of which makes any sense for all similar reasons, that you end up with a used part of limited remaining lifespan at similar or greater expense than buying replacements.

Quote:
If someone gets their rotors turned for free then where does that leave those other two points dealing with only cost as their issue??
Just as likely, what if someone gets new rotors for free?

What if leprechauns installed them while unicorns watched?

Quote:
On the other hand, one only needs one good reason. Safety.
Back to the point you made about the minimun thickness stamp on the rotors. The Bentley Manual in BRAKES 340-9 states under the heading of Brake Rotor Reconditioning Specifications the Max. machine limit per friction side..and the chart. This refers to machining the rotors or turning them.
Bentley does a cut-and-paste of the same brakes chapter they've had since disk brakes appeared in the '50s. Bentley also has a DIY on an engine rebuild, which also is not feasible (data: engine rebuild at $8K versus good used engine at $3K).

You are also missing one other critical safety point. What's the reason that rotors might need to be turned? Odd vibration or shimmy, right? Meaning that there's something wrong with the rotor.

While one cause of brake vibration can be melted pad deposit, in which case a "surface true" will remedy the problem, the fact remains that traditional rotor turning is done in cases of rotor damage... back when rotors were made thick enough to be worthwhile to turn, and a pad was run down to the backing plate and scored the surface, you could turn the rotor to fix it. However, with the miniscule wear depth limitations of modern rotors, a pad scoring is likely past the wear limit.

Look at the hard numbers; the basic E46 rotor is 22mm thick when new. Minimum thickness spec is 20.4mm That means there is an allowable 1.6mm total wear, which means only .8mm per side. Less than 1mm is a very small amount!

The reality is that a set of rotors may barely out-live a set of standard pads in normal use. How much material do you think a truing will remove?

Secondarily, if there is something actually wrong with the rotor such as a defect warp, over-torqued lug bolt warp, or even the rare heat warp, then turning will simply not fix the problem because a warp for any of the reasons above is exaggerated with heat, when the brakes are being applied.

Quote:
I agree that rotors are parts that wear out and are thrown out. But it appears obvious to any layperson that brake rotors have been reconditioned/resurfaced when within spec and the Bentley Manual technicians/writers agree.
First, the point remains that the window of opportunity for resurfacing a BMW rotor is very small, bare fractions of a millimeter seperate a new-spec rotor from worn-out.

Secondly, the Bentley writers aren't "agreeing" with anything. They are describing something that you could do, but not something that makes sense to do.

Quote:
Me, I don't own a parts company or a service garage, I'm just a simple layperson
-Alex
And you know what the difference is? None whatsoever. The same cost differences and common sense conclusions exist for the layperson and those "in the business".

But hey, if you want to turn your rotors, then that's something you should do.

- Rob

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Old 01-25-2007, 03:17 AM   #23
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what can us 323 guys do for brake upgrades? Can I run 330 rotors? what needs to be done to fit?
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Old 01-25-2007, 04:56 AM   #24
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Originally Posted by jeguana View Post
what can us 323 guys do for brake upgrades? Can I run 330 rotors? what needs to be done to fit?
Since the 323/325/328 all use the same calipers, to do a small upgrade, you can simply change our your 323 carriers for either a 325 or 328 (those two cars use the same rotor size). Do a search to see a thread where I posted part numbers. You'll be able to put on slightly larger rotors with this upgrade.

If you want to put on 330 brakes, you're gonna have to do a couple of things. First and foremost, you'll need at least 17" rims to clear the calipers. You'll need the whole brake assembly from a 330 which includes calipers, carriers, and rotors.

I couldn't find any 325/328 carriers in time to upgrade my 323 brakes this time around. I found a set of four from a 325 from a junkyard, but when I called, they wanted $300 for them. I tried to get them to lower it and the guy went down to $250+shipping. I didn't bite cuz I thought that was a little high for used parts that you could get for around that price new at the dealership.

If you end up doing this, please let me know if you find a good source for 325/328 carriers!
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Old 01-25-2007, 05:48 AM   #25
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Originally Posted by Rob Levinson * UUC Motorwerks View Post
Serious question for you... are you simply discussing this at the hypothetical level, or are you really suggesting that turning the rotors makes sense? I'm all for discussing the hypothetical, but somewhat less warm for beating my head against a wall.
Actually let's be honest..you're more sarcastic-condensending than simply discussing. But that is your flair. Just as long as we both agree beforehand what myself and other forum members are up against. I'm in for the wrath of God..I mean Rob..I mean God

Quote:
Well, that's accurate. You could have your OE shocks rebuilt, you could have your tires retreaded, and you could re-purify engine oil... none of which makes any sense for all similar reasons, that you end up with a used part of limited remaining lifespan at similar or greater expense than buying replacements.
Also one doesn't throw away the wheel when replacing tires. Nor does one replace the windshield when replacing the windshield wipers. But many do often keep the strut mounts and/or springs when installing new shocks. And one doesn't throw away the rear brake rotors if the parking brake pads are worn. And we do fix a flat and not throw away a new tire. The first two extreme examples like you've shown. Let's meet somewhere in the middle as we both know rotors are still reconditioned in this day and age. It's not like they never were, even on vented rotors.

Quote:
Just as likely, what if someone gets new rotors for free?
What if leprechauns installed them while unicorns watched?
People have many connections in this wide world of ours. Mine may not be access to BBK and free rotors, but resurfacing has been one of them. Sorry no leprechauns or unicorns in the world I live in. Back to the point I had made that you made light of... Your points have only credit when discussing and comparing to monetary value. When that monetary value is taken out of the equation then it's a moot point. My only discussion is why they "Should Not Be Turned"???.

Quote:
Bentley does a cut-and-paste of the same brakes chapter they've had since disk brakes appeared in the '50s. Bentley also has a DIY on an engine rebuild, which also is not feasible (data: engine rebuild at $8K versus good used engine at $3K).
The Bentley used to show how to bleed the brakes, but has upgraded to telling the readers of this model car to do only with the adequate machine/tools. If your defense is that turning the rotors is just not feasible, then that's fine. (You don't need to try and find other non feasible material in the Bentley Manual. It's a specialized "information" manual, that's all it is). But that still in no way makes turning the rotors damaging. Does it?

Quote:
You are also missing one other critical safety point. What's the reason that rotors might need to be turned? Odd vibration or shimmy, right? Meaning that there's something wrong with the rotor.
I feel that turning the rotors makes the surface readily available for the pads to be bed in. Also so as to not cause irregular wearing and then cause problems. It's more preventive so that things don't become a problem.

Quote:
While one cause of brake vibration can be melted pad deposit, in which case a "surface true" will remedy the problem, the fact remains that traditional rotor turning is done in cases of rotor damage... back when rotors were made thick enough to be worthwhile to turn, and a pad was run down to the backing plate and scored the surface, you could turn the rotor to fix it. However, with the miniscule wear depth limitations of modern rotors, a pad scoring is likely past the wear limit.

Look at the hard numbers; the basic E46 rotor is 22mm thick when new. Minimum thickness spec is 20.4mm That means there is an allowable 1.6mm total wear, which means only .8mm per side. Less than 1mm is a very small amount.
the reality is that a set of rotors may barely out-live a set of standard pads in normal use. How much material do you think a truing will remove?
Secondarily, if there is something actually wrong with the rotor such as a defect warp, over-torqued lug bolt warp, or even the rare heat warp, then turning will simply not fix the problem because a warp for any of the reasons above is exaggerated with heat, when the brakes are being applied.
First, the point remains that the window of opportunity for resurfacing a BMW rotor is very small, bare fractions of a millimeter seperate a new-spec rotor from worn-out.
Extremely good points. Not much disagreement there.
Quote:
Secondly, the Bentley writers aren't "agreeing" with anything. They are describing something that you could do, but not something that makes sense to do.
I think the Bentley writers are showing something that has been done and can still be done. Not something that Should Never be done. This fact was only brought up as you stated funny things brought up in this thread. You then proceeded to list the quote of 'bmw puts the specs so that the rotors can resurface the rotors' as one of the funny things and you Rob replied "No, BMW puts the min thickness specs on the rotors so you know when they're worn out". I dunno, it seems like the two are related. Minimum amount that a rotor can be machined/recondition before it's "worn out". Wouldn't you agree now?

Quote:
And you know what the difference is? None whatsoever. The same cost differences and common sense conclusions exist for the layperson and those "in the business".
But hey, if you want to turn your rotors, then that's something you should do.
- Rob
Now had you just said that, we could have agreed long ago. It's something that CAN be done, May be done, but maybe not the most cost effective thing to do. But are you saying it's something that "Should Not Be Done?" If so then simply what is this safety reason??? That is all I'm looking for. Tell me the rotors explode, the pads shread, the lathe causes molelular changes that burn the metal and they can never bed-in correct again. Anything truthful why they Should Never be Turned, as I don't want to have injury or cause injury. But if it's just injury to one's wallet. That's not the answer I'm looking for and is not what was being discussed earlier.
Thank you for your invaluable time. Now be nice in your rebutal or I'll take off my trick UUC stuff and get Rogue stuff instead. But I'm still keeping the UUC hat(that MaxHat brand is the best hat I've ever come across).
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Old 01-25-2007, 08:25 AM   #26
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Not quite, but there's definitely a trend toward replacement.

Here's why...

Our brake lathe went in the trash," a Mercedes-Benz service manager tells Master Technician. A veteran brake trainer says, "Within the next five years, you won't see a brake lathe in a shop." A successful Euro car specialist tells us, "We've gotten rid of our brake lathe. The tolerances on late models are so close, any appreciable wear demands that the rotors be replaced."
Yup, fewer and fewer professionals in the auto service business are machining discs. They've sworn it off in favor of buying new ones. Now that's a profound change considering that it wasn't very long ago when every shop in the galaxy automatically turned rotors during a reline providing they weren't already down to their legal throw-away thickness. That process was supposed to give a nice, fresh face that would break in along with the pads. Well, as Greg McConiga, former NAPA/ASE Tech of the Year and honored colleague at MT, puts it, "We need to take a stand on the old 'turn 'em every time' baloney and tell them that if there's no runout or DTV (Disc Thickness Variation), and if they're thick enough, you can't beat a work-polished rotor surface."



Early Glimpse

We were tipped off to this trend way back in '97 by a Pontiac TSB. During normal pad replacement, it said, use the discs as-is providing the grooves aren't deeper than .060 in. If those concentric furrows exceed that limit, replacement is the remedy. And in high-pedal-effort situations, GM wanted you to buy new rotors if the originals have ever been turned. In essence, the biggest carmaker in the world was telling us brake lathes are obsolete.


It's not likely that you'll be machining futuristic discs like this fiber-reinforced ceramic composite SLR McLaren specimen (courtesy Mercedes-Benz).

Obsolete? Providing you do what's necessary to achieve a fine finish, not necessarily.

Blasphemy and revolution! But there were two good reasons why this bulletin came down from on high. One, rotors have gotten pretty skinny, and the thinner they get the less able they are to absorb and dissipate all that heat, and to withstand warpage. As one brake company tech trainer tells us, "I agree with the GM recommendation that if the rotors aren't in bad shape and there's no complaint, why refinish them? There isn't a whole lot of extra meat to take off today." While the notion of "hanging pads" might be offensive to your sense of craftsmanship, just get over it.

Two, noise and hard pedal complaints and prematurely worn-out linings are very common with some of the brakes out there (the big company was having lots of trouble with friction formulas in those days). The factory service engineers believe these problems are promoted and compounded by poor machining procedures that leave a rough or inaccurate surface. Also, it's been proved that discs should be as smooth as possible in order to produce maximum stopping power, and sloppy turning will actually make a rotor rougher than it was when it came off the car.
So that leaves replacement,That doesn't mean, however, that there are never cases where machining is appropriate, as we'll explain.



Wobbly

But installing new discs isn't necessarily a guarantee that you won't get a repeat pulsation complaint. As Wally Marciniak, Manager of Technical Services for Affinia Under-Vehicle Group (Raybestos brand, www.raybestos.com), puts it, "A lot of people assume that just putting new rotors on will eliminate the problem. But you need to clock them in to get the least possible runout. Check and record runout in all of the possible mounting positions, and use the one with the least. The true runout of any rotor is when it's tightened down on the hub." Most authorities say you shouldn't have over .002 in. of wobble, while others say .001 is the limit.




As we hope you're aware by now, you can keep from causing runout problems by always tightening lugs with a torque wrench instead of your thermonuclear impact gun. Use the proper pattern, please.



A neat way of reducing runout to just about nil is to use tapered shims, such as those made by Brake Align (www.brakealign.com), between the disc and the hub. Of course, you already know that you've got to get those hubs as clean as possible so you don't get a mounting error.



Chain of Events

You may be asking, "Floating and sliding calipers should just ride with runout, so what's the big deal about some wobble?"


Sure, most calipers slide or float, so you might think they'd just ride with runout. Unfortunately, in the process the discs develop DTV.

Aha, there's a trick to it, something that many people don't understand: When it comes right down to basics, the direct cause of pulsation is DTV, which can also be seen as a lack of parallelism between the two sides of a rotor. The wobble we've been talking about causes the disc to wear unevenly as it hits those abrasive pads in one spot on each side every revolution. In other words, the contact areas will end up thinner than the rest of the rotor. One on-car lathe manufacturer claims that, typically, .002 in. of runout with zero-clearance bearings will cause about .0004 in. of DTV in 3,000 to 5,000 miles. Some authorities want thickness variation to be held to .0002 in., while others say it will take twice that to generate a complaint. Regardless, you can see that allowing any appreciable wobble out the door can be dangerous to your reputation.
There's yet another factor that aggravates the development of DTV on late models. To reduce rolling drag, in many vehicles the engineers opted for pre-loaded, zero-clearance front wheel bearings, which require a less scuff-producing toe-in setting. But with no end play to absorb hub and rotor imperfections, any runout at all causes contact between the pads and rotor, increasing the wear that results in thickness variation.



Hand #2

But there's always the other hand, isn't there? As you may have noticed, two of the absolutists quoted in the introduction specialize in European cars. At the shop where we were recently working, we'd sometimes pull the wheels off an upscale Euro and know that those discs needed to be replaced by just looking at them. We're not talking grooves. We mean a visible wide depression made by pad contact.
This is what we call the "Autobahn brake phenomenon." As Mohammad Vakili, Manager
of Technical Affairs for Continental Teves-ATE (www.conti-online.com), explained to MT, "Vehicle sensitivity in Europe is different ... linings are aggressive and tend to produce noise, which is dampened by a soft rotor. In Europe, they design them to wear each other proportionally. They use softer metallurgy than in the U.S. or Japan, where they have milder pads and harder rotors." So, where we Americans have become accustomed to thinking that rotors should last forever, in European vehicles they're supposed to wear out along with the pads. That's the price you pay for being able to "stop on a dime and get nine cents change," as a brake expert once said to us.
Most of us aren't Euro specialists, however, so we typically get reline jobs where the rotors are still plenty thick. As we said above, if your test drive reveals no pulsation, swallow your prejudices and hang those pads. In cases where pulsation was the reason the customer appeared at your door, you are probably doing the right thing by machining away the DTV. That is, as long as you take the time to maintain your lathe and use it properly. That's fodder for another article.


Nobody's going to argue with the stopping power of a BMW brake, but it comes at the cost of faster rotor wear than most of us are used to.



Looks About the Same, But . . .

When replacement is the proper path, how do you choose among the rotors on the market? Do you try to save the customer a few dollars, or would you rather feel confident that the job won't come back to haunt you?
Vakili tells us that since ATE already makes O.E. rotors, it doesn't fool around with manufacturing a cheaper version for the aftermarket. If you buy that brand, you simply get original quality. Marciniak of Affinia says, "Whenever a new car comes out, we buy an O.E. rotor and dissect it so we know we're producing original quality designs and metallurgy."


The configuration of those fins is an engineered feature. Quality replacements match O.E. no matter how complex, whereas off-brands just do what's easiest (courtesy Raybestos).

This O.E.-quality replacement rotor has a designed-in groove that improves pad wear and performance, and serves as a visual indicator (courtesy Continental Teves-ATE).

Besides metallurgy and internal structure, there's a factor that might cause serious problems with off-brand rotors that most people aren't aware of: hub chamfer. If the angle doesn't match the hub exactly, the disc won't seat right, leading to big trouble with runout and heat dissipation, yet some cheap items just use, say, 45% as a one-size-fits-all manufacturing convenience. Our advice: Buy brand name only if you want to protect your relationship with your customers and your schedule.



In a Nutshell


An on-car lathe is still an excellent way to assure hat a pulsation problem is well and truly solved (courtesy Hunter Engineering, www.hunter.com)

Here's the on-car lathe Subaru requires its dealers to have. Once you learn the set-up, it produces a beautiful finish (www.procutinternational.com).

In keeping with Master Technician's mission of offering immediately useful solutions, we'll boil the above down into a few rules:

If there's no pulsation and the rotors are still thick enough (look it up), just hang pads. You may, however, want to service non-unitized wheel bearings, in which case you should mark the rotor and hub so you can assemble them in the same relative positions.
Whenever you install discs, new or otherwise, get that hub perfectly clean and make sure you mount them in the position that gives the least runout. Also, tapered shims are a great way to eliminate wobble.


If the grooves are deeper than .060 in., you're justified in buying new rotors. An easy way to measure the depth of a rotor groove is to use a dime. If the top of F.D.R.'s head is still showing, you're within the .060 in. limit. If the groove's too narrow for the coin to be inserted, don't worry about it.


If there's a pulsation complaint, you have a decision to make: machine or replace. If there's still plenty of thickness left, you can machine off-car and hope for the best (we're assuming you know how to produce a properly smooth surface - contrary to popular belief, a mirror-like finish would be ideal). Or, you can increase your chances of success by using a good on-car lathe (make index marks for future reference). Finally, there are good reasons to opt for new high-quality discs: They'll be less apt to warp because they'll be thicker, you won't be spending time with the lathe, Of course, if the bumpy braking condition is due to a crack, the decision is made for you.


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Old 01-25-2007, 08:26 AM   #27
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Quote:
Originally Posted by Rob Levinson * UUC Motorwerks View Post

Just as likely, what if someone gets new rotors for free?

What if leprechauns installed them while unicorns watched?
- Rob
I need to put that in my signature lol!

Your other argument about not replacing the windshield when the wipers go or not throwing away the wheels when the tires go is a completely different thing.

The windshield is not consumable, neither are the rims (unless someone breaks or steals them) rotors are consumable and are meant to be eventually replaced.
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Old 01-25-2007, 08:27 AM   #28
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M models Must not be machined why do you think on the Hi perfromance car BMW sates this, is it possibale they know that turning rotors is a bad idea??




Front


Wear warning from residual lining thickness 3.0 mm

Brake disc minimum thickness,(MINTH) is stamped in brake shell ventilated 20.4 mm

Brake disc minimum thickness,(MINTH) is stamped in brake shell 330 all ventilated 23.4 mm

Brake disc minimum thickness,(MINTH) is stamped in brake shell M3 ventilated 26.4 mm

Max. machining limit per friction ring side M models must not be machined 0.8 mm

Different thickness on brake linings 0.01 mm
Radial runout of brake lining (measured at largest of brake lining)

Disc installed 0.2 mm

Disc Removed 0.04 mm

Surface finish of braking surface (fine ground) 0.5..3.5 Ra u

Brake disc diameter 323i 286 mm

Brake disc diameter 300 mm

Brake disc diameter M3, 330 all 325 mm

Rear
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Old 01-25-2007, 08:59 AM   #29
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Originally Posted by Mikaly View Post
Since the 323/325/328 all use the same calipers, to do a small upgrade, you can simply change our your 323 carriers for either a 325 or 328 (those two cars use the same rotor size). Do a search to see a thread where I posted part numbers. You'll be able to put on slightly larger rotors with this upgrade.
There are very good rasons not to do that. By changing to another model's larger front brakes, you are affecting the brake bias. This can result in undesireable handling changes and even less effective braking due to premature engagement of the ABS in response to the bias change.

You should only change to larger OE front brakes if you are also upgrading the 325/328 rears.

And, unfortunately for all 328/325/323 models, conversion to four-wheel 330 brakes presents a problem also... the parking brake will not work. All the parts are a direct swap and it works okay, as long as you don't mind not having a parking brake.

With a 323, your best "economy" option is simply better pads, fresh rotors, stainless steel braided lines, and fresh fluid. Look to somehting like a low-dust Hawk Performance Ceramic "enthusiast" pad, or the semi-competition Hawk HP-Plus.

- Rob
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Old 01-25-2007, 09:08 AM   #30
Coldintake
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Originally Posted by Rob Levinson * UUC Motorwerks View Post
Just as likely, what if someone gets new rotors for free?

What if leprechauns installed them while unicorns watched?
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Old 01-25-2007, 09:25 AM   #31
Rob Levinson * UUC Motorwerks
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Originally Posted by Alex323Ci View Post
Actually let's be honest..you're more sarcastic-condensending than simply discussing.
HUH? I was never condescending. An assumption of that is absurd, when the desire to discuss and share knowledge is all that I offered. Ignorance or lack of experience is not an insult nore a sin, as long as one is willing to learn and consider basic facts and logic.

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But that is your flair.
But I'm wearing 15 pieces of flair today. How many pieces of flair do you want me to wear?

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Just as long as we both agree beforehand what myself and other forum members are up against.
What are you referring to? If it's a monetary constraint, I think I already demonstrated why turning rotors is "false economy" and costs nearly as much as basic new rotors.

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I'm in for the wrath of God..I mean Rob..I mean God
I'm not sure whether to be complimented or insulted! :lol All in good fun, right?


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Also one doesn't throw away the wheel when replacing tires. Nor does one replace the windshield when replacing the windshield wipers.
That's an argument ad absurdum.


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Let's meet somewhere in the middle as we both know rotors are still reconditioned in this day and age.
They're really not, and as was posted above, many dealer tech bulletins advise against it.


[QUOTE]When that monetary value is taken out of the equation then it's a moot point. My only discussion is why they "Should Not Be Turned"???.

How about they often cannot be turned? How much material a resurfacing removes varies, but less than 1mm is beneath the smallest amount many of the lathes can accurately remove.

You really cannot ignore the facts that I posted about rotor min thickness. Can a used rotor possibly have enough material left to turn while still keeping it above that minimum? Theoretically, yes. Practically, no.

A rotor just at minimum thickness is a rotor that is just ready for the trash.

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But that still in no way makes turning the rotors damaging. Does it?
Take a step back and examine what a rotor actually does.

A rotor's purpose is to be part of a heat management system... friction between rotor and pad is the conversion from kinetic to heat energy, which slows the car. THEN, the rotor's secondary purpose is to absorb that heat, and then dissipate it to the surrounding air. How much heat the rotor can safely store before dissipation is strictly a question of mass. By removing significant amounts of material, as with extreme wear or resurfacing, you are compromising the rotor's "heat sink" capabilities.


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I feel that turning the rotors makes the surface readily available for the pads to be bed in. Also so as to not cause irregular wearing and then cause problems. It's more preventive so that things don't become a problem.
You're not advocating a rotor resurface on a new rotor as a benefit, are you? The blanchard grinding of a new rotor surface as supplied by the manufacturer is the ideal "fresh" surface for all-new parts. It is as close to a perfectly flat plane as possible, critical for good pad bedding-in. Resurfacing produces an inferior finish.

I also hope you're not advocating a rotor resurface on a good used rotor either! A used rotor that has minimal runout and a smooth surface is even better, as you already have a seasoned surface with appropriate pad deposit. Remember that brakes generate friction between the pad and the pad material normally embedded in the rotor surface. This is why new (or resurfaced) rotors do not have the same feel or function as bedded-in brakes.

I think we discussed the other things already.


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Now had you just said that, we could have agreed long ago. It's something that CAN be done, May be done, but maybe not the most cost effective thing to do. But are you saying it's something that "Should Not Be Done?" If so then simply what is this safety reason??? That is all I'm looking for. Tell me the rotors explode, the pads shread, the lathe causes molelular changes that burn the metal and they can never bed-in correct again. Anything truthful why they Should Never be Turned, as I don't want to have injury or cause injury. But if it's just injury to one's wallet. That's not the answer I'm looking for and is not what was being discussed earlier.
Now had your answer earlier simply been "yes, I want to discuss whether this can be done theoretically, even though the arguments against it are insurmountable" the answer would have been "yes".

You should note that I did not say "cannot" be turned. I said "should not" because it's just plain pointless.

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... or I'll take off my trick UUC stuff and get Rogue stuff instead.
Then we can discuss what dumb things really are!

I'm always nice, you know that. But you can only twist the tiger's tail so far...


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But I'm still keeping the UUC hat(that MaxHat brand is the best hat I've ever come across).
Cool, huh? A lot more expensive that a generic hat, but such is the benefit of buying quality.

- Rob
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Old 01-25-2007, 03:41 PM   #32
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Originally Posted by Staszek View Post
Your other argument about not replacing the windshield when the wipers go or not throwing away the wheels when the tires go is a completely different thing.

The windshield is not consumable, neither are the rims (unless someone breaks or steals them) rotors are consumable and are meant to be eventually replaced.
Had you read that whole paragraph together, you would see I specifically listed it as an "extreme", and then listed things more in order with topic like fixing a flat on a new tire.
Please don't find things I've written out of context as you will be missing the point. And there was only one point to the post. That's all.
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Old 01-25-2007, 03:54 PM   #33
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Originally Posted by jbeurotech View Post
M models Must not be machined why do you think on the Hi perfromance car BMW sates this, is it possibale they know that turning rotors is a bad idea??
I've never questioned the not turning the M-rotors. They are usually different material and contruction. We know that ultra high performance cars have different braking needs and equipment. But if the "M-rotors must not be machined", where does that leave the non-M in that statement? Wouldn't they have said "ALL BMW rotors must not be machined", why specify M-models and not extend it to "ALL" models?
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Old 01-25-2007, 03:58 PM   #34
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Did you read the other article I posted it states why it is very hard to bed the pads after turning rotors, which is the main reason I will not do it along with the fact that most cars up here(MN WI MI) have so much rust in the vent holes that they do not dissipate heat any more and to take off more material can cause real problems, ALSO in the Delphi artical they talk about thinner rotors causing a lot of brake noise due to the harmonics most people fail to realize most brake noise is rotors not pads. With this in min the number one complaint with brakes is noise and I have to be wary of this complaint when I make recommendations to the customer.

Now my last point and yes I have performed this test. I have taken new pads and turned rotors and performed a stopping test.
then take same new in the box pads and new rotors and perform a stopping test.(make sure both sets are bedded the same.) The new rotors and pads will always out brake the turned rotors, also old rotors and new pads will always outbreak the turned rotors.

I like you am very sceptical and refuse to sell my customer on baloney so I will test and be sure of thing before I claim anything to my customers.

Good Luck!!
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Old 01-25-2007, 04:24 PM   #35
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Originally Posted by Rob Levinson * UUC Motorwerks View Post

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When that monetary value is taken out of the equation then it's a moot point. My only discussion is why they "Should Not Be Turned"???.
How about they often cannot be turned? How much material a resurfacing removes varies, but less than 1mm is beneath the smallest amount many of the lathes can accurately remove.

You really cannot ignore the facts that I posted about rotor min thickness. Can a used rotor possibly have enough material left to turn while still keeping it above that minimum? Theoretically, yes. Practically, no.

Now had your answer earlier simply been "yes, I want to discuss whether this can be done theoretically..." the answer would have been "yes".

You should note that I did not say "cannot" be turned. I said "should not" because it's just plain pointless.
I'm always nice, you know that.
Cool, huh? A lot more expensive that a generic hat, but such is the benefit of buying quality.
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It seems you answered exactly what I was asking and confirmed there is NO reason THEY CAN NOT BE TURNED and used. That is the only point I had continuously written/asked throughout this whole discussion.
*But there are better reasonings not to. Compelling is the small amount of metal that can be taken off. Thanks for your time.
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Old 01-25-2007, 04:32 PM   #36
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Originally Posted by jbeurotech View Post
Not quite, but there's definitely a trend toward replacement.

Here's why...
jbeurotech,
Thanks so much for providing and forwarding the info. It was exceptional reading and enlightening. I find it very compelling to your point to not choose to recondition/resurface rotors. Much appreciated for sharing and adding to the discussion. I know it has taken time out of your business day. Thanks again for your time
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Old 01-25-2007, 04:41 PM   #37
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Originally Posted by Alex323Ci View Post
Had you read that whole paragraph together, you would see I specifically listed it as an "extreme", and then listed things more in order with topic like fixing a flat on a new tire.
Please don't find things I've written out of context as you will be missing the point. And there was only one point to the post. That's all.
Your right my mistake, but I think you made the point of this post that you want people to say ok yes TECHNICALLY you can still turn rotors and it will work. Which TECHNICALLY is true, but TECHNICALLY I could use a rag as an oil cap, it would work for a while, but wouldnt be the best thing to do.

I think that is what the others have tried to point out to you but you just want to hear yes I can turn my rotors if I wanted to.

So yes you can still turn rotors.

That being said I have not turned a rotor in any of my last 4 cars for all of the reasons Rob and JBeuro have stated, its a waste of time and effort.
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Old 01-25-2007, 04:41 PM   #38
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No problem!! I like to be able to back up my statements! I rarely will give a statement without proof, or having proof ready so some smart ALEX call me out LOL
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Old 01-25-2007, 05:06 PM   #39
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Just to put in my $.02, during my stint as a tech at a Mercedes dealership several years ago we never turned rotors. If rotors looked good and were above minimums they simply got new pads. Unacceptable rotors were replaced entirely. The vast majority of the brake jobs done there were limited to throwing in new pads and sensors.
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Old 01-25-2007, 05:23 PM   #40
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Your right my mistake, but I think you made the point of this post that you want people to say ok yes TECHNICALLY you can still turn rotors and it will work. Which TECHNICALLY is true, but TECHNICALLY I could use a rag as an oil cap, it would work for a while, but wouldnt be the best thing to do. I think that is what the others have tried to point out to you but you just want to hear yes I can turn my rotors if I wanted to.

So yes you can still turn rotors.

That being said I have not turned a rotor in any of my last 4 cars for all of the reasons Rob and JBeuro have stated, its a waste of time and effort.
I don't think you have read the posts very intentively if you think that was the case. As I pointed out Bimmer and Roundel listed it being fine to do. The Bentley Manual tells of it. I and others have not had one problem with turning BMW rotors. I just wanted to know the reason Why they CAN'T. I don't know how you missed that, it's written numerous times. I don't do things simply because someone on the internet says so or BMW tells of Lifetime Fill gear Oil(don't get me started on that BMW statement). I like to know the reasons, call me crazy. But I have been given great reasons why one wouldn't want to. Good enough reasons for me.
If my discussion has given light to new facts about brakes on this Forum, then even better. This is an open forum and I feel I have more than held my own backing every one of my statements.
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