I think I have warped my rotors

When I apply the brakes I get a pulsating sensation and some vibration through the brake pedal.

Background. Changed from OEM brake pads to Axxis Ultimates about 2,000 miles ago, now have 30K. I embedded them per Dave Z. instructions then 2 days later took the car to a road coarse. So I am wondering if the new brakes pads were too much for the old rotors at the track.

Time for new rotors>

Originally Posted by Malachi

When I apply the brakes I get a pulsating sensation and some vibration through the brake pedal.

Background. Changed from OEM brake pads to Axxis Ultimates about 2,000 miles ago, now have 30K. I embedded them per Dave Z. instructions then 2 days later took the car to a road coarse. So I am wondering if the new brakes pads were too much for the old rotors at the track.

Time for new rotors>

Arent you still under factory maintenance with your '02? Couldn't you- I mean.. THEORETICALLY couldn't you drop those old stock pads in and have the rotors replaced under the maintenance plan? Just thoughts..

Originally Posted by PropellerHead

Arent you still under factory maintenance with your '02? Couldn't you- I mean.. THEORETICALLY couldn't you drop those old stock pads in and have the rotors replaced under the maintenance plan? Just thoughts..

Its a good thought, in that my dealership may do that for me anyway since they have installed all my Dinan stuff and may work with me. But in the end, I would rather keep my name clean rather than a couple of hundred bucks.

Sounds like warped rotors. When you swapped pads did you reface the rotors?

Originally Posted by Greco

Sounds like warped rotors. When you swapped pads did you reface the rotors?

Its my understanding that you don't reface or "turn" these rotor because they are mad of aluminum and not steel. So, no....

Wow... I hope they are not Aluminum!!! Aluminum loses about 30% of its strength at 400 degrees f. Not a good plan for brakes. However, even though they are steel, it is a true statement that our rotors should not be resurfaced/turned. Typically, the rotors are at or beyond the wear indicator before they start to warp anyway. Your situation may be different but I woudl be willing to bet that if you had them turned to remove the warp, it would take them below the wear indication mark.
My $.02...
JB

Originally Posted by DSPTurtle

Wow... I hope they are not Aluminum!!! Aluminum loses about 30% of its strength at 400 degrees f. Not a good plan for brakes. JB

Well, thanks for clearing that up. It was my understanding that these rotors did not get re-surfaced and that they were more of a throw away when worn product, so I made a bad assumption.

Again, thanks for clearing that up so no one else runs around with bad information.

How much does it cost when you take your car for full maintainance.

Originally Posted by bmw540i

How much does it cost when you take your car for full maintainance.

I think it has been free to this point.

Originally Posted by Malachi

I think it has been free to this point.

What if you dont have free maintainance anymore how much do you guys think it will cost to do a full check up.

There a a lot of opinions on what causes rotors to warp. Some say excessive heat. Others say heat and then cold water on them may cause warping.

I personally do not like turning the rotors. Especially if too much metal has to be removed due to the amount of warping. My opinion is that the thinner the rotor, the more likely it may warp again.

Typically, I just buy new rotors. Yes, it is more expensive than turning them, but not overly expensive. There are some aftermarket rotors that not only meet, but exceed the original equipment specifications. And are less than the ones from BMW. You may be able to find a source that provides them from the same manufacturer.

It can be a fairly simple DIY job, depending on your level of skill and experience. Most certainly does not require a BMW dealer expertise and expense.

The above is strictly an opinion. Possibly worth no more than it costs.

Van

P.S. Forget the above if it is still covered by warranty. Good luck!

Originally Posted by Malachi

Its my understanding that you don't reface or "turn" these rotor because they are mad of aluminum and not steel. So, no....

They aren't aluminum. They are iron. There is very little metallurgical difference between rotors from BMW, Mercedes, Brembo, Zimmerman, StopTech, etc. The manufacturers play around a little bit with impurities (e.g., phosphorus) to trade off characteristics such as hardness for susceptibility to pad deposition. But all mainstream rotors are made from what is called gray iron.

There have been repeated attempts to use aluminum alloys in rotors to reduce weight, the latest being something called metal matrix rotors by a company called CoolTech. But at high temperatures, even temperatures that could be experienced on the street, the coefficient of friction dropped dramatically, making them unsafe.

Originally Posted by Malachi

When I apply the brakes I get a pulsating sensation and some vibration through the brake pedal.

Background. Changed from OEM brake pads to Axxis Ultimates about 2,000 miles ago, now have 30K. I embedded them per Dave Z. instructions then 2 days later took the car to a road coarse. So I am wondering if the new brakes pads were too much for the old rotors at the track.

Time for new rotors>

The Axxis Ultimate pads are NOT track pads. What happened is that you were good enough at the track to drive those pads above 1200 degrees F and they began to leave uneven deposits on your rotors.

You don't have warped rotors, you have a thickness variation across the face of them. You should be able to see dark gray, uneven streaks across the friction surfaces. If you were to take them off the car and measure in about 15 - 20 places around the circumference, using a micrometer, you would find thickness differences on the order of 0.0005". That's an order of magnitude less than the runout ("warping") required to notice a pedal puslastion under braking of about 0.006".

There are a few ways you could fix this:

1. Get some "garnet" paper from a hardware store and attempt to remove the deposition layer from the rotor surface. Sandpaper has aluminum oxide and will react with the iron under heat, ruining the rotors. You MUST use garnet paper.

   
   

2. Take the rotors to a shop and have them turned, only removing as much as required to get the deposition off. We're talking about less than half a thousandth.

   
   

3. Replace the front rotors.

Next time you go to the track, use a set of Hawk HT10 race pads in front. The Axxis Ultimate are fine in the back. Install the HT10 pads, then drive around on the street long enough for the abrasive race pads to chew away the transfer layer left behind by the street pads. Then, bed the HT10 pads in and do your track event. After the event, drive around for a while until the HT10 pads chew away their own transfer layer. Then install and re-bed the street pads. This technique will ensure that you will be vibration free, both during and after your track events.

You don't want to install the track pads at the track, then bed them in on top of the transfer layer from the street pads! Otherwise you will have vibration problems when you get the brakes heated up past 1200 degrees.

The track pads run in an abrasive mode when cold. Once heated, they are more adherent mode and will lay down a transfer layer, just like a street pad. But if you drive around with them on the street, they will quickly chew away that transfer layer and then begin to grind away at your rotors. Leave them on your car for a couple of weeks and you'll be getting new rotors!

Originally Posted by DZeckhausen

[*]Take the rotors to a shop and have them turned, only removing as much as required to get the deposition off. We're talking about less than half a thousandth.

[*]Replace the front rotors.[/list]

Holy smokes! Are you saying our E39 OEM rotors can be turned? I have heard it more than once that these rotors cannot be turned.

So I have two options, have them turned or use garnet paper.

edit, 3rd option is to replace the front rotors.

Originally Posted by Malachi

Holy smokes! Are you saying our E39 OEM rotors can be turned? I have heard it more than once that these rotors cannot be turned.

So I have two options, have them turned or use garnet paper.

edit, 3rd option is to replace the front rotors.

I was told by BMW master techs that it was there practice to not turn factory rotors and that ususally a set of factory rotors would last through 2 sets of pads with normal driving use. Maybe this was just the dealers decision handed down to the techs but, because they're not that costly the decision to swap them makes sense.

Like Dave says you may want to switch pads when ur tracking. If your going to track often this might become a pain and going with a higher end street or lower end racing rotors and pads might be an option.

There are numerous types of rotors out there as others have expressed. There are also aluminum or teflon coated aluminum rotors and what MBZ calls scrolling aluminum rotors plus ceramic, iron, etc.

At any rate hope you had a great time on the track and did the resonator swap help at all out there?

Originally Posted by Malachi

Holy smokes! Are you saying our E39 OEM rotors can be turned? I have heard it more than once that these rotors cannot be turned.

So I have two options, have them turned or use garnet paper.

edit, 3rd option is to replace the front rotors.

Sure they can be turned! You've got 1.6mm of allowable wear. If you take a couple thousandths of an inch off both sides, you can turn the rotors 16 times before you've removed enough material to have to replace them.

That being said, the BMW rotors are on the thin side when compared to other manufacturers. For example, Mercedes allows 2.4mm of wear before the rotors are replaced.

In general, I am against turning rotors because it's a procedure that is way overdone and often done poorly. Some people are of the mistaken belief that you NEED to turn rotors when swapping pads. This is not the case, unless you have a serious deposition issue (like yours!) or if your rotors have deep grooves in them. When turning rotors for deposition, you want to remove the least possible amount of material, since the deposition is on the order of several ten-thousandths of an inch thick.

A major problem with turning rotors is that some shops are so careless with the maintenence and set-up of their equipment that they can easily introduce several thousandths of runout simply by being careless. Don't take your rotors to Pep Boys where some kid is going to throw them on the brake lathe without checking that they are properly fastened to the fixture and then set the machine to rip off a huge hunk of material and just walk away. There's a reason Pep Boys charges only $5/rotor to do this.

In general, replacement rotors from Brembo, Balo, ATE, or Zimmerman are so inexpensive that it makes more sense to just slap new ones on.

Originally Posted by DZeckhausen

Sure they can be turned! You've got 1.6mm of allowable wear. If you take a couple thousandths of an inch off both sides, you can turn the rotors 16 times before you've removed enough material to have to replace them.

That being said, the BMW rotors are on the thin side when compared to other manufacturers. For example, Mercedes allows 2.4mm of wear before the rotors are replaced.

In general, I am against turning rotors because it's a procedure that is way overdone and often done poorly. Some people are of the mistaken belief that you NEED to turn rotors when swapping pads. This is not the case, unless you have a serious deposition issue (like yours!) or if your rotors have deep grooves in them. When turning rotors for deposition, you want to remove the least possible amount of material, since the deposition is on the order of several ten-thousandths of an inch thick.

A major problem with turning rotors is that some shops are so careless with the maintenence and set-up of their equipment that they can easily introduce several thousandths of runout simply by being careless. Don't take your rotors to Pep Boys where some kid is going to throw them on the brake lathe without checking that they are properly fastened to the fixture and then set the machine to rip off a huge hunk of material and just walk away. There's a reason Pep Boys charges only $5/rotor to do this.

In general, replacement rotors from Brembo, Balo, ATE, or Zimmerman are so inexpensive that it makes more sense to just slap new ones on.

Excellent info Dave!

I agree with Dave that you do not have to turn rotors unless they are grooved and then I would replace them. I have been doing my own brake jobs for the past 30 years and never had to turn a rotor. If they were within the thickness spec., I just sanded them with emery cloth to provide a new abrasive surface for the new pads to seat against. Never had a problem doing this on a wide variety of cars.

I also used this technique on drum brakes as well.

Steve D

Originally Posted by Steve D

I agree with Dave that you do not have to turn rotors unless they are grooved and then I would replace them. I have been doing my own brake jobs for the past 30 years and never had to turn a rotor. If they were within the thickness spec., I just sanded them with emery cloth to provide a new abrasive surface for the new pads to seat against. Never had a problem doing this on a wide variety of cars.

I also used this technique on drum brakes as well.

Steve D

What is so taboo about having the rotors turned? It seems to be as much work and cost less than new ones. What am I missing?

On turning or not turning rotors: Brake rotors are manfactured on CNC machines that cost 100s of 1000s of dollars. Specs are held to about .003 inch. The process includes straddle cutting the rotor, double disc grinding and balancing. I worked with a company in California that manufactured about 100,000 rotors per month, so I am familiar with the process (I also spent about a year with Brembo). Bottom line: out of the box, a new rotor is ready to install (after washing) and needs no machining, nor should it be machined (many mechanics still machine new rotors before installing).

Turning a rotor on a $3000 Aimco lathe in the back of a dirty machine shop or installation shop is NOT going to produce the same parallelism, finish and accuracy! For sensative brake systems (Ford calls these 'Tuning Fork brake systems') the runout that would be introduced by these inferior and often worn machines will manifest as vibration and/or pedal pulsation. Most lathes have at least .001 runout on the shaft, with no weight. Add the various cones and adapters (which are usually worn) along with the rotor and that runout can easily be .010. I call this the train wreck, with all the various adapters and the rotors cinched together on the lathe.

This is OK for an older vehicle, something less sensative perhaps, but it will drive you crazy on a BMW (or any German car, Volvo, Saab, for that matter). In Europe, brake rotors are sold in pairs, packaged 2 to a box. Not only do they replace the rotors, but they do it in pairs.

Originally Posted by Steve D

I just sanded them with emery cloth to provide a new abrasive surface for the new pads to seat against.

I've done the same thing with Emery cloth, but now I'm concerned about***********:

Originally Posted by DZeckhausen

Get some "garnet" paper from a hardware store and attempt to remove the deposition layer from the rotor surface. Sandpaper has aluminum oxide and will react with the iron under heat, ruining the rotors. You MUST use garnet paper.

So, Dave Z. what say you about Emery cloth? Its not "sandpaper", but will its components react with the iron under heating?

Originally Posted by DZeckhausen

In general, replacement rotors from Brembo, Balo, ATE, or Zimmerman are so inexpensive that it makes more sense to just slap new ones on.

So you are saying that the above rotor manufacturers are about the quality and cost?

Do anyone of them look better than the other or are they your basic looking rotors? Looking for a tie breaker.

Originally Posted by Dan540

Turning a rotor on a $3000 Aimco lathe in the back of a dirty machine shop or installation shop is NOT going to produce the same parallelism, finish and accuracy! For sensative brake systems (Ford calls these 'Tuning Fork brake systems') the runout that would be introduced by these inferior and often worn machines will manifest as vibration and/or pedal pulsation. Most lathes have at least .001 runout on the shaft, with no weight. Add the various cones and adapters (which are usually worn) along with the rotor and that runout can easily be .010. I call this the train wreck, with all the various adapters and the rotors cinched together on the lathe.

Now combine this crummy, out of spec machinery with a chain like Pep Boys that hires kids to turn rotors for $5/each without giving them any training, and you get rotors that are far worse off than when you started.

I only trust a handful of people to turn my rotors. One of them is Steve D'Gerolamo at Ultimate Garage:






You won't find such nice equipment and such attention to detail at most other places.

Originally Posted by Malachi

So you are saying that the above rotor manufacturers are about the quality and cost?

Do anyone of them look better than the other or are they your basic looking rotors? Looking for a tie breaker.

The above are all very high quality. I would just grab the one that is available and/or costs less.

There are also some Asian foundaries that produce top quality rotors, but it's more difficult to figure out which are good and which are not. Dan540 is president of Centric, a massive brake wholesaler in California, and he supplies quality Asian rotors to retailers around the country. We're lucky to have such a key industry insider right here on the Bimmerfest board!

Thanks! Just here to learn and help where I can.