[zx10guy]

Originally Posted by kring

HAAHAHAHAH…. So funny, yuk yuk.

What do you think a squeal is? Please share an explanation of what’s happening that produces that noise.

The squealing is from the brake pads contacting the various parts of the brake caliper. This is why many brake pads come with an anti-squeal shim on the back of the brake pads to help absorb the micro vibrations that can occur when the brake pads contact the rotors.

In addition to the anti-squeal shims on the brake pads, the use of anti-squeal compound can also stop the squealing which is applied to the back of the pads.

I've never had to use anti-squeal compound and just rely on the anti-squeal shims that come with the brake pads. But I also take one extra step where I lubricate the ears of the pads where it sits in the calipers or other contact points depending on how the brake pads are mounted with high temp caliper grease that are normally used for the caliper sliders/guide pins.

The squealing is NOT from harmonic differences between the rotor and brake pads.

[david in germany]

Originally Posted by kring

Depends on age/miles of the rotors, they key is being in spec. BMW Recommends in their technician manual to resurface if there is enough rotor to do and keep in spec.

However, it ALWAYS best to replace both at the same time, but as you pointed out it cost a bit more. This will give you the best performance, life and quiet stable braking for another pad lifetime.

Rotors develop a resonant frequency and that marries the pads as they break in together. Quite often a resurfaced rotor and a pad will not develop into a harmonic match and you will forever have brake squealing, the degree depends on how harmonically they are out of sync. Or you may get lucky and they align. I have turned maybe 10 sets of rotors in my life and I’d say only twice it worked out perfectly… the rest either had squeal, relatively quickly they developed uneven stopping or accelerated wear.

If you can get them turned for nothing, you could try it.. but keep in mind that id its a bust, you may now be out another set of pads if you have to go for the full rotors the second time. You wouldn’t want new rotors with used bedded pads. Could you? Of course you “could” do that… but you might as well trade the S4 in for a prius at that point.

Give your car the love that it gives you and do a proper brake job on it.

Just lol…
Can you provide a copy and paste of said tech manual?
I have never EVER seen ANY BMW dealer / official garage that would resurface a rotor. It is not cost effective for them to take the time to do it. A BMW mechanic would simply check the minimum thickness and slap pads on the car if they were at or thicker than the minimum unless there is any damage visible to the rotor surface. It is the service advisors job to sell more parts therefore they will always try to upsell the parts once out of their cost.

Squealing comment… uh, ok.. addressed correctly a few times above.

Harmonic mismatch…. if you have surface contact you have friction, friction means stopping ability.

[kring]

yes, but only because you are such a confident ass who needs to be put in his place.

SIB numbers 34 01 14 and 34 10 16

and what do you think the vibrations are? they can form into harmonic vibration (like a wine glass with water). and based on the properties and conditions that can change and not match the other sounds of the brakes/wheels. Each piece of metal in the world has a harmonic frequency, like a tuning fork... if you tap on a piece of metal it has a sound that doesn't change. frequency is measurable and there can be a mis-match.. why do you think there are shims and compound? they are there to counter the harmonic vibrations. so laugh all you want, believe whatever you want.. but you should really keep your stupidity and rudeness from being directed at others.

[Mandi90TT]

Originally Posted by kring

yes, but only because you are such a confident ass who needs to be put in his place.

how ironic.

[david in germany]

Originally Posted by kring

yes, but only because you are such a confident ass who needs to be put in his place.

SIB numbers 34 01 14 and 34 10 16

and what do you think the vibrations are? they can form into harmonic vibration (like a wine glass with water). and based on the properties and conditions that can change and not match the other sounds of the brakes/wheels. Each piece of metal in the world has a harmonic frequency, like a tuning fork... if you tap on a piece of metal it has a sound that doesn't change. frequency is measurable and there can be a mis-match.. why do you think there are shims and compound? they are there to counter the harmonic vibrations. so laugh all you want, believe whatever you want.. but you should really keep your stupidity and rudeness from being directed at others.

So, the answer to my question is, no. You can’t provide a copy and paste of said technical manual mentioning resurfacing of the rotors.. SIB is not a tech manual.

34 01 14 Discuses absorber pads on the M5 and M6 vehicles.

34 10 16 <~ I stand corrected. But also very specific to rotors with damaged surfaces (in bold on the SIB) as my statement above says.
AND It is also specific that it is done only in conjunction with;
A. The service is related to a customer complaint.
B. The car is in for a free service/inspection

So if you are paying for the repair/ service, BMW WILL recommend new rotors and WILL NOT resurface the old ones.

So it is true in my statement “it is NOT cost effective” for BMW to resurface rotors if you are paying for it.


And bottom line, reading is very important.

[david in germany]

On a trciary note, oncar lathes are pretty damned cool. Too bad I can’t justify one for my tool box…

[kring]

This has become a weird discussion, I think you took a left on your crusade and are arguing points I din’t think were disputed. I certainly don’t dispute the cost effectiveness, the recommendation by BMW or that it’s best to replace the rotors as recommended by BMW. From the beginning I clearly and only recommended a full replacement to the OP..

I have no idea how to respond to your post.

[david in germany]

Originally Posted by kring

This has become a weird discussion, I think you took a left on your crusade and are arguing points I din’t think were disputed. I certainly don’t dispute the cost effectiveness, the recommendation by BMW or that it’s best to replace the rotors as recommended by BMW. From the beginning I clearly and only recommended a full replacement to the OP..

I have no idea how to respond to your post.

Maybe by apologizing for calling me an ass? Not once did I take my comments to a personal level.

I did state facts and even in my post above stated that you corrected me on something. I kept my post professional. Something you really should learn to do if you plan on frequently posting here.

[BMWCCA1]

I work at a BMW dealership and we have a portable on-car brake lathe for resurfacing rotors, particularly those that will not pass inspection due to rust. It is quite common at BMW dealerships so I'm not sure where this discussion took such an ugly turn.

[david in germany]

Originally Posted by BMWCCA1

I work at a BMW dealership and we have a portable on-car brake lathe for resurfacing rotors, particularly those that will not pass inspection due to rust. It is quite common at BMW dealerships so I'm not sure where this discussion took such an ugly turn.

Nice to know. Out of curiosity, how often do you guys actually use it?

It took an ugly turn because of personal insults.

I personally love to learn new information. If I am wrong about a subject, give me correct info and I am happy but some people in these days resort to personal insults and think that it makes them look better.

[BMWCCA1]

Originally Posted by david in germany

Nice to know. Out of curiosity, how often do you guys actually use it?

Well, it doesn't get used on new cars under the BMW Maintenance Program Extension because that covers pads and rotors. But I do see it being used usually once a day. It's on a cart on wheels and moves from one shop to the other. Our techs (maybe a dozen of them—depending on departures and Covid) are in two different buildings. Our SHP Inspection officers are tough on rust on brake rotors. The code is a bit vague and we'll often fail a car and the customer will immediately take it to another inspection station that laughs at us and then passes the car, but our State Police Inspection Officer has always agreed with our decision when asked by a customer to question our failing their car. The machining is often a less-expensive way to comply with the inspection code.

[david in germany]

Originally Posted by BMWCCA1

Well, it doesn't get used on new cars under the BMW Maintenance Program Extension because that covers pads and rotors. But I do see it being used usually once a day. It's on a cart on wheels and moves from one shop to the other. Our techs (maybe a dozen of them—depending on departures and Covid) are in two different buildings. Our SHP Inspection officers are tough on rust on brake rotors. The code is a bit vague and we'll often fail a car and the customer will immediately take it to another inspection station that laughs at us and then passes the car, but our State Police Inspection Officer has always agreed with our decision when asked by a customer to question our failing their car. The machining is often a less-expensive way to comply with the inspection code.

I can believe that. If it is pretty, it will pass.
Thanks for your follow up!

Just wanted to add, it seems to have nothing to do with functionality but to appease the troll under the bridge.

[chowser51]

Depends. On my f33 with base brakes I did the rear rotors and pads at 48k. Might as well. If was easy to do. Did the front pads and rotors at 60k and a brake fluid flush. Easy and cheap to do at home.

On my f39 with M brakes, replaced the front pads at 25k. Well bmw did for free. They didn’t touch the rotors.

[5.M0NSTER]

I’ve gone through 3 sets of pads on my M2 with a single rotor, and about 7 track days. When I went in for service at the dealer, they said rotors still had plenty of thickness. They were pretty cracked, but still thick enough.

Go by remaining thickness, and if it’s only 1 set of pads you went through, I’d definitely check before replacing.

[TheWatchGuy]

i only replace rotors if they need it. whether from being below spec thickness to deep damage on the face.

a lot of places recommend replacing rotors with pads, since a lot of oem rotors are starting to be thinner than they used to be, but as long as you are within the tolerances, no issue.

[ShocknAwe]

I never replace rotors until they're spent, and resurfacing is a waste of money IMO, just throw on some track pads do a few hard stops and put your new street pads in, bed them, and you're gtg.

What a pile of malarkey. How much wasted money does a new set of rotors every pad change come out to?

[eseny]

Originally Posted by kring

Depends on age/miles of the rotors, they key is being in spec. BMW Recommends in their technician manual to resurface if there is enough rotor to do and keep in spec.

However, it ALWAYS best to replace both at the same time, but as you pointed out it cost a bit more. This will give you the best performance, life and quiet stable braking for another pad lifetime.

Rotors develop a resonant frequency and that marries the pads as they break in together. Quite often a resurfaced rotor and a pad will not develop into a harmonic match and you will forever have brake squealing, the degree depends on how harmonically they are out of sync. Or you may get lucky and they align. I have turned maybe 10 sets of rotors in my life and I’d say only twice it worked out perfectly… the rest either had squeal, relatively quickly they developed uneven stopping or accelerated wear.

If you can get them turned for nothing, you could try it.. but keep in mind that id its a bust, you may now be out another set of pads if you have to go for the full rotors the second time. You wouldn’t want new rotors with used bedded pads. Could you? Of course you “could” do that… but you might as well trade the S4 in for a prius at that point.

Give your car the love that it gives you and do a proper brake job on it.

King, your comment about squeaking and resonant frequency is something most readers will ignore, and in this thread, unfortunately dismiss. There is no doubt this is what is going on. Appreciate the time you took to share your great insight.

[Efthreeoh]

Originally Posted by ShocknAwe

I never replace rotors until they're spent, and resurfacing is a waste of money IMO, just throw on some track pads do a few hard stops and put your new street pads in, bed them, and you're gtg.

What a pile of malarkey. How much wasted money does a new set of rotors every pad change come out to?

About $140 (front) and $100 (rear) for my E90 at each 100,000-mile brake change (because the rotors last all the way through the 2nd set of pads ). I offset it by (a) my DIY labor, and (b) following BMW's extended oil drain intervals.

[Captain Blood]

Originally Posted by ShocknAwe

I never replace rotors until they're spent, and resurfacing is a waste of money IMO, just throw on some track pads do a few hard stops and put your new street pads in, bed them, and you're gtg.

What a pile of malarkey. How much wasted money does a new set of rotors every pad change come out to?

$1400