New pads and rotors -- "whirling" sound when braking?

[tgb1974]

Originally Posted by M3SQRD

tgb1974

I’m glad to hear the noise and brake pedal feel issues are resolved!

I’m not surprised to hear it was due to the winter tires based on my own experience with them. I’d have your alignment checked ASAP. If your alignment is off, it could have been wearing one tire, or one side, differently from the others so your issues continued to worsen as you drove more on the winter setup.

Remember, it’s ultimately the tires that stop a car. So what the tires are doing as you brake can be felt in the brake pedal. Winter tires have much taller, softer tread blocks as well as more smaller blocks (increase channeling and ability to dig into snow) so they squirm around a lot under braking. If, for example, the left and right fronts are wearing differently due to the left-right alignments being different, the car may want to pull to one side while braking or it’s a combination of tire wear and alignment.

A five year old tire is likely still fine if it’s been stored properly, has sufficient tread and is showing no signs of dry rotting. Rubber tends to harden with age and it results in loss of grip. As long as the tires aren’t showing any of these signs then they’re likely safe to use. There’s no real “expire by” date on a tire; however, the older they get, the lower their performance window.

Thank you for this detailed and helpful analysis. I did not realize that what the tires are doing as you brake can be felt in the brake pedal. As I mentioned, the dealer's lead M technician inspected my car and found nothing wrong with the brakes, rotors or control arms, He also inspected my winter tires and thought they looked fine. In terms of alignment, the car no longer jerks while braking or anything like that. The car, in short, drives like a dream now!

[tgb1974]

Originally Posted by robbo mcs

Some tires, with particular tread patterns, can definitely make noises like you describe while braking. I've experienced it with some semi-slick race tires

I did not realize this. Thank you. The winter tires I have been running are the Michelin Pilot Alpin PA4 model, which are specifically designed for high performance vehicles, so you would think that they would not cause all of these anomalies!

[tgb1974]

Originally Posted by mapster37

There is a BMW service bulletin that describes the exact noise you are concerned with. It's 100% completely normal operation. It should get less noticeable with more miles driven.

Do you happen to have a link to this service bulletin or its number? Thanks!

[M3SQRD]

Originally Posted by tgb1974

Thank you for this detailed and helpful analysis. I did not realize that what the tires are doing as you brake can be felt in the brake pedal. As I mentioned, the dealer's lead M technician inspected my car and found nothing wrong with the brakes, rotors or control arms, He also inspected my winter tires and thought they looked fine. In terms of alignment, the car no longer jerks while braking or anything like that. The car, in short, drives like a dream now!

I’m just glad everything has worked out in the end. At least when you change the front rotors and pads, you’ll know what to expect as the pads and rotors are bedded. It’s always a great feeling when you reinstall your summer wheels and tires! However, using the correct tires for the correct season is the way to it. Summer tires at temps <= 40 F can be quite challenging especially with a little rain on the roads.

[M-SJ3]

Originally Posted by M3SQRD

It’s best to bed-in the brakes to ensure you don’t over heat them, for example in an emergency stop, and the brakes decelerate the car properly. Other concern is if you get the brake pad too hot too quickly, you can glaze the brake pad (make the surface look polished like a mirror) and then the pad doesn’t stop or perform as well. There’s two types of braking - ablative and abrasive. Ablative is the way a properly functioning brake system should work. It starts by bedding-in the brakes which basically means you’ve transferred a uniform layer of brake pad material to the surface of the rotor. Once this happens, the braking actually occurs between the brake pad material and the pad material on the rotor surface that’s getting wore off, hence the name ablative braking. Abrasive braking is when there’s no transfer layer and if the pad is aggressive enough, say a track or high performance pad material, it actually wears away the surface of the brake rotor similar to a brake lathe and, thus, the name abrasive braking.

So to properly bed-in your brakes:

1. Drive and brake moderately (say ~30-40% of brake capability) for about 15-20 minutes to get good temperature into the rotors and pads.

2. In quick succession, brake from 50 mph to 20 mph with ~70-75% braking capability, repeat 3-4x times. Accelerate quickly back to 50 mph and perform the next braking attempt until you’ve done it 3-4x.

3. Same as #2 but get up to 65-70 mph and brake with around 90-95% brake capability without engaging abs to 20 mph. Again repeat 3-4x times in quick succession. Don’t wait more than five minutes before completing step 2 and starting step 3.

4. Drive on the highway, freeway, etc. for 10-15 min without applying the brakes (or if you do, try to keep it moderate and release the pedal as quickly as you can). This step is done to ensure the brakes cool uniformly and to allow the pad material to cure uniformly onto the rotor surface. If you followed these steps, your rotors will have a slightly darkish grayish color on the rotor surface (see below).

If you’re comfortable with braking without engaging abs, steps 2 and 3 can be combined into 1 step: essentially step 2 but get up to 70-75 mph and brake with 90-95% brake capability (no abs engagement) down to 20 mph. Repeat in quick succession 5-6x and then proceed to step 4 for the cooldown/curing. It’s a lot simpler to do than it might sound.

The earlier pics you posted of the rotors looked fine (no hot spots/bluing of the rotor surfaces) but they lacked any pad transfer.

Thank you for the detailed and well-written instructions! I really appreciate it.

Will give this a go over the weekend and make sure I find a decent highway to complete this on when nobody's on the road.

[mapster37]

Originally Posted by tgb1974

Do you happen to have a link to this service bulletin or its number? Thanks!

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