Ok, I have been having some vibration while braking (warped rotor like) and I took the car to a brake shop. I was told the rotors had stress fractures... the mechanic stated that these usually occur of the car sat for a long period of time or excessive heat. He stated that there were "heat spots" on the rotors.....

Never had this happen nor did I know it could on a street car. Now I could understand if I used the car on the track, which I do not... I am not hard on brakes as my car is two years old and I am about to turn 50K miles with the mintek pads I put on at 10K miles... most of my driving is highway (80+ in the mornings and sto pand go in evenings).

Is this possible? Is it probable?

 

You got 50k out of a set of rotors? Count yourself lucky. The rotors are as soft as the pads. On most BMW cars, if the pads are worn down, the discs are probably below spec and need replacing. I get about 30k out of a set of pads and rotors, but I use the brakes as hard as I use the throttle.

 

My pads still have a significant amount left- 70-80%. I drive fast but not aggressively so I am not on the brakes that much

 

Joel, your rotors may be below spec now if you have 50K on them! Are they the regular OEM or JCW? I can't remember!

 

The regular OEM with the Mintek pads pads I put on shortly after getting Percy.

If you look at the rotors (which have never been turned) they seem slightly worn- there is an ridge where you can see where the pads sit and the orginal thickness of the rotor... it is visible and you can feel it but it too small to measure... go figure...

Something else the mechanic said was there were "heat spots" never heard of them...

 

If you are braking from a high speed and come to a stop for an extended period (example. slowing down from 80+ mph to a red light at an off ramp), your hot pads and rotors are clamped together at the same spot for as long as you are sitting there. That's one way for a street car to develop heat spots or warp your rotors. If you are on level ground while stopped, take your foot off the brake. Otherwise, let the car roll back a bit (provided nobody is close behind you) so the pads aren't in the same spot... You can also use the parking brake (don't do this if you've been road racing or the brakes are EXTREMELY hot) to hold yourself still.

 

Hmmm, so my 90 MPH trip for 36 miles to a red light on a steep decline is a very bad thing.....that is my morning commute where my drive home is stop and go.

 

It's not a "bad thing" but man I wish I could get Dan00Hawk to explain that to some of my automatic tranny car customers....! "I thought buying a BBK would prevent me from having these problems." Never mind the fact they bring some 4000lb car to a quicker stop from higher speeds now. And still have the same bad habits. grrrr.

 

Is it possible? Yes.

Is it probable? Maybe. It's at least feasible as Myth Busters would say.

Anytime there is heat build up then there can be stress on the rotors and when this happens over time due to long steep down hill braking or high speed track lapping then it's fairly easy to wear out rotors.

In fact even good rotors like PowerSlot rotors can be damaged in one day of track use.

If you are not particularly hard on your brakes, don't ride them, and go up and down hills a lot then you shouldn't be any more prone to this than the rest of us who don't crack rotors.

So how hard are you on your brakes and who else drives your car?

 

I'd suggest coasting down to 60-70-ish and slowing more gradually for the light, and then not keeping your foot on the brake pedal while waiting for the light if you can help it. This would certainly help prevent any "hot spotting" that may otherwise occur. It's not a bad thing to slow from high speeds if you can give your brakes a chance to cool. But no air flow while you are sitting still doesn't help anything.

 

Stress cracked rotors with the way you desribe your driving and mileage? Strange. It has happened to me with one of my road racing motorcycles, but they were old and used very hard.

 

If you can feel that ridge with your fingernail (wait til the rotor cools) the rotor thickness is below spec. BMW has set specs that will allow no rotor turning whatsoever.