Strangest Brake rotors...

[Alexlind123]

So i took my wheels off for a routine inspection, and to investigate a shudder on braking at all speeds. Note that this shudder is NOT the shimmey assosiated with worn thrust arm bushings. I replaced those once, and this feels much different.

The brake rotors are PERFECTLY smooth to the touch, both across the rotor and around. There is absolutely no grooving or ridges on the sides or anything. They are also smooth in appearance, even more so than these pictures show.

I have never seen a brake rotor with anything even resembling this. Glazing came to mind when i saw it, but i dont even really know what glazing is, it was just the only thing i could think of that might describe this weirdness.

So, can anyone tell me what this might be?

http://servo.postverket.us/alex/rotor1.jpg

http://servo.postverket.us/alex/rotor2.jpg

The odd section is smooth and flush with the rest of the rotor. I have not used a dial indicator to check for runout.

[Blitzkrieg Bob]

it's a perfect image of the Virgin Mary.

[aston_jag_tech]

Is the screw holding the rotor to the hub secured?? I ran into a shimmy from that.

[attack eagle]

So i took my wheels off for a routine inspection, and to investigate a shudder on braking at all speeds. Note that this shudder is NOT the shimmey assosiated with worn thrust arm bushings. I replaced those once, and this feels much different.

The brake rotors are PERFECTLY smooth to the touch, both across the rotor and around. There is absolutely no grooving or ridges on the sides or anything. They are also smooth in appearance, even more so than these pictures show.

I have never seen a brake rotor with anything even resembling this. Glazing came to mind when i saw it, but i dont even really know what glazing is, it was just the only thing i could think of that might describe this weirdness.

So, can anyone tell me what this might be?

http://servo.postverket.us/alex/rotor1.jpg

http://servo.postverket.us/alex/rotor2.jpg

The odd section is smooth and flush with the rest of the rotor. I have not used a dial indicator to check for runout.
That looks very much like the leading edge of a pad impression, maybe someone overheated the brakes at some point (break in maybe?) and held the pedal down at a stop (automatic car?)... instead of slow rolling the last 5-10 feet and then e braking to stay stopped but off the brakes so they could cool evenly.

Try having them turned, and if that doesn't work toss em for new ones and break them in properly. It almost looks like the metal in that area is now different than that of the rest of the rotor

[bill g]

If you want to know too much check this link posted by Shogun a while back -
http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml#

Also check for variations in thickness of disk. Rotors on our E36 325 had variation of only .0016" - had rotors turned, problem fixed.

Bill G

[Alexlind123]

I guess i should have them turned, but how do i prevent it from happening again?

[BillionPa]

cryo treated rotors and ceramic pads.

[Jehu]

cryo treated rotors and ceramic pads.

Do you need to follow that bedding method if you Cryo your rotors and use ceramic pads?

[BillionPa]

kind of. the rotors and pads are still "raw" on the surface and need to be smoothed out.

my bedding period is as follows:

put the pads in the oven for an hour to remove any moisture and slowly outgass them. (not necessary, but i also used engine block paint on the caliper side and wanted it 100% dry). let them completely cool.

install rotors and pads.

make sure guide bolts are clean and properly torqued.

BLEED BRAKES (will provide more even brake pressure and prevent brake fade during bedding)

drive car around with gentle brake usage, so the pads and rotors are smoothed out without heating them up too much. once the rotors look coated with pad material over the entire rotor surface you are ready to do the bed in procedure. dont let the brakes heat up during this phase, and try not to come to a complete stop.

do the bedding procedure on a long deserted highway or country road, or at a track, as you do NOT want to stop, or be impeded from performing the procedure half way.

medium pressure = 4s to go from 60-30, heavy pressure = 20% pedal pressure away from ABS lockup or loss of traction, light pressure = noticable slowdown, if you were 6 car lengths away and some guy started to slow down and you were speed matching.

step 1: 60mph-30mph medium pressure, 10 sets, this will remove the uneven pad material from the rotor without letting it get too hot and baking it in there, while still getting the rotors hot.

step 2: 70-20 heavy pressure, 8 sets, this should induce some brake fade after about 6 sets. if you dont get brake fade thats ok.

step 3: get up to 70, then apply light brake pressure while maintaining that speed for about 60s, then no brakes and staying at that speed for another 60s.

step 4: 60-30, medium pressure, 5 sets

step 5: 70-20, heavy pressure, 4 sets

step 6: repeat step 3, but go for 2 more mins with no brakes at about 40mph to get the rotor temp down to normal operating temp.




the bedding procedure is to get the pad to rotor interface as close as possible and leave a pad layer on the rotor. this also heat cycles the rotor and removes resins from the pad compound (they should smoke!). cryo rotors are pre heat cycled, but still have a raw surface and need the best pad interface possible to stop your car.

[Boom n Zoom]

Alexlind,

There is nothing to really worry about, it is a pad stain from sitting in one place after it has been wet.

It is normal as the discs are cast iron they will do this all the time. My bike's Full Floating front discs always have marks from the pads on them from the humidity.

http://www.bimmer.info/forum/vbpgimage.php?do=full&p=242

See the Image for the same marks on the Bikes discs.

The don't make and shuddering but then when I do use these brakes it is pretty hard, the fact that they are fully floating rotors would also negate any slight variations in the discs (to a point)

Don't worry about how the discs look, you really can 'read into a disc' anything you want in the manner of problems. :)
Carry out BillionPA'a re-bedding proceedure then repost.

Hope this helps ya! :)

[Alexlind123]

Alexlind,

There is nothing to really worry about, it is a pad stain from sitting in one place after it has been wet.

It is normal as the discs are cast iron they will do this all the time. My bike's Full Floating front discs always have marks from the pads on them from the humidity.

http://www.bimmer.info/forum/vbpgimage.php?do=full&p=242

See the Image for the same marks on the Bikes discs.

The don't make and shuddering but then when I do use these brakes it is pretty hard, the fact that they are fully floating rotors would also negate any slight variations in the discs (to a point)

Don't worry about how the discs look, you really can 'read into a disc' anything you want in the manner of problems. :)
Carry out BillionPA'a re-bedding proceedure then repost.

Hope this helps ya! :)

Just this part, or the oven as well?:

step 1: 60mph-30mph medium pressure, 10 sets, this will remove the uneven pad material from the rotor without letting it get too hot and baking it in there, while still getting the rotors hot.

step 2: 70-20 heavy pressure, 8 sets, this should induce some brake fade after about 6 sets. if you dont get brake fade thats ok.

step 3: get up to 70, then apply light brake pressure while maintaining that speed for about 60s, then no brakes and staying at that speed for another 60s.

step 4: 60-30, medium pressure, 5 sets

step 5: 70-20, heavy pressure, 4 sets

step 6: repeat step 3, but go for 2 more mins with no brakes at about 40mph to get the rotor temp down to normal operating temp

[Boom n Zoom]

Just this part, or the oven as well?:

step 1: 60mph-30mph medium pressure, 10 sets, this will remove the uneven pad material from the rotor without letting it get too hot and baking it in there, while still getting the rotors hot.

step 2: 70-20 heavy pressure, 8 sets, this should induce some brake fade after about 6 sets. if you dont get brake fade thats ok.

step 3: get up to 70, then apply light brake pressure while maintaining that speed for about 60s, then no brakes and staying at that speed for another 60s.

step 4: 60-30, medium pressure, 5 sets

step 5: 70-20, heavy pressure, 4 sets

step 6: repeat step 3, but go for 2 more mins with no brakes at about 40mph to get the rotor temp down to normal operating temp

Sorry Alex, I skipped over the freshly baked pads :D

Yes carry out these steps and see how it feels. You will find that once the glaze has been worn through you will get significant braking force as the rotors and pads reach their full operating temperatures.

Good luck, and be safe doing this.

[Alexlind123]

Sorry Alex, I skipped over the freshly baked pads :D

Yes carry out these steps and see how it feels. You will find that once the glaze has been worn through you will get significant braking force as the rotors and pads reach their full operating temperatures.

Good luck, and be safe doing this.

Thanks, i will wait for a dry day :)