I've got a pair of cryo'd powerslots which were installed on the front about a year ago, and have occasionally heard a grating noise once the brakes get hot. Finally pulled all four wheels today... no dragging slide pins, plenty of pad inside and out, but the driver side front cryo rotor has polished ridges on both faces. The other front cryo'd rotor is perfectly smooth.

I'm thinking manufacturing issue with the rotor since the ridging is on both inner and outer faces, and not on the other rotor at all. I would not expect it to be the Hawk pads because they were installed new with the rotors on both fronts, and it would be rare for two pads to have the exact same ridged wear pattern inside and out.

What say you guys? Any thoughts?

Picture coming later. Having trouble getting it off my phone right now.

UPDATED 07/14/2015... look at post #22

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Ridges on the shiny part of the rotor or on the outside edge where the shiny part has worn down some?

Guess I'll wait on the pics.

 

On the face where the pads make contact. Not the edges.

 

Pics of the pads?

 

Looks like pads to me. Had some cheap autoeroticazone ceramics on the wife's Subie do that, grinding sound when hot included. They had largish chunks of a reddish material in the pads, picked them out and problem went away. Until pads wore down enough to expose more reddish chunks.

Swap pads DS to PS, see if problem follows. Should see evidence in a couple hundred miles I 'spose.

Metallurgically I can't see how the casting process could make concentric hardness variations like that. Does the inside ridge pattern mirror the outside?

 

After my experience with slotted rotors, I vote debris in a slot at one point. I could be wrong.

 

I did not pull the pads & calipers. Just did not have the energy at that point in my day, but will do so one evening this week. Not doing it today because my older kids are coming over for Father's Day, and spending time with them matters more right now because I can do without the truck for another couple of days if I have to.

OK... to respond to all the input thus far. First... thank you for your thoughts and ideas. I like being stretched by them.

Pads... these are not cheapies... they are Hawk LTS pads which were installed brand new with the brand new cryo'd rotors, and were properly bedded upon install... new caliper slide pins went in at the same time and were properly (lightly) lubed with the Permatex ceramic brake lubricant. Regardless, I understand that it could be pad material contamination and will check for that specifically.

Inner versus outer... since I did not remove the rotor, I cannot say that the pattern is exactly identical, but I CAN feel the ridges on the inner disc surface., and they seem to be in a similar pattern with similar height. Whatever happened happened on both sides of the rotor at about the same time.

Although I understand the metal forming process and how each disc plate (inner and outer) on the same rotor are different and may not come have from the same sheet blank. They are, however, bonded together and built together in a single process, and it is that specific construction process of building the rotor assembly which becomes potentially suspicious in my own mind. Ultimately, I see it more likely that the disc building process could go wrong as opposed to having two individual pads BOTH go wrong at the same time ... unless they were in a "bad" batch together, and I guess that could happen as well. I simply see the "two pad" problem almost being more of a double failure issue than that of the rotor construction process. I may be wrong.

MORE observations, though... this particular DS rotor has more short term "rust spots" than any of the other three rotors on the truck, and to me, this helps lean my suspicions more towards the rotor being the villain in this mystery. The ridges are also nearly equally spaced. Furthermore, I am now beginning to wonder if i might have received one rotor which did not get cryo'd because there is much more wear on this rotor as compared to the PS rotor, and the ridges might be from the welding-sourced thermal stresses for the studs between the disc plates. Hmmm... I'm going to go ahead and contact Frozen Rotors and present this as a point of concern to see how they respond.

Contamination in a slot... Interesting thought, Rich. I will certainly check specifically for that when I pull the rotor. I still find it sort of unlikely that both sides of the rotor would have received similar slot contamination at the same time... again, the ridges on both sides feel equally tall.

Swap pads from side to side (or rotors). Although I clearly understand and support the principle behind this approach to troubleshooting, it is not always the best thing to do. The reason I won't do that in this case is because i am currently getting 100% surface contact on both sides of both front rotors. If I swap, there is a significant chance of one or more of several bad things happening...

1) damaging a perfectly good set of pads from the PS side of the truck by forcing them to run on the ridged disc rotor,
2) damaging a perfectly good PS rotor if the problem is bad (contaminated) brake pads, and
3) decreased stopping potential on both sides of the truck (less contact on the PS by using "grooved" pads and only "groove top" contact on the DS with flat pads. I'm simply not up for that kind of risk. The only way I would consider swapping pads is if I had the DS rotor resurfaced to get it flat again, and I might have to do that if I find the pads to be the villain, but not until I know that is the true culprit.

Keep in mind, guys, that if it is the pads, the issue has to be coming from hardened, elongated contaminants as opposed to small chunks of stuff. The ridges are further apart than the worn "flats" between the ridges. If it were hardened chunks of contamination, I would be wearing grooves in the rotor surface, not leaving ridges. Again, this is also part of why I lean towards a rotor manufacturing process issue as opposed to a pad manufacturing issue.

I'll keep you posted as I learn more, and will take more comparative pictures as I dig deeper.

 

Some good reasoning there Pete, leans me toward rotors too.

The contaminants in the pads I had were of various irregular sizes, from tiny bits I did not address up to 1/4 inch. Looked like bits of brick.

The rotors are cast metal, not stamped from sheet or ingot. Molten iron is poured into a mold so the result is one contiguous part. If that pour is briefly interrupted then continues, the leading edge of the flow in the mold can begin to solidify. Iron will change phase and carbon will aggregate there, and that crap is hard. Once the flow continues there will be a boundary layer. That said, the onion-like muItiple layers would require a ton of interruptions.

Maybe the surface is induction hardened, and the machine was on the fritz and missed sections like a skipping record. All the other heat treat and cryo should affect the piece as a whole since they are environmental changes in temp. Opinion of rotor manufacturer would be good.

This may be a case of my little knowledge being worse than no knowledge at all.

 

Good input, David. Thanks. What I know of metals is from my Materials class in college (31 years ago) combined with my engineering work in industrial complexes for the last 30 years. That said, it is in no way what I would call DEEP knowledge, and you are obviously more in tune with the technical details than I.

 

I've never seen any that bad. I would make sure the calipers are not locking up. The rust maybe from salt or excessive moisture.

 

No salt (I'm in Birmingham, AL). No excessive moisture (the truck had been sitting for a full 7 days without being driven when I pulled the front wheels to check the brakes). The other rotors all looked clean in comparison... there is simply something different about this particular wheel's rotor (or pads, or both).

Also, the calipers are not locking up. The wheels spin freely.

 

Called manufacturer and left message this morning. Called again a few minutes ago and spoke with a technician who requested that I send pictures. The document package (invoice, shipping notice, and picture of damaged rotor) is now in their inbox. Hope to hear back very soon. Will post findings and progress.

 

I would turn the rotors and put the pads on a good flat belt sander to flatten them out and reinstall, it might sound crazy but I bet you won't even notice a differance, besides, you have nothing to lose!
I have tried cryo rotors and hawk pads three different times with less than exceptable results on my trucks in sig, never again will I spend that kind of money on brakes, back to OEM Ford rotors, pads.....

JMO

 

Waiting to here what they say. I've seen other trucks with cryo'd do the same thing. Don't know what brand they were but they weren't happy either. If done right it shouldn't happen.

 

How are your wheel bearings?

These rotors are a floating design and if the wheel bearing is out it will have some wobble motion. Mine has a scratched line the circumference of the rotor from when the wheel bearing was spun.