3.3TT Abnormal Rotor Wear

[Unconventional]

Long time lurker, first time poster.

Please me help identify my issue. I'm fairly savvy with cars but this escapes me. For context, US military stationed overseas. Relevant for driving/braking conditions explained below.

2020 Kia Stinger, 3.3L TT, AWD. Euro Spec. Pads and Rotors linked below.

I installed myself under supervision of master mechanics with proper equipment. Conduct proper break-in and bedding of pads and rotors according to manufacturer guidelines. Drove extremely cautiously for first 200km post-change per manufacturer instructions as well.

I replaced the rotors and pads, front and back, about 2000 km/ 1200 mi ago. Brakes stop well but feel "squishy" and as if their not "grabbing" as much as they should under heavier braking. Staying on the brakes for an extended period of time (sometimes necessary when driving in Germany on the Autobahn) produces vibration and causes the brakes to produce noise until I let off of pedal. I also hear a very slight "clunk", as if the pads are clapping against the rotors when initial depressing brake pedal at low speeds... sometimes.

Looked at rotors today and noticed weird pattern/discoloration (photos below) on both sides. Only on the fronts. Rear look normal. When I run my figure over the discoloration, it feels completely smooth on all axes. No bumps, hills, valleys, gouges.

I am vexed. Any ideas/recommendations/fixes/etc. are most welcomed! Thanks.

Pictures of rotors, along with link to which pads and rotors were used are on Reddit as I can't post links or pictures. u/ohreoman85 in subreddit r/mechanicadvice under title Abnormal Rotor Wear.

Pads -

DBA DB15003XP - Brake pads Xtreme Performance ECE R90 certified | Front axle (and compatible rears)​

Rotors -

BREMBO BRAKE DISCS 350mm INTERNALLY VENTILATED FRONT (and compatible rears)​

• Brake disc type: Internally ventilated
• Brake disc thickness [mm]: 30
• Number of holes: 5
• with screws
• Height [mm]: 57
• Centering diameter [mm]: 69
• Outside diameter [mm]: 350
• Processing: high carbon
• Surface: coated
• Minimum thickness [mm]: 28
• Additional designation: PRIME LINE - UV Coated

 

[ElChanclo]

[Link to reddit post]

I have the same Brembo (not KIA) rotors, and they're doing great.

What bedding procedure did you follow? I suspect it's the pads leaving that spotty deposit but not familiar with the brand.

 

[D.J.]

I also hear a very slight "clunk", as if the pads are clapping against the rotors when initial depressing brake pedal at low speeds... sometimes.

Those DBA pad specs seem to indicate that they are undersized a bit, which may result in the "clunk" you are hearing!



I measured the OEM Brembo front pads years ago



And most online resources say either 132mm or 131.8

 

[Snicklefritz]

Staying on the brakes for an extended period of time (sometimes necessary when driving in Germany on the Autobahn)

Are you saying that at autobahn speeds you sometimes have to come down to a complete stop and hold the brakes? Those spots look like heat spotting to me, where the rotor got really hot and then the car was held stopped for a long moment. If those are cementite spots then your rotors are literally cooked, resurfacing isn't possible.

If you are heating up the rotors with heavy braking at autobahn speeds, but continuing to roll, there won't be any cementite and the spots are something else entirely, I have no idea what.

 

[D.J.]

If those are cementite spots then your rotors are literally cooked, resurfacing isn't possible.

Why?

It may not be recommended, but I did it!

 

[Snicklefritz]

Why?

It may not be recommended, but I did it!

I have read that cementite attracts pad deposits, thus producing the shuddering brakes problem. And cementite cannot be ground off because it penetrates the depth of the rotor. You must not have had cementite if resurfacing fixed your rotors.

 

[Mapleton 21]

Check your rotors are not warped I went through 2 sets bad batch.