FYI - Zimmerman Rotors

[cobra]

I wanted to share some insight on my recent experience with Zimmerman rotors. I bought these because I needed new rotors and they have a good reputation. They have a zinc coating that is supposed to prevent corrosion.

I noticed, however, that the zinc coating can "squeeze" out of the clamping areas - either between the rotor and hub, or the wheel and rotor, and therefore reduce the clamp load.

-The first time I was having pulsing issues during braking, I found a large amount of flaky zinc material between the hub and rotor.
-The second time, after a track day, I noticed the same type of debris flaking off between the wheel and rotor.

In both cases, the torque on the lug nuts felt about 20% lower by feel than what I consider normal. They were installed at 90ft-lbs as I always do.

After removal, clean up, and reinstallation, everything is fine.


TLDR: If you have Zimmerman rotors, I recommend re-torquing them frequently until the mating surfaces wear in. Alternatively, remove the zinc coating from the mating surface before installation (it can wipe off with solvent & rag). Or, just go with OEM and save the headache.

Has anyone else run into this?

[Slideways]

I have seen it where the rear wheels need to be torqued again after coming back from a test drive after performing wheel-off work - wheels mounted, torque down to spec, test drive, torque wheels again after test drive

OE BMW rotors come with the hub mounting surfaces bare metal FWIW.

[Estoril]

I use Zimmerman blanks on the rear of my track-only M3 and have never observed those problems. I watch rotors very closely after every session and cold torque-check every morning and after lunch with zero drift (using studs). No braking feel issues either and I'm pushing brakes at the limit. Maybe your pad selection affects the 'flake' observation you've had (I run PFC-11 front and rear).

[01SG]

I removed the coating before installation with these and have had no problem.

[cobra]

I use Zimmerman blanks on the rear of my track-only M3 and have never observed those problems. I watch rotors very closely after every session and cold torque-check every morning and after lunch with zero drift (using studs). No braking feel issues either and I'm pushing brakes at the limit. Maybe your pad selection affects the 'flake' observation you've had (I run PFC-11 front and rear).

FWIW I noticed this issue primarily on the front rotors. The zinc coating appears very thick. I was running stock pads, so no crazy braking forces or anything.

I wish I would have taken a picture, but picture a paper-thin curled up silver material around the mounting surfaces that is brittle when touched.

[OldRanger]

For sure - remove the coating. Same experience here; it was alarming.

Acknowledging Estoril - there may be differences from one batch of rotors to another. A drill-powered wire brush takes it off rapidly. Wear a mask (cough).

[jayjaya29]

Core4 has documented this issue:

https://www.core4motorsports.com/coa...l-stud-failure

TLDR: "In the case of Zimmerman rotors, this effect will be worst when they are brand new during the first few track sessions. This is why we highly recommend to just remove the coating on both sides of the rotor when they are new with a wire brush wheel or similar to remove any variable that facilitates any loss of preload."

[cobra]

Core4 has documented this issue:

https://www.core4motorsports.com/coa...l-stud-failure

TLDR: "In the case of Zimmerman rotors, this effect will be worst when they are brand new during the first few track sessions. This is why we highly recommend to just remove the coating on both sides of the rotor when they are new with a wire brush wheel or similar to remove any variable that facilitates any loss of preload."

Wow, wish I would have seen that earlier. Exactly what I have experienced.

[BlueBimmers]

Interesting. Haven't experienced but also haven't tracked car. Personally I hate how OEM rotors rust over, like the Zimmerman coating. Guess I'll check the lug torque more frequently.

[Nate047]

Interesting, so if you remove the coating on the rotor around the area where the wheel studs go, that area will be bare metal and get rusty and shitty looking, but it will be mostly hidden by the wheel, soooo because racecar

[cobra]

Interesting, so if you remove the coating on the rotor around the area where the wheel studs go, that area will be bare metal and get rusty and shitty looking, but it will be mostly hidden by the wheel, soooo because racecar

I think you can still put a thin layer of antiseize on the surfaces to help with corrosion and it will just get squeezed out immediately.