new brake rotor

[BladeRider]

Hello!

I've purchased two new rear brake rotors. They are original Volvo. One of them has a milling on the side, which I thought and the store confirmed, that it is from balancing. What seems weird to me is that the milling is as wide as the rotor.
Did anyone see something similar? Thank you!

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[jimmy57]

The pad contact on older platforms not across the face to the edge. There is 2-3 mm of non contact area. On models where this is true the metal can be removed on full edge as with yours. On the models where the contact is within a narrow margin of edge due to not having the extra weight the margin introduces, the balance cuts are deeper down into the vent region and leave 3mm or more behind the surfaces.

[BladeRider]

... the balance cuts are deeper down into the vent region and leave 3mm or more behind the surfaces.

Thanks. There is no vent region on these rear rotors on my car. Only in the front rotors. I've seen the balancing milling on the front ones and it is indeed as you said. I was just uneasy about the rear one extending to the whole width (only one has a milled portion, not both).
I'm not a pro mechanic, just a DIY one and I lack the experience of seeing many parts and the way they're made.

[- Pete -]

It’s a little hard to tell from the picture, but it almost looks like it cracked off.
Can you put up a slightly clearer image?

[oragex]

I've yet to see such 'balancing' on any car at the junkyard. The question is, why would this particular rotor need balanced ? These are all cast then machined with the same parameters, why would one become unbalanced ?

[BladeRider]

It’s a little hard to tell from the picture, but it almost looks like it cracked off.
Can you put up a slightly clearer image?

Clearly machined, not cracked. And very little. Brand new, got it sealed with Volvo stamping on it and labels on the box.

[BladeRider]

I've yet to see such 'balancing' on any car at the junkyard. The question is, why would this particular rotor need balanced ? These are all cast then machined with the same parameters, why would one become unbalanced ?

Many rotors come with a milled out notch like this:
https://www.powerstop.com/mill-balanced ... tor-notch/

I've also got a set of Brembo rotors for the front and they are both milled like in the link above. It's just that I haven't seen it yet on a rear rotor and all the way to the lateral surface.

[oragex]

I see. Given that most rotors don't need this, I wonder if there have been some issues during the casting process. Not necessarily something to worry, but I'd say it's perhaps one of the few that weren't made 'perfect'. Maybe the melted iron didn't properly fill all areas of the mold. I would rather call this a 'reject' especially give the OEM standards.