rotor must be centered in caliper carrier, right? what went wrong?

As a guess, they put the wrong rotor on it. I'd dig up some specs and take some measurements.

By the photos, it looks like the caliper is hanging up on that flange behind the rotor and not letting the caliper float. Also appears that something (brake pad?) is rubbing the rotor hub. Will the caliper slide outward off the flange? Does the caliper float on the sliders?

that rotor is never going to look centred because the caliper bracket is "floating" the rubber covered studs that it bolts to should allow the bracket to push back towards the rotor face some. They often seize up, so make sure it moves easily against the spring pressure that is pushing it the way it is at the moment.

I am not sure the rotor needs to be centered in the caliper carrier.

The caliper needs to self-center on the rotor. It's possible that may not have a correlation to the carrier.

If the caliper was sticking and not self-centering, the piston could have pushed a pad out (though that usually happens when the pads are shot beyond shot).

Are you sure you re-installed the pads correctly? Seems fishy that the pad dropped out right after you took it apart and reassembled it.

Were the pads worn equally? If the caliper was sticking, one pad should wear much more than the other.

I think you've got the wrong rotors on that car.

The brake pads stayed in the carrier while they were new, but 50% wear was enough to drop the rotor on the side with more clearance.

I don't see how it's the bearing.

I'll bet the vented rotors you referred to were thicker overall, and centered differently on the carrier.

Check the specs, then buy a pair of correct rotors.

looks like you got 2 door solid rotors on a 4 door that calls for vented ones. someone before you boned up, and the pads wore enough to fall out with the thinner rotor.

Looks like the 4 door car should have vented rotors like this:

The 2 door car has solid rotors like this:

See the difference in overall thickness?

You've got the wrong rotors.

In reply to iadr:

OK.

Don't get defensive. Read on- it ain't your fault.

But you DO need to replace the rotors. Right away.

And don't play that shim game. That's an accident waiting to happen.

In reply to iadr:

Don't need photos. Thanks for the show!

You've given enough info already. This case is closed.

I'll just leave this here.

Toyman01 wrote: As a guess, they put the wrong rotor on it. I'd dig up some specs and take some measurements.

Glad you figured it out before something major happened. That could have ended rather poorly.

I'm jealous. I've been keeping an eye out for one for a while. They are holding their value surprisingly well.

Does it use press in bearings or bolt on hub units?

I suspect the different brakes came with different hub units, you had solid brake bearings and rotors, you had new hub units installed that were for the vented brakes. That or if it has press in bearings, the shop screwed up royally and pressed it together wrong.

In reply to Kenny_McCormic:

I think you misread.

It came from the factory with vented rotors.

OP installed the hubs, but the rotors were done by the previous owner.

In reply to SVreX:

Right, and we don't know what hubs the PO had on it.

Kenny_McCormic wrote: In reply to SVreX: Right, and we don't know what hubs the PO had on it.

Still don't understand.

Why does it matter what hubs the PO had? They're gone.

I don't see anything here that indicates anything wrong with the hubs at all.

I think it is reasonable to assume that the import shop that just installed the hubs installed the proper ones, until some evidence shows otherwise.

The rotors are wrong. Until that is fixed, nothing else can be determined.

I'm hypothesizing it had the wrong hubs on it and rotors to match, correct hubs are now fitted, and that's why the (incorrect) rotors no longer match.

In reply to Kenny_McCormic:

I think you are trying to solve a problem that does not exist.

Some dipE36 M3 bought the wrong rotors. The caliper bracket is the right one for the car- for vented rotors. Pads worked OK until they wore enough to fall through the gap.

I doubt the hubs have been replaced twice, and dipE36 M3 who didn't know how to buy rotors certainly didn't know how to install a hub.

Get to the suspension swap- talk already!!!!!