[R608]

Can anyone point me to a spec that says what the acceptable runout is on the front brake rotors (OEM) for a 325i/328i? I replaced my front pads and rotors recently and am periodically noticing a slight pulsation as I'm slowing. Driver's side rotor rotates smoothly and evenly by hand. The passenger's side one sticks in one area, though, and my dial indicator is showing roughly 3.5 thousandths of an inch variation (measured within 1/2" of the edge) as I turn the rotor by hand.

http://workshop-manuals.com/bmw/3_se...ont_brake_e90/

It should also be stamped on the rotor itself.

[R608]

Thanks, but both appear to reference thickness rather than runout.

[john16443]

Not that it is BMW specific, but during my rotor research, I noticed that the NAPA ultra premium rotors had a runout of 0.002", while the NAPA premium rotors had a runout at 0.004". These were for my 335i rotors.

What you might be experiencing is pad material that has been deposited on the rotor, causing what is sometimes described as brake judder, pulsations, or thinking you have a warped rotor. Try to do a brake pad bedding cycle before you do anything else. Perform at least a half dozen moderate to VERY firm (not full panic) stops from 60 to about 10 mph, consecutively. Never come to a full stop during this process. Basically get up to 60 quickly, down to 10 quickly, and back up to 60, repeat 6 times. After this, run at normal speeds for at least 10 minutes to let the brakes cool and try not to stop at all until they are fully cooled. You will have them removed any old pad material from the rotor and deposited a nice even layer of new material. You may notice that your brake system operates better than it did before.

[drunkenup]

Originally Posted by john16443

Not that it is BMW specific, but during my rotor research, I noticed that the NAPA ultra premium rotors had a runout of 0.002", while the NAPA premium rotors had a runout at 0.004". These were for my 335i rotors.

What you might be experiencing is pad material that has been deposited on the rotor, causing what is sometimes described as brake judder, pulsations, or thinking you have a warped rotor. Try to do a brake pad bedding cycle before you do anything else. Perform at least a half dozen moderate to VERY firm (not full panic) stops from 60 to about 10 mph, consecutively. Never come to a full stop during this process. Basically get up to 60 quickly, down to 10 quickly, and back up to 60, repeat 6 times. After this, run at normal speeds for at least 10 minutes to let the brakes cool and try not to stop at all until they are fully cooled. You will have them removed any old pad material from the rotor and deposited a nice even layer of new material. You may notice that your brake system operates better than it did before.

I've been having symptoms of increased runout on my rotors (I can feel the high spot so badly I can't come to a standstill smoothly because the braking force varies so much at crawl speed). I tried this twice to no improvement, perhaps I actually have what people say does not happen anymore. I've only been using these rotors for about 9 months and 4000 mi, dealer installed, BMW OEM parts.

[R608]

Originally Posted by john16443

Not that it is BMW specific, but during my rotor research, I noticed that the NAPA ultra premium rotors had a runout of 0.002", while the NAPA premium rotors had a runout at 0.004". These were for my 335i rotors.

What you might be experiencing is pad material that has been deposited on the rotor, causing what is sometimes described as brake judder, pulsations, or thinking you have a warped rotor. Try to do a brake pad bedding cycle before you do anything else. Perform at least a half dozen moderate to VERY firm (not full panic) stops from 60 to about 10 mph, consecutively. Never come to a full stop during this process. Basically get up to 60 quickly, down to 10 quickly, and back up to 60, repeat 6 times. After this, run at normal speeds for at least 10 minutes to let the brakes cool and try not to stop at all until they are fully cooled. You will have them removed any old pad material from the rotor and deposited a nice even layer of new material. You may notice that your brake system operates better than it did before.

Thanks for the response. I gave the bedding process another go this morning, this time doing more cycles and starting out a bit easier, then gradually getting more aggressive. They were feeling better by the end, though it's looking like I've picked up a more persistent squeal (there was a mild one that I heard occasionally before). I'll just have to see how they do over the next couple of days of normal use and go from there.