Rotor Groove and Pulsing/Vibration

[SlickShift]

I had the front right wheel off the car the other day (to replace a turn signal bulb) and realized the rotor had a noticeable groove in it about an inch from the outer circumference.

I've been getting intermittent pulsing/vibration under moderate braking. I checked rotor thickness and the pads on all corners and everything was within spec. Not sure if the groove could be causing the pulsing/vibration or if there could be another culprit.

[Finnegan]

Pic?

Vibration is probably due to uneven pad deposits. Re-bed brakes see if that helps.

[inTgr8r]

^whs
Most rotors develop grooves as they wear and shouldn't cause vibrations

[SlickShift]

Here's a shot of the groove.

[inTgr8r]

That's generally considered normal wear.
If it concerns you, you can pull the pad and see if there's a hard spot or something trapped on the pad

[SlickShift]

Ok, thanks. I'll have to check the pads.

[The HACK]

How many miles on the car?

[Finnegan]

Originally Posted by The HACK

How many miles on the car?

Are you thinking worn bushings, etc.?

[SlickShift]

81K miles on the car.

[inTgr8r]

Original rotors?

[The HACK]

Originally Posted by Finnegan

Are you thinking worn bushings, etc.?

Possibly. High mileage/worn FCAB can sometimes have similar symptoms. Inconsistent brake shudder at speed. Because on first sight the rotor appears to be in decent condition.

[SlickShift]

Originally Posted by inTgr8r

Original rotors?

Yeah, original rotors as far as I know. Bought the car with 64K on it and I haven't changed them.

Thickness checked out fine on the digital calipers though.

Originally Posted by The HACK

Possibly. High mileage/worn FCAB can sometimes have similar symptoms. Inconsistent brake shudder at speed. Because on first sight the rotor appears to be in decent condition.

Any other symptoms of control arm bushing wear? Everything still feels pretty tight.

[The HACK]

Originally Posted by SlickShift

Any other symptoms of control arm bushing wear? Everything still feels pretty tight.

First thing to look for is any sort of cracks in the FCAB itself. Stuff might look tight, stuff might FEEL tight, but most of the modern age BMW FCABs are fluid filled. If they cracked and the fluid leaked out, then for all intent and purposes they may look okay and feel okay, but they're toast.

If you can jack the front end up in the air, you can try and hit the control arm by the bushing with a heavy mallet and see if the bushing deflects. Bushings that are worn but have not leaked yet, will allow for some level of deflection when you hit the control arm hard with a mallet.

Lastly...At 81K mile, they're about due for replacement ANYWAY. The shudder you feel in the brakes are from the control arm moving inside the bushing, transferring the movement into the steering knuckle into the steering rack and wheel.

If you have a new set of rotors, new set of pads, and they're vibrating while braking at certain speeds, then I would suspect the FCABs require a replacement. Since you don't really know the age and usage on the rotor, then at this point it's a crapshoot. I'd replace the FCABs due to age regardless of whether or not that solves your brake issues. IMO.

[SlickShift]

Made an observation after washing the car today. I took the car for a drive to the end of the street and back to get the rust off the rotors and noticed the driver's side rotor wasn't cleaned while all the others were. It looks like the pad was only coming in contact with the inner diameter of the rotor. It's felt like the grinding/groaning/pulsing was coming from the driver's side (coincidence?). Chances it could just be the pads, or do I need to suck it up and buy new rotors too (even though they're in spec)?

Surface rust still on driver's side rotor



Passenger ride rotor for comparison

[dc_wright]

Originally Posted by SlickShift

Made an observation after washing the car today. I took the car for a drive to the end of the street and back to get the rust off the rotors and noticed the driver's side rotor wasn't cleaned while all the others were. It looks like the pad was only coming in contact with the inner diameter of the rotor. It's felt like the grinding/groaning/pulsing was coming from the driver's side (coincidence?). Chances it could just be the pads, or do I need to suck it up and buy new rotors too (even though they're in spec)?

Surface rust still on driver's side rotor



Passenger ride rotor for comparison

What you're seeing there is typically a symptom of the caliper not free floating on the guide pins. If everything's correct the caliper should be able to move laterally on the guide pins, center itself on the rotor, and apply equal pressure to both sides of the rotor. You need to pull that caliper and check the guide pins. They're inexpensive enough I'd just replace them.
If that caliper is frozen in place or not moving freely that will give you a vibration under braking, and potentially also while underway since the caliper can't freely move away from the rotor surface.

[SlickShift]

Originally Posted by dc_wright

What you're seeing there is typically a symptom of the caliper not free floating on the guide pins. If everything's correct the caliper should be able to move laterally on the guide pins, center itself on the rotor, and apply equal pressure to both sides of the rotor. You need to pull that caliper and check the guide pins. They're inexpensive enough I'd just replace them.
If that caliper is frozen in place or not moving freely that will give you a vibration under braking, and potentially also while underway since the caliper can't freely move away from the rotor surface.

Thanks for the info. I'll pull the caliper and check things out.