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6 Series
The BMW 6 Series builds on BMW's sporty heritage with aggressive lines and an incredible motor to back the design up. Available in coupe and convertible trims with a standard 4.8 liter engine producing 360 horsepower and 360 lb-ft of torque, the 6-series is a popular choice that exceeds expectations.

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  #1  
Old 06-26-2014, 04:37 PM
6cab 6cab is offline
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Ridges in rotor

On my left rear rotor I have ridges / grooves .


I took the car in to the dealer and they said it looked like a rock etc. got into the pads. WHen you think about it it does not make sense does it?

They decided that the pads are not uniform and this "can happen". So they are suggesting that there is pad surface missing which allowed the ridges to form from braking. They said it is not abnormal and no harm done, had fixed the trim on the convertible mechanism, washed my car, goodbye.

Then I felt a little shimmy when coming to a complete stop in certain conditions. I brought it back to the dealership the next weekend and they could not replicate the shimmy. Goodbye again.

Now I still feel the shimmy (not every time - I just notice it on smooth roads when coming to a complete stop).

Now I think that what is happening is this: the computers measure braking force on each wheel and are compensating, or attempting to, for the fact that one rear wheel has a rotor that is smooth as glass, and the other has these ridges. More braking on the right rear wheel than the left, so it is constantly adjusting.

I am afraid this will lead to other problems and possibly even be unsafe in certain conditions. Therefore the rotor should be replaced. Or ground.

What do you think?

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Last edited by 6cab; 06-26-2014 at 05:08 PM.
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  #2  
Old 06-26-2014, 04:52 PM
HerbP HerbP is offline
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If you have ridges in the rotor, they should be replaced. BMW will not turn their rotors, due to liability & want more of your money. With the grooves, they might be out of balance? At certain speeds, it would be more noticeable. I would suggest to either live with it, or replace the rotors. Yorgi has a DIY in that section, that provides a bunch of good info.

Good Luck!
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  #3  
Old 06-26-2014, 05:12 PM
6cab 6cab is offline
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You say "they should be replaced". You mean the dealer should replace the rotor since this is a 4 month old car, right?
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Old 06-26-2014, 06:44 PM
sentrex sentrex is offline
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wow 4 months i would definitely go to the dealer,but i have had this happen on some of my cars also sand pebble maybe i lived with it till i had to redo brakes
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  #5  
Old 06-26-2014, 09:28 PM
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coug60 coug60 is offline
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All rotors will have ridges and/or lines in them after use. Its due to a variety of things like trash from the road getting in, imperfections, uneven wear. They are nothing to worry about unless there are deep.

The reason you might feel a shimmy could be several things like air in the brake lines, stuck caliper piston, warped rotors or if you have over heated your rotors you can glaze them over.

A lot of car manufactures by order of congress to improve mpg aggressively started dropping a lot of weight from there cars. One of the many things they did was to take it from the rotors. Rotors use to last a long time and could usually be turned once or twice before they have to be replaced. Not the case any more. Now there good for one time only and then its time for them to go.

I don't know what your problem is or if you have a problem actually at all but the only way for you to know for sure since you said your brakes are acting funny is to start from a known state and that would be after a complete brake job. New rotors and new pads and properly bleeded of air brake lines, topped off fluid etc. Then see what your indications are.
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Last edited by coug60; 06-26-2014 at 09:35 PM.
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  #6  
Old 06-27-2014, 12:30 AM
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645/333 645/333 is offline
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I have had rotors go like that on many different cars including my 6. Even more so on my Mercedes which has drilled rotors. It can be as much to do as the material manufacture of the pads. On one set of rotors it was there, then when I changed the pads as they had run down to min, when the new pads went in they eventually took out the ridges as they bedded in over a few thousand miles. Remember that to change the profile face of those rotors takes thousand of miles, not just a quick trip down the road......Personally I would not worry, when you eventually have to change everything due to wear, then it will all change....... as for the shimmy. perhaps you are suffering from "mind over I have seen grooves on the rotor and I think it must be a major problem syndrome"! However having said this I do appreciate your concerns, but it is also part of the learning curve!!!!
I endorse the life of rotors comment, I now use two sets of pads to one set of rotors as a change policy including the rears, as on modern brake systems the rears are as active as the fronts in braking the car!!! Traction control etc. Oh by the way you are correct the wear profile can change between nearside and offside wheels especially the rears due to traction control, which side of the road you drive on and how fast you drive into corners. So one lesson is do not trust the wear sensor as they are only on two wheels front and rear offset, so the wheel without the sensor can actually wear faster than the wheel with sensor and if left unchecked (eyeball) you can damage a rotor prematurely without meaning to!!!!!!!
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Last edited by 645/333; 06-27-2014 at 12:42 AM.
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  #7  
Old 06-27-2014, 09:51 AM
6cab 6cab is offline
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Thanks for the input guys.

At this point I do have feedback from the dealer that the grooves are caused by the material manufacture of the pads - which is currently considered to be a normal inconsistency on that pad. Thus, grooves in the rotor are normal. Also some sand could have gotten in there, etc. But that is the point we are at.

The dealer has called me back after my second visit, now that the shop forman is back from vacation. So they want to look into it in more detail. I will have a loaner so they can spend the time looking into the situation.

The shimmy I feel is intermittent, at least I am not sure how to reproduce it on command. I tried to demonstrate it to a service rep driving with me.

But it does have a rythmic shimmy as I apply the brakes sometimes when on a very smooth or newly asphaulted road, when I come to a complete stop. I feel this sitting in my seat, not in the steering wheel.
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2014 650i Cabrio (current) M Sport package and edition Carbon Black : Black Nappa leather dashboard:Active Driving Assistance:Lane Departure Warning:Active Blind Spot Detection:Side and Top View Cameras:Speed Limit Info (sometimes ignored)
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Last edited by 6cab; 06-27-2014 at 01:18 PM.
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  #8  
Old 06-27-2014, 08:20 PM
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Yorgi Yorgi is offline
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I have never seen gouges that deep in a rotor, especially after only 4 months of use. I would guess the gouges are the sole cause of the braking vibrations and are due to a bad brake pad.

I have seen gouges caused by 2 things:
1) stones or metal debris becoming embedded into the pad which typically causes 1 or 2 small gouge rings in the rotor.
2) impure / non-uniform pad material caused during manufacture of the pads. I've seen chunks of harder resin or metal "floating" in with the rest of the brake pad friction material which can cause groves to be cut into the rotor.

After removing and inspecting the pads the dealer would likely know the cause. I don't think these gouges are a safety issue but they are an annoyance, especially on a new ultra-premium car. If it were me I'd go back and insist they replace the bad rotor and install a set of new pads on both rear axles - there is an obvious defect going on here and if the grooves get any deeper they will be a serious safety issue.

[edit]If the dealer pushes back tell them to measure the rotor thickness at the bottom of the groove, you are probably very very close to minimum safe rotor thickness and if this uneven wear continues the thickness at the bottom of the grooves will soon be unsafe (below min rotor thickness). Since the pad is causing the grooves, these need to be replaced and you must change BOTH sides of the pads at the same time.
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Last edited by Yorgi; 06-27-2014 at 08:31 PM.
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