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I had my front rotors and pads replaced for the first time this past December at about 41K miles due to car vibration when braking--per my invoice, the rotors were warped and the pads were down to the sensors (I hadn't gotten a light yet).

Now the braking shudder has returned and the dealership says the the new rotors are warped and they want to replace them--this is with about 5K mile on them.

-Can the rotors be measured by a machine to see if they are indeed warped?
-My snow tires were checked for wear, etc to see if this could be the cause.
-Could another component of my braking system be causing the problem--ie calipers or somthing?
-Ever hear of rotors getting warped under normal driving conditions in just 5K miles? Cause(s)?
-Any other ideas?

THANKS SO MUCH!! I hate to have the rotors replaced if something more complex is going on!!!

Anita
 

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Anita said:
I had my front rotors and pads replaced for the first time this past December at about 41K miles due to car vibration when braking--per my invoice, the rotors were warped and the pads were down to the sensors (I hadn't gotten a light yet).

Now the braking shudder has returned and the dealership says the the new rotors are warped and they want to replace them--this is with about 5K mile on them.

-Can the rotors be measured by a machine to see if they are indeed warped?
-My snow tires were checked for wear, etc to see if this could be the cause.
-Could another component of my braking system be causing the problem--ie calipers or somthing?
-Ever hear of rotors getting warped under normal driving conditions in just 5K miles? Cause(s)?
-Any other ideas?

THANKS SO MUCH!! I hate to have the rotors replaced if something more complex is going on!!!

Anita
The rotors are not "warped." You have a pad deposition problem. Try rebedding them per the instructions here and see if the problem goes away: http://www.zeckhausen.com/bedding_in_brakes.htm

If you want to understand the physics behind what is happeneing, read the following white paper: http://www.stoptech.com/whitepapers/warped_rotors_myth.htm
 

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Anita
To follow up Dave Z, the rotors can be checked to see if they are warped. They can me "miced" (measured with a micrometer) for "runout". If the runout is over a certain spec, then they are out of round, or warped. Unlikely as Dave Z suggests, but have the service department prove they are warped by taking measurements if that is what they claim. BTW, bad thrust bushings will cause a similar shudder to warped rotors. At your mileage, I would have those checked also.
Regards,
Jerry
 

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gsfent said:
To follow up Dave Z, the rotors can be checked to see if they are warped. They can me "miced" (measured with a micrometer) for "runout". If the runout is over a certain spec, then they are out of round, or warped. Unlikely as Dave Z suggests, but have the service department prove they are warped by taking measurements if that is what they claim. BTW, bad thrust bushings will cause a similar shudder to warped rotors. At your mileage, I would have those checked also.
Actually, a micrometer would be used to measure thickness variation by comparing rotor thickness at various points around the rotor. This measurement will probably confirm a thickness variation that exceeds 4 ten-thousandths of an inch. That's how much variation is required before you can feel it in your foot as judder under braking.

To measure runout (or "warping") you need a dial indicator. The dial indicator is solidly mounted to a suspension component with a clamp and the tip is placed against the face of the rotor, near the outside edge. The rotor is carefully rotated 360 degress while observing the deflection of the needle on the dial indicator face. If runout exceeds 6 thousandths of an inch, your rotor is "warped" or improperly mounted to the hub (probably rust trapped between rotor and hub).

As you can see, the amount of runout required to be felt in your foot is more than an order of magnitude greater than the amount of thickness variation.



Micrometer


Dial Indicator
 

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Anita

I had the same kind of problem this winter. My front left caliper seemed to lock up on me while on the highway. The car shuttered just like the rotors were bad. The dealer had both fron calipers rebuilt and the rotors ended up being fine.

You may have a bad caliper. No way should the rotors go bad after 5000 miles.

Bill
 

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Dealers don't understand this issue. They just replace the rotors. I had this problem when running stock pads and they replaced them. At the time I didn't know the real reason and didn't care because it was covered under warranty. Now I hardly get this anymore but when I do, the bedding procedure always works as a cure.

Jerry, that's "mic'd" not "miced." The latter is when you put mice into someone's car. hiha
 

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As per Dave Z., the issue is pad deposit on the rotors.

The bigger issue (and path toward the cure) is the OE pads. From Day One with the E39 M5, testers have noted that the standard-issue pads are insufficient for such a heavy car. These aren't "///M" pads, they are "///Marketing" pads and are nice and quiet, and don't upset Grandma in the consumer clinics. Bah.

Save me from the mundane and mainstream.

Performance cars use performance parts, and brakes start and end with pads (all the caliper and rotor variations in the world cannot overcome an insuffcient pad). Look to replace yours with something a bit more aggressive, that has a higher heat range than the biscuits that the dealer installs.

For a good listing of pads available for the M5, visit this page on TireRack's website:

http://tinyurl.com/52wfl

I have personally used just about all the pads listed on that page in the quest to learn exactly what the differences are in real-world situations.

For your M5, especially considering your repeated problems with pad deposits, I would recommend either the Akebono ProACT ceramic pads or Hawk ceramics. The SP GrandSport and Hawk HP+ may squeal a bit excessively for you, and the response curve is more abrupt than the aforementioned ceramic offerings. Another benefit to the ceramics is extended mileage; we've long-term tested this type of pad and the results simply blew us away... I'm talking about thousands of miles with barely any wear. The technology in modern ceramic pads has taken a big step forward in the past couple of years.
 

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hudson said:
Rob another benefit in ceramic pads is much less brake dust to keep those beautiful wheels cleaner longer.



Joe
Bingo! I knew I forgot to mention something.

"Dustless" falls way down on my list of important brake pad characteristics, and many of the popular "dustless" pads work quite poorly. Nevertheless, these particular ceramics do indeed fulfill that nearly dustless criterion quite well.

We should also emphasize "quiet"... they don't squeal at all, and make for an exceptionally smooth pedal application even when exceeding their max heat range.

- Rob
 

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I think you can get the Hawk Performance Ceramics from Zeckhausen Racing, too.
 

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Anita,

Have you taken off and re-mounted your tires/wheels since you replaced the rotors?

I had the same problem in my old M5. I could not see any hot spots on the new rotor, and spinning them shows no warpage visibly. A very experience mechanic told me that excessive torque on the lug nuts can warp the rotors causing vibrations. I bought new tires with the new rotors, so that could be the case. Of course there's no way to prove it at this point (car is totaled).

Just thought you might want to check this item out.

Good luck.

CP
 

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hudson said:
Rob
Should you bed in ceramic brake pads? I've used them on different applications but not on my M yet.
They need to be bedded, just like any other pads. Hawk includes instructions in the box.
 

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Discussion Starter #14
gsfent said:
Anita
They can me "miced" ........
Regards,
Jerry
Jerry,
They did "squeak" a lot right after they were installed--sorry I couldn't resist teasing you about that too. And BTW, I really like mice, so no bad comments about them please.

Seriously, everyone thanks for the feedback. I'm waiting to hear back from my SA and/or tech to see what measurements, if any, were taken the other day.

And, I thought I followed the DaveZ break-in plan right after I got the new pads/rotors installed, but I'll repeat it (?).

My old OEM wheels for summer go back on shortly--I could see if that makes a difference too.

I did run EBC Greens on my M5 back in spring of '03 for a short time--not that impressed. Maybe time to try a new pad?

I'm going to be out of warrany soon (don't know if I'm going the extended route or not), so I would like to get it sorted out before then!

Thanks again!!!

Anita
 

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Need4Spd said:
Jerry, that's "mic'd" not "miced." The latter is when you put mice into someone's car. hiha
No response, cat got my tongue........ :biggrin:
Regards,
Jerry
 

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DZeckhausen said:
The rotors are not "warped." You have a pad deposition problem. Try rebedding them per the instructions here and see if the problem goes away: http://www.zeckhausen.com/bedding_in_brakes.htm

If you want to understand the physics behind what is happeneing, read the following white paper: http://www.stoptech.com/whitepapers/warped_rotors_myth.htm
Your dealer service tech is not familiar Pad deposition.......yep.

I concur, they are not warped. This is why many folks use dedicated rotors for track and another set for street. Certain pads will coat a rotor with a very stubborn coating under severe duty temps that will not wear off at lower temps (street use). Some folks swap pad compounds for a short period to grind off the deposition after track use. There are a few notoriously abrasive, hard pad compounds that will wipe the deposition off very quickly and return the rotor to shiny-smooth condition. Some of these require you to clean your wheels off every day to avoid etching (lol).

The best solution I found was to match my race pads to a set of rotors dedicated for track-only. This offers the best of both worlds, aside from having to spend a couple hrs swapping hardware each time you go to the track. I generally drive to and from the track with the race brakes, but by Tuesday, I'm running with street brakes.

A set of soft street pads running rotors on track deposition will wear out "super fast".
 

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Lscman said:
A set of soft street pads running rotors on track deposition will wear out "super fast".
Please clarify this statement. Do you mean a soft street pad put on after a rotor has track pad disposition will wear out quickly? Or that street pads will wear out quickly on a track because of disposition problems?
 

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Stevus said:
Any chance the mechanic over torqued the wheel lugs? I wouldnt think so at a

BMW dealership, but ya never know.

There is always a chance of that.

From my experiences with BMW dealerships, most of them are excellent and staffed by qualified technicians... but occassionally, just like any service facility, there may be a ham-fisted or sloppy tech that did not pay attention.

When you're concerned about your BMW, and lug torque is a critical thing with these cars, it's not a bad idea to get a torque wrench of your own. A basic version is $29.99 at Sears:

http://tinyurl.com/5c2jl

- Rob
 
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