Turning rotors. Myths and truths

anton28

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My 2008 cl63 AMG with 50k miles is due for a brake Job. The dealer tried telling me the rotors are not turntable because they are cross drilled. I told him that's bs as I've had plenty of cross drilled rotors turned without any issues. Then I'm told it's because euro cars use softer metals. Now the reason I'm even doing this research is because replacement rotors are 1,000 each. Yes I said 1,000 each. Now Ive spent alot of time on the Benz forums but all of those guys are clueless. So I'm on here to ask my viper brothers with race experience for some input. Do ero cars use diffrient material rotors and if so, can they be turned? Do I even need to turn the rotors if they are not warped, can I just get away with swapping new pads. Any input on this would be appreciated.
 

TowDawg

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When I had my E55, Merc said that none of their rotors are meant to be turned. Actually a lot of newer cars say the their rotors are not meant to be turned. My understanding is that the motors are basically made to the min thickness when new. This is mainly done to keep costs and weight down (less material), and help increase gas mileage to keep up with the tighter and tighter regulations (every little bit helps).
That said, what I usually do is this. If I didn't feel ANY type of vibration before changing pads, I would slightly scuff the old rotors with sandpaper (just to remove old brake pad buildup), and then put the new pads on. On the Benz, I did need new rotors, so I had to buy them. However, since it wasn't a car I tracking or "driving the **** out of it" (stressing the brakes), I bought a set of "bling" (slitted and drilled) rotors off of ebay for like $500 for all 4 (I think the dealership wanted something like $1600 to do the fronts only), and never had an issue with them. That is NOT something I would recommend if you drive the car hard, but for regular driving with the occasional "hammer down" acceleration runs only, they were fine.
The thing to remember with the Benz (I assume yours is the same) is that they can go through a "system check" if the key is even detected in the same area of the car, which includes a function check of the brakes. If this happens while you have the pads/rotors/calipers off, it could push the pistons right out of the calipers (or worse yet, smash your finger if it's in the way). What I was told (and I never lost a finger), was to leave the keys way the **** away from the car while your working on it, and don't even touch the door in attempt to open it, to avoid the possibility of the system cycling. ANother option is to disconnect the battery while doing the work, but I just made sure I didn't do anything that could "set it off".
 
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Dom426h

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When i first went to do a brake job on my GTS several years ago i could not find a place that turned rotors. They all told me the similar things; Back in the day it was more common to machine/turn because rotors were solid and/or thicker and/or more expensive. Also, for most cars rotors can be had for so stinkin cheap nowadays...

One downside to cutting the rotors is that you are removing material from the rotor. This will cause it to overheat quicker and be more likely to warp. Prob not an issue on most street driven vehicles but anyone that tracks will want that full thickness when threshold braking into turn1.

A machineshop showed me this thing called a flex-hone that they use to resurface flywheels and brakerotors. Its purpose is to remove the pad transfer layer from the rotor to have a clean consistant surface for the new pad to bed into. I purchased one and have used it eversince when changing pads. I dont change rotors on the Viper untill i see cracks which is usually after two or three years including 4 trackdays or so.


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bluesrt

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most euro cars cannot be turned, yesy they use a differant metal, more and more now days evan the big 3 cannot be turned(they wear like a brake pad) they are usually under spec evan before thinking about turning
 

AJ02

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Even if the rotors were able to be turned, you would be shooting yourself in the foot. I watched a video about it a few years ago. A car was set up with mechanically controlled gas and brake pedals for precise and repeatable control. It was then fitted with new pads and rotors and tested from 60 MPH. The next test was with turned rotors and new pads. The stopping distance increased. According to the people doing the test, this was due to the fact that new rotors have a "crosshatch" patterned finish and once you turn them, they have a "linear" pattern finish. The crosshatch gives more "grip" to the pads.
 

AZTVR

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Even if the rotors were able to be turned, you would be shooting yourself in the foot. I watched a video about it a few years ago. A car was set up with mechanically controlled gas and brake pedals for precise and repeatable control. It was then fitted with new pads and rotors and tested from 60 MPH. The next test was with turned rotors and new pads. The stopping distance increased. According to the people doing the test, this was due to the fact that new rotors have a "crosshatch" patterned finish and once you turn them, they have a "linear" pattern finish. The crosshatch gives more "grip" to the pads.

I am no expert; but, have done a lot of reading. Their explanation above, of the cause of their test result explanation sounds like BS to me. However, I believe the result. To me, it is more likely that they did nothing to "bed in" the new pads and brake surfaces. Brakes are more effective when there is a layer of compatible brake material on the rotor. I can post up some links to some technical explanations if desired. That's why you need to bed in new pads and rotors. For me, if I have no vibration, and I am replacing pads with the same material, and the rotors are in spec, I DO NOT resurface the rotors. If I am replacing with a different material, then I scuff off the old material from the rotor and then bed in the new setup like I would do with new rotors. I believe that "commercial" mechanics use turning of the rotors as an easy way to remove the old brake material and ensure no call-backs but, it is not necessary as a matter of course.

I am a shadetree mechanic, so take my input for what it is worth.

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

[URL]http://www.essexparts.com/learning-center/cat/brake-rotors/post/Bed-in







[/URL]
 

AJ02

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I totally agree with the bedding in process. I put the Stoptech Big Brake system on my GTS and "bedded" the pads in according to the instructions. The difference before bedding and after is night and day. The aforementioned reference was just to illustrate the difference between new rotors and turned ones, not taking in account the bedding in process. Their explanation was that with the turned rotors, the linear cutting of the rotors took away the "roughness" as it were and the pads didn't have as much to grip. I'm no professional mechanic either, but it seemed like a feasible explanation to me.
 

MoparMap

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Seems like any rough surface on the rotor would get filled in with pad material transfer during the bedding procedure to me, but perhaps not. Maybe if you're keeping your brakes in tip top shape and replacing everything frequently it might make a difference, but I'd think a few hard sessions at a track would pretty much flatten out any surface fairly quickly.
 

Hirkophoto

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When i first went to do a brake job on my GTS several years ago i could not find a place that turned rotors. They all told me the similar things; Back in the day it was more common to machine/turn because rotors were solid and/or thicker and/or more expensive. Also, for most cars rotors can be had for so stinkin cheap nowadays...

One downside to cutting the rotors is that you are removing material from the rotor. This will cause it to overheat quicker and be more likely to warp. Prob not an issue on most street driven vehicles but anyone that tracks will want that full thickness when threshold braking into turn1.

A machineshop showed me this thing called a flex-hone that they use to resurface flywheels and brakerotors. Its purpose is to remove the pad transfer layer from the rotor to have a clean consistant surface for the new pad to bed into. I purchased one and have used it eversince when changing pads. I dont change rotors on the Viper untill i see cracks which is usually after two or three years including 4 trackdays or so.


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Honing the brakes with this tool will not fix a warped or un evenly worn rotor. This only cleans the surface and prepares it for the new pads. It's a good thing to do but only if your rotors are in good shape. This will not help bad rotors. I have one of these too, they work great to prepare the disc when changing pads.
 
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anton28

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There isnt a cheaper version of a brake rotor I can get on ebay or anywhere else for that matter. Factory stuff from the dealer is 1k each. I can get a race upgrade from a performance company for 3500 for all 4 rotors and pads. But this car is just my weekend driver. Sounds like I can just replace my pads if Im using the same pad as i have now and not worry about even touching the rotors. I don't do any type of heavy driving.

Thanks for all the great info guys. I knew I could count on my Viper community for some great info!!!
 

TowDawg

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For cheap, street only stuff, Ebay is your friend.
http://www.ebay.com/sch/i.html?_sacat=0&_from=R40&_nkw=2008+c63+brake+rotor&_sop=15

Your stock rotors might be 2-piece (I'm not intimately familiar with the newer Benz's), but even if they are, I don't see a reason you couldn't switch to a 1-piece rotor. It's going to weigh a little more, but for normal, everyday driving, who cares?

Check the link above, and there's all kinds of options for "bling" rotors. You can get all 4 rotors and pads for under $650.
I'm not endorsing these rotors, but they're the same "type" ones I used on my 55 in the past and never had an issue.
 
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anton28

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For cheap, street only stuff, Ebay is your friend.
http://www.ebay.com/sch/i.html?_sacat=0&_from=R40&_nkw=2008+c63+brake+rotor&_sop=15

Your stock rotors might be 2-piece (I'm not intimately familiar with the newer Benz's), but even if they are, I don't see a reason you couldn't switch to a 1-piece rotor. It's going to weigh a little more, but for normal, everyday driving, who cares?

Check the link above, and there's all kinds of options for "bling" rotors. You can get all 4 rotors and pads for under $650.
I'm not endorsing these rotors, but they're the same "type" ones I used on my 55 in the past and never had an issue.

Not the same car. I appreciate the effort. I have a CL63 not c63. Completely diffrient setup, even from the older cl55's. Trust me, I've searched far and wide lol. There is nothing out there cheaper then 3k, factory stuff being 4k.
 

TowDawg

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Oops! Missed the lower case "l" in your first post.
SON OF A *****! Those things ARE expensive!
I turned up some mid to high $700 prices with a quick search, so it's better than the dealer, but I had no idea there were brakes out there that are that expensive for the cheapest ones (that aren't carbon).
 
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anton28

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Oops! Missed the lower case "l" in your first post.
SON OF A *****! Those things ARE expensive!
I turned up some mid to high $700 prices with a quick search, so it's better than the dealer, but I had no idea there were brakes out there that are that expensive for the cheapest ones (that aren't carbon).

Yeah I found those as well plus. Shipping is another 250 per pair so were down to 3600 from 4K. Just for replacement rotors lol. Blahhh
 

Bugman Jeff

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I've done many a brake job in my day. Unless the rotors are warped or grooved I don't feel that turning is necessary. Even with a little bit of grooving, the new pads will quickly wear down to conform to the rotors. The finish on the rotors doesn't matter much, after a few thousand miles, it will be worn smooth anyway.
 

TrackAire

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I've done many a brake job in my day. Unless the rotors are warped or grooved I don't feel that turning is necessary. Even with a little bit of grooving, the new pads will quickly wear down to conform to the rotors. The finish on the rotors doesn't matter much, after a few thousand miles, it will be worn smooth anyway.

A lot of the Mercedes cars have sensors that tell you the condition of the brakes.....you end up with constant reminder on your electronic information center that I believe can only be cleared by the dealer. My wife only made it to around 23000 miles on her ML550 before the pads needed replacement and a billboard message on the info center reminded you of such....on every start up. The dealer only to replace pads, rotors were fine.

A 1963 Corvette is sounding pretty good right now, lol.

George
 

TAXIMAN1

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As the previous owner of several AMG cars (2 E55's,SL55,E63,CLK55) (keyword: previous, never again). I can tell you there are very few cars (maybe Lambo and Ferrari,etc, but thats about it) that are more expensive to maintain. The cars are an absolute warranty and maint. nightmare (not to mention depreciation nightmare, due to the aforementioned).

Do you "have" to repalce the rotors in order for the car to drive? No, of course not. Will the car loose some stopping performance from factory spec? yes.

Bottom Line. Mercedes sets these cars up with absolutely ZERO (and I mean ZERO) consideration for maint. costs. Their position is, if you cant afford (or dont want to pay up) for new rotors at the time of a brake job on an AMG car.. Then, its probably time to sell the car or decide not to buy one....

I'm Not saying thats right or wrong, thats just their postion (and Audi and BMWM cars as well).

The dealer will not resurface, because it is not what the factory "recommends", and they would be in violation of their franchise contract. If they were to do this. There is instant liability if you were to have a wreck.
 

TowDawg

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You can reset the sensors yourself. I can't recall how off the top of my head, but I know I never took it in to have it done. Basically the pad has a little cut-out in it that the sensor fits into. Once the pads wear down and the sensor touches the metal of the rotor, it sets off the warning light. No voodoo to it. lol
 

ViperJohn

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You can reset the sensors yourself. I can't recall how off the top of my head, but I know I never took it in to have it done. Basically the pad has a little cut-out in it that the sensor fits into. Once the pads wear down and the sensor touches the metal of the rotor, it sets off the warning light. No voodoo to it. lol

That's interesting, I would have thought you would have to go into computer and reset.
 

Chuck 98 RT/10

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No need to turn them. Use the 3M kit and then bed them properly.
You don't need new rotors until you have cracks like this...

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