noticeable lip on front rotors, time to replace?
Thread Starter
Senior Member
Joined: Apr 2014
Posts: 332
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2007 GL450
noticeable lip on front rotors, time to replace?
A noticeable lip along the perimeter of front rotors, on my 2007 GL450.
Braking feels fine, steady and strong, no vibration.
The rotors were never changed, on the 2nd set of brake pads, maybe 30% through this 2nd set of pads.
Planning to replace the front lower control arms (cracks on lower control arm rear bushing), maybe its a good time to get the rotors replaced, since the rotors need to be removed for the job anyway.
Braking feels fine, steady and strong, no vibration.
The rotors were never changed, on the 2nd set of brake pads, maybe 30% through this 2nd set of pads.
Planning to replace the front lower control arms (cracks on lower control arm rear bushing), maybe its a good time to get the rotors replaced, since the rotors need to be removed for the job anyway.
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Joined: Jun 2010
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From: Emmett, ID, USA
2007 GL450
People worry too much about thickness. They should worry about thickness variation - high spots. That actually is what causes discs to be perceived as "warped".
It is very difficult to mount the discs flat enough on a lathe to turn them properly. I watched Rainman Ray proudly turn "warped" rotors; he was marveling at how "out-of-flat" they were, not stopping to wonder if the jig he had them on was holding them flat. Hey, he's a mechanic, not a machinist.
If the discs are not making the steering wheel shudder when you brake, I wouldn't worry about thickness. Yeah, you have a little less iron to absorb the heat transient when you brake, and your caliper piston will extend a little further, but neither of these is that big of a deal. On the other hand, I don't think I'd change the pads without changing the rotors; they just don't cost that much.
And there is no point to getting fancy rotors unless you enjoy the fancy; cast iron is cast iron. Dimpled and slotted rotors do look cool, but are worse for off road because they hold abrasive dirt.
Do, however, make a gentleman's effort to bed-in the pads; you want the rotors to be a shade of gray, not shiny iron. This will greatly prolong the rotors' life.
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From: Albuquerque
'10 CL550, '12 GL550
The maximum permitted wear is 2 mm
If you can feel a lip, it’s pretty certain it’s at least 1 mm. … and of course there is one on the back side of the rotor, too. The lip indicate how thick the rotor was when new. With a lip, all metal inboard of that lip is gone.
it’s senseless to think machining can restore thickness. There is no machining of Mercedes rotors authorized.
With these vehicles it’s basically common to replace pads and rotors at the same time, every time. New pads are really thick and they will very likely last as long as the rotor. Of course you shouldn’t put used pads next to a new rotor. If you do replace just pads, it’s almost certain rotor will reach wear limit prior to those pads wearing out.
When you replace a rotor, you must remove the caliper and the caliper holder bracket. Mercedes specifies that screws that mount the holder be replaced with new screws. Screws come with encapsulated thread locker applied.
If you can feel a lip, it’s pretty certain it’s at least 1 mm. … and of course there is one on the back side of the rotor, too. The lip indicate how thick the rotor was when new. With a lip, all metal inboard of that lip is gone.
it’s senseless to think machining can restore thickness. There is no machining of Mercedes rotors authorized.
With these vehicles it’s basically common to replace pads and rotors at the same time, every time. New pads are really thick and they will very likely last as long as the rotor. Of course you shouldn’t put used pads next to a new rotor. If you do replace just pads, it’s almost certain rotor will reach wear limit prior to those pads wearing out.
When you replace a rotor, you must remove the caliper and the caliper holder bracket. Mercedes specifies that screws that mount the holder be replaced with new screws. Screws come with encapsulated thread locker applied.
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Member
Joined: Nov 2018
Posts: 139
Likes: 37
From: Portland, OR
GL320 CDI
Nobody thinks this. Not one person. "Turning" rotors removes a layer of pad transfer compound to achieve a fresh flat mating surface. Proper bedding and heat cycling will ensure braking performance does not degrade.
MBWorld Fanatic!
Joined: Jun 2010
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From: Emmett, ID, USA
2007 GL450
Kudos to you for understanding the "bedding" process. A minor correction: You don't want to remove the pad compound transfer layer, unless it is unevenly applied or is only on high spots.
Ideally, the friction interface is between the pad and the transfer layer - but this is a bit difficult to maintain. One has to repeat the bedding-in process regularly if the pads are not used up to the temperature at which pad compound is transferred. Few of us regularly get the brakes hot enough to maintain the layer. It is a shame because the rotors could last a very long time if the transfer layer were maintained.
One can get thickness variation just from uneven pad material deposition. Interrupted early enough, those high spots can be fixed, but if neglected, can lead to cementite inclusions, which are iron carbide, and much harder than the surrounding cast iron. These can be machined off, but in my experience are difficult to handle. I tried using semi metallic pads for this purpose, and even after abrading several thou of rotor, some inclusions were still there, manifesting as blotches on the rotors.
This post explains how to manage street brake pads and rotors: https://www.clublexus.com/forums/mai...disc-myth.html
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From: Melbourne, Australia
2010 ML550 VIN WDC1641722A564750, 2010 B180
The rotors have a standard depth of 32mm when new. Once they fall below 29mm, they are out of spec and should be changed. Measuring them requires a caliper that hurdles the lip created by rotor wear. These rotors cannot be refinished.
MBWorld Fanatic!
Joined: Jun 2010
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From: Emmett, ID, USA
2007 GL450
Tape washers on each side of the caliper's jaws, and then zero the calipers.
Junior Member
Joined: Feb 2021
Posts: 21
Likes: 5
From: Cazenovia / Chicago / Wokowice
2010 GL450 , 2005 Sprinter 3500, 1980 SL 500
NEVER EVER INSTALL Slotted / vented or drilled rotors on an SUV, I did on my 2010 GL450 and my chevy suburban, thinking they were "performance upgrades", the vehicle is simply too heavy for an engineering concet designed around a sportscar whose weight was reduced down to insignificant.
MBWorld Fanatic!
Joined: Jun 2010
Posts: 2,755
Likes: 628
From: Emmett, ID, USA
2007 GL450
NEVER EVER INSTALL Slotted / vented or drilled rotors on an SUV, I did on my 2010 GL450 and my chevy suburban, thinking they were "performance upgrades", the vehicle is simply too heavy for an engineering concet designed around a sportscar whose weight was reduced down to insignificant.
FYI the OEM front rotors are vented. That's what it means to have the hollow core and centrifugal vanes.
There is only one reason to not install slotted or dimpled rotors: If they capture mud, the sand in the mud will abrade the rotors. Cross drilled rotors would at least allow the mud to eject into the center vents. Better to have flat discs, and the pads will wipe away the mud.
That, and the cost for something generally unnecessary. Slotting, drilling, and dimpling serve to vent away the gases released by vaporizing pad material binder. This ventilating the pad surface is useful for reducing brake fade when the pads and rotors are getting gutenhot. You want a little extra margin for heat accumulation when braking into the corner. If you like to drive your GL like it is a track car, well, have at it.
If you routinely tow heavy loads down long steep hills, you should first learn how to use brakes - pulse, don't ride - to lessen overheating, and also learn to downshift at the start of a descent.
But there is absolutely nothing preventing you froum running slotted, drilled, or dimpled rotors if that is your fancy. I did for about 100k miles and then realized the mistake when I found out how fun it is going off road in the GL.
Junior Member
Joined: Feb 2021
Posts: 21
Likes: 5
From: Cazenovia / Chicago / Wokowice
2010 GL450 , 2005 Sprinter 3500, 1980 SL 500
I have had shops refuse to turn these rotors. Haven't gotten one to do it, in fact. I guess MB dictated from Mt. Sinai that thou shalt not turn these rotors.
People worry too much about thickness. They should worry about thickness variation - high spots. That actually is what causes discs to be perceived as "warped".
It is very difficult to mount the discs flat enough on a lathe to turn them properly. I watched Rainman Ray proudly turn "warped" rotors; he was marveling at how "out-of-flat" they were, not stopping to wonder if the jig he had them on was holding them flat. Hey, he's a mechanic, not a machinist.
If the discs are not making the steering wheel shudder when you brake, I wouldn't worry about thickness. Yeah, you have a little less iron to absorb the heat transient when you brake, and your caliper piston will extend a little further, but neither of these is that big of a deal. On the other hand, I don't think I'd change the pads without changing the rotors; they just don't cost that much.
And there is no point to getting fancy rotors unless you enjoy the fancy; cast iron is cast iron. Dimpled and slotted rotors do look cool, but are worse for off road because they hold abrasive dirt.
Do, however, make a gentleman's effort to bed-in the pads; you want the rotors to be a shade of gray, not shiny iron. This will greatly prolong the rotors' life.
People worry too much about thickness. They should worry about thickness variation - high spots. That actually is what causes discs to be perceived as "warped".
It is very difficult to mount the discs flat enough on a lathe to turn them properly. I watched Rainman Ray proudly turn "warped" rotors; he was marveling at how "out-of-flat" they were, not stopping to wonder if the jig he had them on was holding them flat. Hey, he's a mechanic, not a machinist.
If the discs are not making the steering wheel shudder when you brake, I wouldn't worry about thickness. Yeah, you have a little less iron to absorb the heat transient when you brake, and your caliper piston will extend a little further, but neither of these is that big of a deal. On the other hand, I don't think I'd change the pads without changing the rotors; they just don't cost that much.
And there is no point to getting fancy rotors unless you enjoy the fancy; cast iron is cast iron. Dimpled and slotted rotors do look cool, but are worse for off road because they hold abrasive dirt.
Do, however, make a gentleman's effort to bed-in the pads; you want the rotors to be a shade of gray, not shiny iron. This will greatly prolong the rotors' life.
Junior Member
Joined: Feb 2021
Posts: 21
Likes: 5
From: Cazenovia / Chicago / Wokowice
2010 GL450 , 2005 Sprinter 3500, 1980 SL 500
where do you get these ideas
FYI the OEM front rotors are vented. That's what it means to have the hollow core and centrifugal vanes.
There is only one reason to not install slotted or dimpled rotors: If they capture mud, the sand in the mud will abrade the rotors. Cross drilled rotors would at least allow the mud to eject into the center vents. Better to have flat discs, and the pads will wipe away the mud.
That, and the cost for something generally unnecessary. Slotting, drilling, and dimpling serve to vent away the gases released by vaporizing pad material binder. This ventilating the pad surface is useful for reducing brake fade when the pads and rotors are getting gutenhot. You want a little extra margin for heat accumulation when braking into the corner. If you like to drive your GL like it is a track car, well, have at it.
If you routinely tow heavy loads down long steep hills, you should first learn how to use brakes - pulse, don't ride - to lessen overheating, and also learn to downshift at the start of a descent.
But there is absolutely nothing preventing you froum running slotted, drilled, or dimpled rotors if that is your fancy. I did for about 100k miles and then realized the mistake when I found out how fun it is going off road in the GL.
FYI the OEM front rotors are vented. That's what it means to have the hollow core and centrifugal vanes.
There is only one reason to not install slotted or dimpled rotors: If they capture mud, the sand in the mud will abrade the rotors. Cross drilled rotors would at least allow the mud to eject into the center vents. Better to have flat discs, and the pads will wipe away the mud.
That, and the cost for something generally unnecessary. Slotting, drilling, and dimpling serve to vent away the gases released by vaporizing pad material binder. This ventilating the pad surface is useful for reducing brake fade when the pads and rotors are getting gutenhot. You want a little extra margin for heat accumulation when braking into the corner. If you like to drive your GL like it is a track car, well, have at it.
If you routinely tow heavy loads down long steep hills, you should first learn how to use brakes - pulse, don't ride - to lessen overheating, and also learn to downshift at the start of a descent.
But there is absolutely nothing preventing you froum running slotted, drilled, or dimpled rotors if that is your fancy. I did for about 100k miles and then realized the mistake when I found out how fun it is going off road in the GL.
Off road in a GL? you must have regular shocks on the 2008 and not the self leveling bladders and compressor that would sot more than the blue book of my car to replace. If it pops and levees you in a bottomed out and non drivable state, I dont even want to think about it after the range rover nightmare I went through...
I am no brake technology engineer, however I ordered a set of drilled and slotter rear rotors for my GL and suburban from rock auto, .. to match the fronts like you mentioned... and something just has not been right ever since with either of the cars. When I drive other vehicles in the family that are solid disks they have better braking performance so I blamed the rotors and came up with my own theory... after reading that GT500 brake engineers article a few times I am questioning what else could have happened.... thinking that in order to bed in the rears I would have to over temp the fronts..... and thus never being able to reach equilibrium on all 4 tires.
MBWorld Fanatic!
Joined: Jun 2010
Posts: 2,755
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From: Emmett, ID, USA
2007 GL450
"where do I come up with them" are you jealous or something? Mavbe I am over thinking it, maybe I have observed a change and do not understand the cause... think it's strange how your replies to others a bit insulting, but if you need that, I can take it... in my world there are no dumb questions.
Off road in a GL? you must have regular shocks on the 2008 and not the self leveling bladders and compressor that would sot more than the blue book of my car to replace. If it pops and levees you in a bottomed out and non drivable state, I dont even want to think about it after the range rover nightmare I went through...
I am no brake technology engineer, however I ordered a set of drilled and slotter rear rotors for my GL and suburban from rock auto, .. to match the fronts like you mentioned... and something just has not been right ever since with either of the cars. When I drive other vehicles in the family that are solid disks they have better braking performance so I blamed the rotors and came up with my own theory... after reading that GT500 brake engineers article a few times I am questioning what else could have happened.... thinking that in order to bed in the rears I would have to over temp the fronts..... and thus never being able to reach equilibrium on all 4 tires.
Off road in a GL? you must have regular shocks on the 2008 and not the self leveling bladders and compressor that would sot more than the blue book of my car to replace. If it pops and levees you in a bottomed out and non drivable state, I dont even want to think about it after the range rover nightmare I went through...
I am no brake technology engineer, however I ordered a set of drilled and slotter rear rotors for my GL and suburban from rock auto, .. to match the fronts like you mentioned... and something just has not been right ever since with either of the cars. When I drive other vehicles in the family that are solid disks they have better braking performance so I blamed the rotors and came up with my own theory... after reading that GT500 brake engineers article a few times I am questioning what else could have happened.... thinking that in order to bed in the rears I would have to over temp the fronts..... and thus never being able to reach equilibrium on all 4 tires.
"drilled and slotted ... to match the front"? The factory rotors are vented front and rear, with no slots, dimples, or drilled holes - so it is not clear what you did. In any event, the rear brakes just don't provide that much of the braking, so I am guessing something else changed. If you are really picky about braking ... dunno ... possibly it has to do with the type of steel ... one point about drilled and slotted, they do reduce the face area of the disc ...
Popping air springs is a problem whether you are on road or off. Check them for leaks on a preventive basis.
Last edited by eric_in_sd; Feb 8, 2023 at 03:06 PM.
MBWorld Fanatic!
Joined: Jun 2010
Posts: 2,755
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From: Emmett, ID, USA
2007 GL450
Although I installed the same pads on my daughter's Jeep and managed to get a very nice gray layer on the rotors, so I dunno.
Thread Starter
Senior Member
Joined: Apr 2014
Posts: 332
Likes: 70
2007 GL450
I did a search on internet and found out that Zimmermann brake rotors have good reputations.
Ordered two Zimmermann rotors for my GL450 at $92 each from FCP euro, instead of Genuine Mercedes rotor at $101 each.
Rotors were delivered, made in Germany. They look nice and are pretty heavy.
Ordered two Zimmermann rotors for my GL450 at $92 each from FCP euro, instead of Genuine Mercedes rotor at $101 each.
Rotors were delivered, made in Germany. They look nice and are pretty heavy.
Member
Joined: Nov 2018
Posts: 139
Likes: 37
From: Portland, OR
GL320 CDI
[QUOTE=Mark Pasieka;8716419I am no brake technology engineer[/QUOTE]
This is clearly quite true. So please stop speaking as if you understand what you are talking about.
This is totally incorrect. It sounds like you are well meaning, but you are terribly misinformed about braking and driving offroad (where EVERYTHING breaks). Slotted, drilled, or drilled + slotted rotors are nothing more than physics applications based upon vehicle use. If anything a slotted/grooved rotor will decrease braking distance and help keep pads from glazing. The only downside to a slotted rotor is that you may use pads faster. Interestingly enough, drilled rotors are the least effective because they reduce the mass of the disc and thus the total size of the heat fin's ability to disperse heat. The top SCCA racers will use generic blank brake discs for this reason.
If you are interested in leveling up your knowledge, a great resource for learning about brake components and characteristics is StopTech (although it appears they have been acquired by braking gian, Centric). Here's their tech document about bedding pads and it has some great information about the physics of braking https://www.centricparts.com/media/t...e-8-2018_1.pdf
This is clearly quite true. So please stop speaking as if you understand what you are talking about.
NEVER EVER INSTALL Slotted / vented or drilled rotors on an SUV, I did on my 2010 GL450 and my chevy suburban, thinking they were "performance upgrades", the vehicle is simply too heavy for an engineering concet designed around a sportscar whose weight was reduced down to insignificant.
This is totally incorrect. It sounds like you are well meaning, but you are terribly misinformed about braking and driving offroad (where EVERYTHING breaks). Slotted, drilled, or drilled + slotted rotors are nothing more than physics applications based upon vehicle use. If anything a slotted/grooved rotor will decrease braking distance and help keep pads from glazing. The only downside to a slotted rotor is that you may use pads faster. Interestingly enough, drilled rotors are the least effective because they reduce the mass of the disc and thus the total size of the heat fin's ability to disperse heat. The top SCCA racers will use generic blank brake discs for this reason.
If you are interested in leveling up your knowledge, a great resource for learning about brake components and characteristics is StopTech (although it appears they have been acquired by braking gian, Centric). Here's their tech document about bedding pads and it has some great information about the physics of braking https://www.centricparts.com/media/t...e-8-2018_1.pdf
