PC Valkyrie

Hi all. I think I have very straightforward question, and I hope there is a straightforward answer.

When I took my car for routine servicing a couple of months ago, I was told that my front rotors were "not up to spec", and they need to be replaced. Front brake pads were really low too (this I was not surprised about). I'm sure my occasional track days from the last 2 years contributed to the brake wear. They said I was fine for street use until the low brake pad warning comes on, so I didn't replace anything at the time, as I may go to aftermarket rotors.

Does anybody know what "spec" they are talking about?......I presume it may be the thickness of the actual rotor.

Bottom line: how does one determine whether the rotor needs to be replaced or not?

jturkel

hmmm......not sure about thickness. i replaced by rotors when i felt they were warped from breaking (i'm guessing this is how you tell its time if you arent a brake expert?)....and you'll know when they are warped. when you brake, it will feel at high speeds almost as if ABS is coming in. when my rear rotors were warped, breaking at high speeds virbrated my back window and seats....it was really obvious for me.

i'm sure someone can give you a better way to tell than me (and probably safer too lol)

ScottW911

I changed mine out, with the pads, when I felt the vibration and could run my finger on the (cool) rotors and feel a sizable raised lip on the outer edge. As to the spec thickness, I could not tell you. I am sure that splinter or boohooramblers have those specs somewhere.

Bottom line, I went with my gut and erred on the side of caution to replace them.

Also, as we know, the cross-drilled rotors can't be turned so, we end up replacing them earlier than most.

lkfoster

I don't know about Merc rotors, but Audi and BMW rotors have the minimum thicknesses cast into the hubs.

rockjock

You'll begin to see a lip form on the rotor on the inside section (towards the hub)-its usually time-also-technically speaking....rotors dont "wrap"-what generally happens is that pad material is deposited unevenly on the rotor(s) and generates the pedal feel-
thats why most guys at the track tell you not to stand on the brakes on pit-you simply heat up the material and melt it to the rotor-they're shot after that-
I usually go with new rotors every 2-3 years, or after 2 pad changes-

JonMBZ

MB does too, they are under spec if they are too thin when they put a measuring tool on them.

Emin

Has to do with thickness and wether they are warped or not. I had to change my front rotors about a week ago along with my pads

320 dreamer

rotors are measured from the inside to the outside edge with a micrometer. the thickness is cast into the rotor hub . exceed the minimum thickness and the need to be replaced. warped rotors can be turned as long as they meet the minimum thickness when straightened

splinter

Legitimate dealerships and competent independent technicians will furnish the measured pad and rotor thickness – and an estimated percentage of life remaining - to the customer before asking you to authorize their renewal. Certainly not suggesting that yours isn’t on the up and up. MB’s FSS and ASSYST service sheets have a dedicated section where the measurements are to be listed during the course of any inspection.

Brake service is typically a remunerative aspect of consumables service in most shops. DIY replacement is not an unpleasant Saturday morning diversion for several of us. Much easier on the MB than many other marques – including my GMC. Be that as it may, availing oneself of thorough and timely maintenance is inexpensive insurance against potential catastrophic failure. If they’re vibration-free and work well, there’s little rationale to swap in new pieces before the end of their useful service life is drawing near.

As you’re well aware, track use tends to dramatically hasten their demise. :)

Whose aftermarket rotors are you contemplating?

PC Valkyrie

Splinter, many thanks for the information. I don't intend to replace anything until I need to, but I suspect that time is coming soon for my front brake pads, and likely my front rotors.

I honestly don't know what rotors to use as replacements.....it could be stock C55 rotors, or other aftermarket brands. With the 135i in the stable, the C55 is seeing much less track days, but reducing unsprung weight with lighter rotors is always an attractive option. For sure, I want to keep the stock calipers. What do you suggest?

Panzerknacker

If you are going to do it yourself you might as well do the rotors when you do the pads. Saves you the trouble of taking it all apart again later just for rotors. www.partsgeek.com and www.partstrain.com have decent prices on what you need. I went with zimmerman rotors they seem to have a good reputation and are not overly expensive. I believe they are an OEM supplier for a number of automakers. Why not us a ceramic pad as well...

rockjock

I'd check out Evosport for a set to lessen weight-when I swapped mine I also switched from drilled to slotted all the way around-and ceramic pads (Axxis-not real happy with the dust still tho-3 days and the rims are almost black!)
SS lines and fluid-it was a 4 hour job in total for pads, rotors, lines, and fluid-but a great difference in the way the AMG brakes!

DHawk615

As a response to your original question, I'd have someone else besides the dealer check them out before you go buy new rotors. They could really need replacing, but i was reading in my manual the other day that MBZ always recommends changing the rotors when you do the pads on these cars, so they could just telling you you need new ones because its what they are "supposed" to do. Hope this helps.

splinter

There is no denying that the big brake upgrades from StopTech and MB’s SLK/CLK 030 package sure look pretty, but our relatively modest calipers have never failed to generate threshold deceleration forces on mine when called upon to do so.

Racing Brakes’ rotors have been universally well received, particularly on the BMW enthusiast forums – and by several of the track day ne’er do wells with whom I’ve made acquaintance. A few here have installed them and shared favorable feedback regarding their quality. Their front (only) rotors weigh approximately 18 pounds each as opposed to our ~25 lb anchors. Almost certain that the reduction in unsprung weight they provide is readily noticeable. No firsthand experience as those funds have been diverted toward my son’s tuition account.

Know it’s not a pad thread and not sure whose you’re utilizing, but I’ll put in another plug for Porterfield’s 847 (F) and 603 (R) R4-S pieces. Almost OE cold bite characteristics, minimal dust, and vastly improved dual-purpose fade resistance. Yet to find a better compromise with which to more fully exploit our original system. Of course, your CA and my CA may pose different ‘cold weather’ challenges.

When you have a spare moment, I’d certainly enjoy hearing about how your 135i gets around Canada’s picturesque circuits.

Racing Brakes
Porterfield

ohlord

mirror smooth with no ridges?
If so hand cross hatch sand them with 140 grit paper in a cross hatch pattern. Clean with brake cleaner and install akebono ceramic pads.
No one will resurface a Mercedes rotor,there simply is not enough material.
pm me if you want cryo -300f treated rotors,stop faster last 2-3 times longer.
work safe.
diy

look for unsprung weight reduction in rim choice.
Rotors don't yield much until you get into the several thousand dollars ea. ceramic units.