Im having an issue with the brakes on my e3004w sport overheating when driving down from the ski resorts in colorado. The car will shimmy violently even on moderate braking. The service manager at my dealer says this is normal behavior, but I never had this issue with my w212 or w211. He suggests using more engine braking, but i feel like the cruise control should be able to handle a 6% downward grade at 60mph without shaking the car apart. Plus the small engine isn't much for engine braking. Anyone else having issues? The car has 4k miles.

 

NO CAR old or new should shimmy violently (your own words) on moderate to hard braking. bring it back to the dealership.

 

What usually happens is at some point ultra hot pad material has deposited unevenly on the rotors. This is most commonly caused by pulling up to a stop with stinking hot brakes and leaving your foot (of course) on the pedal at the bottom of a run. Always allow a cool off driving period after heavy use if at all possible and leave your foot off of hot brakes at all stops. (hand brake, as rears will not be as hot as the fronts, or put trans in park if you must wait on traffic)

Brakes work not on the metal of the rotor, but a very thin deposition of its own material. If this deposition layer is not super smooth, the subsequent use causes a radical pulsing in the pedal, especially if the rotors get heat in them suddenly again. Once that uneven deposition has occurred, it is not going away. Moderate to heavy braking will pulse the pedal (and the car) noticeably.

It is also possible to have this happen without a conscious situation of stopping with super hot brakes, but here is the point: Stock passenger brake pad material is not quite up to severe thermal cycling. No stock brake pad will survive this unless the brake rotors are larger and the pad material specially selected. This is not a case of consumer fraud, poor design nor bad performing brakes. If we make affordable brake systems that could withstand racing like brake conditions, we can then trust all customers to complain of squeaking brakes, pad dust and frequent pad and rotor replacement instead of the odd complaint of overheated brake pads discovered in pedal pulsing sensations.

This condition is commonly called "warped rotors", but is more often not really physical 'warp' of the rotor. While, it is possible to warp and even crack cast iron rotors through running them too thin due to old age and wear, more often it is a case of uneven pad deposition. In such cases, a measurement should be taken of rotor thickness. This may indicate it is sensible to replace the rotors that have become too thin due to wear. If not obviously in need of replacement, then very, very light pass with a brake lathe is needed to take off the uneven spots on the rotors and a good scuff job on the pads with carbon paper is in order. One should bed in the new rotor service with light to moderate braking for 200 miles, as per new brakes.

If doing a lot of exuberant down mountain driving, one could also consider a ceramic aftermarket front pad, such as Axis/PBR, EBC or Mintex. If available, an AXXIS ULT ceramic pad is a recognized street performance pad with excellent pedal feel and high temperature stability, low dust and good rotor wear. I am not sure what other pad to recommend for moderate performance or even if such a pad type is yet available for the W213 yet.

We do not want a 'track' or racing pad, just a good ceramic with wide heat range, just one step up from what ever grade MB has supplied. Such a pad may squeak slightly first thing in the morning, but they are not soft as to overheat and become a problem with uneven material deposition. This, as long as they are treated with the little bit of respect suggested here.

As one easily notes the AMG E63 versions have completely different, larger and much thicker rotors for added ventilation as well as much larger calipers and brake pads. The E43 probably has thicker rotors behind the visible four piston calipers. These pretty much can survive repeated stops and cool off quicker than standard brakes fitted to most passenger cars, the E300 included. They also add unwanted expense to brake service costs, never mind a couple thousand up front in the purchase price.

All in all, always cool down known extremely hot brakes before just standing still with your foot on them, no matter what pad is used or what the brake setup. It is also a good idea to warm up brakes for three or four medium stops before almost tripping the ABS every stop down a mountain road.

This said, it is surprisingly easy to overheat front brakes on any longish, twisty down hill section. I once took a 1991 Subaru Legacy GT down Decker Canyon (SRt 23). This famous twisty decent is about four miles long. With my parents in the car no less, at the bottom smoke was pouring off the front brakes. Needless to say, I knew to keep my foot off the brake pedal while waiting on PCH traffic to clear. My mother had a hoot doing it, surprisingly my father was a bit uneasy.

 

All true, however, Ive never heard of MBs suffering from this issue. On some Honda models, however, its quite common. I was able to bake the brakes on a mercedes SUV during a test drive. Doing so elicited fade but no "warping". If your issue persists your discs will have to be resurfaced. In the future Id use more transmission braking to give the brakes a break.

 

Let me try.....ha, ha.

BTW, it will not be something that would necessarily be noted immediately, rather next heavy brake use.

 

If it gets bad you will feel a slight vibration every time you apply the brakes moderately. Hopefully it wont get to that. Its one of the benefits of perforated or slotted rotors, better "outgassing".

 

Quality pads have long been baked in an autoclave as part of their manufacturing process, precisely to "degas" them. Ceramic compounds are particularly noted for their grip over a wide heat range do to non-production of gas.

 

Sounds like warped rotors to me...

 

One needs to look around on the forums. I have had the issue with my W204, and the V8 W212s were plagued by it. While Benz is not as bad as Honda in this regard, they are not immune.