1998 E320 Rear Rotor Problem - PeachParts Mercedes-Benz Forum

Ferdman · #1 08-15-2004, 03:45 PM

Our pampered (virtually no city driving, mostly highway ... still on original front and rear brake pads) 1998 E320 with less than 29,000 miles has developed a vibration in the rear when braking at 60 - 70 mph. Today I pulled the rear wheels and noted that there are a series of radial marks on the rear rotors, some 20 marks spread around the braking surface of each rotor. Although it's difficult to see with the backing plate in the way it looks like matching marks are on the backside of the rotor. Are these marks very fine radial cracks, and are they commonplace on MB rear rotors? The part number for the rear rotors is 2104230612 with a minimum thickness of 8.3mm ... the rotors have very little wear.

Some 2 years ago I replaced the rear rotors on my parents' 1995 E320 with 30,000 miles because an independent mechanic mentioned that he noticed a rear vibration when braking at 50 mph. After removing the rear rotors I noticed radial cracks through each rotor and they were also warped. The mechanic suggested that the original owner likely drove with one foot on the brake pedal causing the rotors to overheat and crack. I don't ride the brakes when I drive I so I know that's not the cause of the rotor problem. Also, I only wash our cars when they are cool so I haven't hosed down hot rotors.

Ethan · #2 08-15-2004, 08:33 PM

they seem to me to be commonplace markings of rotors with 29K miles if the marks circle around disc.

by radial do you mean circular around disc or radiating form center outward?

do you see these marks on the front rotors.

before you go any further, do the basics and tighten everything up in the rear; spare wheel, jack, tool kit, battery - in rear or under seat.

spec the torque on the wheel lug nuts.

btw, there is still a bit of debate about cold water on hot discs, steady stream of cool water for example

whunter · #3 08-15-2004, 09:04 PM

You have a seven year old car.
Just the corrosion getting ground into the pads when you drive it will warp the rotors.
For the cost of rotors, why would you not change them?

As to the water on rotors question:
All the brake safety engineers in the industry would crackup over the question.
They are designed for natural weather conditions, which includes flooding and hard spray.
Yes, they do not last forever; they are not designed to...
These cars are made to DRIVE, not be a garage trophy.

Ferdman · #4 08-16-2004, 10:15 AM

Ethan, the marks are radial ... form the center outward. All components are tight and the lug bolts are, and have been, torqued properly with a torque wrench since the car was new.

whunter, the fact that the car is 7 years old does not mean that the rotors should be warped. Our 1991 (131,000 miles) and 1992 (89,000 miles) 300CE's still have the original unwarped rear rotors.

Kebowers · #5 08-16-2004, 08:11 PM

an unusual failure. Not unknown though. Replace them and go on with life. they are too cheap to worry about.

whunter · #6 08-16-2004, 08:22 PM

Quote:

Originally Posted by Ferdman

Ethan, the marks are radial ... form the center outward. All components are tight and the lug bolts are, and have been, torqued properly with a torque wrench since the car was new.

whunter, the fact that the car is 7 years old does not mean that the rotors should be warped. Our 1991 (131,000 miles) and 1992 (89,000 miles) 300CE's still have the original unwarped rear rotors.

True:
A seven year old rotor that has been stored in a box, with the correct protective oil coating should be perfect.

However:
A seven year old rotor that has been driven through weather conditions, and shows radial stress marks should at the least be checked for run out.
The odds are that it is either warped or corrosion has built up between the hub and rotor, thus taking it out of true.

This is natural and normal in aged cars, no reflection on the owner.

I do not resurface the rotors on my personal cars; the cost of new rotors is so low that it is not worth my time.

As to the 1991 (131,000 miles), I would never run a set of rotors that many miles, OEM durability testing and structural build design limits are 100,000 miles.
The stresses build up in the metal and you court disaster by exceeding the design and engineering limits of the structural material.
This is a safety issue, yours and other peoples; a new set of rotors is cheap insurance for your life.

Ferdman · #7 08-16-2004, 09:17 PM

whunter, if the life of a rotor is only 100,000 miles why doesn't MB recommend changing rotors every 100,000 miles? I've never read that advice anywhere or had the dealer Service Department recommend same and they're always looking for ways to make a buck.

whunter · #8 08-16-2004, 10:12 PM

that it is not on their watch list.
Most cars do not come back to the dealer after warranty ends.
Also, they don't check vehicle history, or assume the rotors where replaced during a previous brake service.
Trying to explain to a customer that the rotors have exceeded service life and should be replaced is not worth the effort, this thread in evidence.
For the same general reason, the calipers should be rebuilt every 100,000 miles.

Mercedes Benz does not care about anything over 100,000 miles; it is beyond vehicle service life.
To Mercedes Benz or any other OEM, a car over 100,000 miles is a dead issue that they want to fail at the earliest moment possible, preferably in a mechanically final manner, so they can sell you another and another, etc.

Quote:

Originally Posted by Ferdman

whunter, if the life of a rotor is only 100,000 miles why doesn't MB recommend changing rotors every 100,000 miles? I've never read that advice anywhere or had the dealer Service Department recommend same and they're always looking for ways to make a buck.

PHAEDRUS242 · #9 08-17-2004, 09:49 AM

Quote:

Originally Posted by whunter

I do not resurface the rotors on my personal cars; the cost of new rotors is so low that it is not worth my time.

On top of the cost issue, MB does not recommend resurfacing their rotors at any time for any reason.