Disk brake wear.
 

I have no way of measuring them but I am getting ready to replace the pads. When I run my finger over the disk, I noticed that there is about a 1 mm ridge at the edge. Do these disks have life in them or do they need to be replaced?

Thanks.

OH, this is on the 124.

You should measure them, cheap tool, available just about anywhere, and then get the minimum spec, which may be stamped on the rotor. I wouldn't replace a rotor for a small lip. If it causes a problem you can have it taken off by anyone that turns rotors.

My W210's were stamped 25.4mm new and 21.4mm(?) min.

Yours may be different.

Don't have the rotors turned. The small lip is no problem. Check with an independent MBZ mechanic on the minimum thickness.

I just put new pads onto the wagon about 3 days ago...



Both of the brake rotors had that little lip at the edge of the disk, and its caused no problems...

I agree, I wouldn't worry about a 1mm lip. As long as the rotors aren't warped, and this is the second set of pads, you should be fine.
But, if you think you might not be able to sleep at night, then by all means, have them measured.

The rotors are considered "sacrificial" meaning that they are never machined, just replaced when the min thickness is exceeded. Usually 3 pad replacements to one set of rotors. Fronts wear 3 to 4 times faster than the rears. Thats why the wear sensors are only on the front pads.

But a lip like that can cause a problem, and it's easy and safe to take it off. The MB view that rotors should not be turned is consistent with their desire to sell more rotors. They know they can't change the laws of physics but they also know they could proclaim that underwear is to be worn on the outside, and some people would do it.

On a W210 the minimum pad thickness is 2mm. Terry's values include the backing plate. The wear sensors (if you have them) are 3mm thick so that's the point they'll go off giving you a little time to have the brakes serviced. I don't have the values for your car but they would be in a factory service manual. If you post in a W124 subforum such as on www.benzworld.org, I think you'll get the exact values.

If you want you can pick up a cheap micrometer at Harbor Freight for about $20-30 which will be more than accurate enough. You'll have to convert from inches to metric at some point. (1/1000th of an inch = 0.0254mm) Check each rotor at 4 positions about 90 degrees apart and average. Check the pads at two positions in from each end and average.