How is brake pad wear measured? I have had two mercedes service centers give me different reports on my rear brakes. One says the shoes have 40% left. The other says only 20% remains. Is a tool used to measure pad thickness or is that an eye-ball opinion? I'd like to make my own evaluation and do my own pad/shoe replacement.

It sounds to me like they are making an uninformed guess.

Pad wear is a function of the resilience of the pads you use and your driving habits. Unless those technicians drive around with you and check the pads all day then there is no way in hell for them to tell the wear rate of your pads. There is no tool to my knowledge that does it either, this is one of the reasons why mercedes has a wear indicator for the pads.

I purchased my 420 about a month ago and I'm not, yet, fully aware of many of the operating details. Guess I need to read the owner's manual more closely. How does the wear indicator work?
Jerry

Basically if the front pads wear down beyond what mercedes has deemed a critical point the pad wear sensors which are connected to your pads will complete a circuit and activate an idiot light on the dash. You then should replace your front pads and have the rears inspected. Do read your manual.


What year and model do you have by the way? Is that an e420 or an s420? Let us know....

Yal,

Where did you get "wear rate" from? The question was the amount of wear of the pads, not the rate of wear.

lakelover,

I don't know what type of 420 you have, but FWIW, I have a new set of rear and front pads for my 1992 400e right here in front of me. The amount of brake material for the rear is 3/8 of an inch. The front is 7/16 of an inch. The metal backing on both are 3/16 of an inch.

The mechanics probably did a visual "estimation". I don't have access to my CD to find out what it the recommended minimum thickness, but the wear sensor should let you know that.

Hope this helps

I have a 1988, 420 SEL, @ 75K miles. It's the rear pads that I'm concerned about. The front pads and disks were replaced shortly before I bought the car. The pre-purchase inspection indicated 40% of the rear pads remaining. After buying the car I had the timing chain replaced and while the car was in the shop (Mercedes), the rear brakes were inspected, without my prompting. I was told that the rear pads had only 20% remaining and that the disks (or drums) are so thin that they should be replaced. BTW, I've put only a few hundered miles on the car. The mechanic doing the prepurchase inspection didn't mention the condition of the rear disks. Thanks for you comments. It's very helpful to have this resource to help me understand some of these technical things about our car. We love the car; it's the greatest car I've ever owned. Jerry

lakelover,

As a rule of thumb, I look at the brake pads lining material and compare it to the pads metal backing. If the brake pad lining material is 1/2 the thickness then it is time to replace the pads. If the lining material is less than 1/2 the thickness, then you have waited too long.

Your SEL may have different specs so you should look into getting a manual or CD as reference. But this is what is listed for my 400e:

Rear pad lining thickness (new): 11.0mm

Rear wear sensor trigger: 2.5mm
Min rear pad lining thickness: 2.0mm

So if your SEL has a rear wear sensor and it is working correctly, it should kick in well BEFORE the minimum thickness is reached.

Since they say the rotors are worn, then you might as well replace the rotors and pads in the rear. Not a difficult job.

Hope this helps.

David,

Thanks for the info. It's very helpful. I think I'll go ahead and replace the rear shoes and rotors.

Jerry

David,
"wear rate" or "wear of pads", I am not one to get into semantics here especially over words typed over the web. Technicians are always given out vague information to customers to get money and brakes are their favorite second only to the preverbial "tune up". I was just trying to help lakelover come to his own conclusions. Sorry if that bothered you.

Lakelover,
Glad someone finally read the post and gave you the info you were looking for didn't mean to take you off the wrong path.

Yal,

Thanks for the input. I welcome all the help I can get, and this forum has been most helpful: lots of knowlegable people eager to share their experience.

Jerry