'99 ML320 Minimum Rotor Thickness
 

I'm going to do a brake job on my '99 ML320 and was wondering what the minimum rotor thickness is for the vehicle. If I can get away with just replacing pads that would be great. Thanks for any help.

It varies based on the rotor's manufacturer. It will be stamped on the "hat" of the rotor, usually on the outside. Generally, you need to do a rotor change every time you do a pad change, that is the way they were designed. The only exception would be if you use ceramic pads, which are much easier on rotors (which is part of the reason they create less dust). Ceramics can go rotors every other pad change, depending on how you drive.

DCF is right in regard to the minimum thickness being stamped on the rotor. However, the rotors do not need to be replaced every time the pads are replaced. Simply measure the thickness of the rotors. If they are at, or above the minimum thickness, you can replace the pads only.;)

I agree it is not a REQUIERMENT that they be replaced every time, but I have never seen one running standard pads were the rotors were not shot every time the pads needed to be replaced (or so close to the minimum, it would be a wast to not change them when changing the pads). Measuring is certianly the best way to go.

It"s more like every other time, and I do alot of them.

IMHO, rotor replacement is a huge ripoff.

Original rotors should last 150-200k miles or more. I've never changed mine in almost 180k miles. If you change pads before they hit metal and make sure the caliper/piston travel is ok and nothing is stuck, rotors will wear evenly and last a long time.

If you don't like the cupping or lip and the edge, get the rotors turned. It costs a LOT less, and they will mic them for you and let you know if you hit minimum thickness.

be advised, rotors wear just like pads do, from my experience as a mercedes tech, it is usually for front brakes one set of rotors per two sets of pads is usually how it goes, it will have variances with driving styles,

No disrespest intended, but I hope I never see you in my rear-view mirror :eek:

None taken, but my rotors are fine and the vehicle stops on a dime.

Tell me what happens if you never replace them?

they wear thin, i have actually seen them so bad the center cooling fins are exposed on the rotor surface, you will eventually get pedal pulsations when braking and possibly will squeek, also as they wear the piston for the caliper has a longer throw and may either come out or get cocked to the side and not retract causing the wheel to lock, as stated above the rotors wear just as pads do, they are consumables

That would have to be the exception. The pads on those rotors must have been replaced every few months to get that kind of wear on rotors. I've never in my life seen rotors worn that thin. However, I'm not in the business that sees worn rotors every day.

Rotors are made from an extremely hard steel. Pads are made much, much softer. It's the pad that is supposed to be worn down, not the other way. As long as you don't let the pad get to metal, the rotor will last a very long time.

I'm not saying they don't wear. If they wear down enough, they may warp. Then it's time to replace. If you don't like the glazing, then get them turned. It only cost a few bucks to have it done. Much better than spending $60 a pop to replace them.

The other danger with letting the rotors wear to far is that as they wear they lose mass, and thus, the ability to disapate heat. Thinner rotors are FAR more likely to be warpped by heat, causing pedal "pulsing" and also poorer stopping distances. Now, if most of your driving is highway, you can get very long rotor life, as you are not using the brakes. Also, I use ceramic pads up front, which have noticed not only greatly reduced dust, but have also lasted for a lot more miles than OEM, and seem to be much easier on the rotors. Standard (OEM) pads ARE metal, as they have small metal fibers in the matrix. That is what causes the wear (and also helps wick away heat). Ceramics have no metal in them, thus, less "steel wool" action on the rotors.

Unless you run treated or aftermarket rotors, they are not hardened in any special way. While the castings are still hard, it is all relative.

Just for clarification, are you talking about MB rotors, or simply rotors in general?

In general. But my more recent years (10 yrs) have been predominately MB. I've replaced lots of pads, especially the organic ones on my 190E. Any rotors I've replaced have been on domestic cars when a piston/parking brake got stuck and one pad ground up the rotor.