Rust Spots Rear Rotors: Necessarily Indicative of a Problem?
 

Yesterday I had the snows removed and the regular tires put on....92 300D. The tech made the comment that it didn't look like the rear calipers were engaging because of rust SPOTS on the surface of both rear rotors (the spots are evenly distributed over the surface, but there's still plenty of bare metal to be seen). This is a car driven every day so I was surprised to see the spots. And on my 91 300D (same driving patterns....if anything driven less) the rotor surfaces were perfectly clean. So I'm thinking I might be needing new calipers.

As it's due for a state inspection, I set an appointment (different shop). I mentioned the brake issue and the tech that rust spots on the rear are not necessarily indicative of a problem.

What are anyone's thoughts?

could be leftover damage from PO driving with the rivets grinding on the rotor...
got pics?

I'm the one who last had rotors and pads replaced....at 210k, now has 242k.

No pics....son gone for day with car. Maybe I can take some later.

pics would help sure.

My 190E's rotors would rust up a bit after a rain and me not driving for a day or two. They would clear up after some driving though. Miles down the road I replaced the rotors with some R1 Concepts units that have zero rust even after sitting all winter.

Here's a pic:

One thing to notice in the pic: there's an inner band with no rust. So it looks like the pad is making contact there but not on the rest of the rotor?

Hmm I'd pop the wheel off and take a look at the pad itself. Kinda odd only one area of the pad to contact the rotor.

Agreed, I would think that rotor would be polished shiny.

I think you have poor pad-to-rotor contact at that wheel.

Brake hose restriction??

totally typical of a seized piston. time for replacement/rebuild...

the reason it's touching in that one spot, is the caliper is TWISTING THE ROTOR each time you hit the brakes hard... because only the opposite piston is making contact.

I would also recommend replacing the brake hoses while you're down there, especially if they've not been done before and they are 20+ years old...

Thanks, guys....after 21 years and a car I plan to keep forever, new calipers and hoses (and pads and rotors) seems like a no-brainer.

Actually you could put some stainless steel lines on in place of those rubber ones! They're not too pricey either!

I've got these on my 300D and the brakes are most excellent!

WRXtra

WRXtra

I just recently experienced similar on my 190 on a rear. Was my first time into MB brakes. Thought it was really strange that only the outside pad was worn until I removed the caliper and realized there was a piston on both sides unlike the typical car with a single piston. Was definatley over-engineering as the pads themselves were tiny.

How has the car felt under different braking applications? That should Have been something you could discern, unless the car has been stopping strangely for a long time, and you just didn't notice it.

Time for a rebuild. Sumpthin's not makin contact right.......