New brake discs corroded after 16500 miles-is this normal?

spiritus

We purchased an approved used Mercedes C200 nearly 18 months ago and it is now in for it's second service.
Inspection says brake discs are heavily corroded and scored on both sides and recommendation is to replace. Been quoted £ 553 by the dealership!
I am awaiting a quote from an independant but they told me that brake pads would need to be replaced at the same time as it's good practise not to put old pads onto new discs. I'm surprised the dealership didn't suggest this either as they rarely miss an opportunity to get more money from the customer.
Is it normal for a 3 year old car that has done 16500 to need new discs. Last year when the car was only 2 yrs old and probably around 13500 on the clock the dealers told us it needed new rear brake discs and pads.

AdrianC

Only doing 3k in the last year certainly won't help one tiny bit...

Can you see the discs through the wheels? If so, what did they look like?

daveyjp

It can be an issue on cars which don't do many miles.  Disks are only mild steel and therefore rust.  On vented disks in particular water gets in between the fins and corrodes them if the car isn't driven.  Rear brakes can be worse as they are hardly used during normal driving.

You are however right to get a second opinion.  An indie should be less than half the cost for disks and pads.

The_Rainmaker

Rear discs always need replaced sooner because the braking is weighted towards the front wheels and the back discs corrode more.  When I had a 230E the rear discs were replaced every second year. I wouldn't be paying a main dealer to do them.

spiritus

AdrianC said:

Only doing 3k in the last year certainly won't help one tiny bit...

Can you see the discs through the wheels? If so, what did they look like?

The car is now in the garage awaiting it's MOT. I'm waiting on a second quote for the discs. I'm presuming MB are including pads in that price??

spiritus

I asked MB if the car could fail it's MOT due to corroded discs and they said that potentially yes

MinuteNoodles

It's a con. "Rusty brake discs" is one of the easiest money making scams there is because all brake discs get surface rust on the parts that the pads dont clean and they can point at a bit of surface rust and go "that's rusty, they need replacing" when in fact there's nothing wrong with them. Surface rust on the centre hub and outside edge is normal. Even this is normal, perfectly safe and will pass a MOT as long as there's not too much of a lip between the shiny bit and the rusty outside bit:



When it's not normal and you have a problem is when there's heavy rust on the area the pads are in contact with. Even light surface rust isn't an issue in this area if the car has been stood a while as a few miles of driving around town will see the brake pads remove that. It's only when it's like the following picture you've got issues and you won't get that on anything less than half a decade old unless it's been stood unused that entire time.

I'm betting it'll pass it's MOT fine if it's not being tested at the same dealership who told you they needed replacing. If it passes don't waste your money. If it fails get a second opinion. Brake discs on a 3 year old car at 16k should only need replacing if you drive the thing like Lewis Hamilton and even then only because the discs have worn thin from super heavy use, not because of any rusting.

MinuteNoodles

The_Rainmaker said:

Rear discs always need replaced sooner because the braking is weighted towards the front wheels and the back discs corrode more.  When I had a 230E the rear discs were replaced every second year. I wouldn't be paying a main dealer to do them.

Utter poppycock. The rear discs on every car I've had in the last decade and a half have lasted much longer than the fronts. My last car I bought at 38k and sold at 155k only had two sets of rear discs on in that entire 155k, being changed around the 70,000 mile mark each time. The previous car I bought at 3 years old with 90k on and sold at 8 years old with 168k on only had one set in my ownership.

If you were replacing the rears every 2 years either you had a problem or someone was taking you for a ride.

tacpot12

I think the wear rates will be  heavily influenced by driving style; a slow driver doing a few short journey's might will find that the rear disks suffer with corrosion because they are basically never used; they rot rather than wear out. A fast driver doing lots of long journeys involving heavy braking will go through the front discs more quickly that the back. 

The dealer says the discs are scored. If this is correct, you will be able to feel the ridges in the discs, and new pads should be fitted to new discs. The old pads might have lots of meat left on them, but the will have conformed to the shape of the ridges and if fitted back on when new discs are fitted, suddenly you will much less effective brakes until the ridges have worn off the pads. The pads are so cheap that you might as well fit new.   

daveyjp

MinuteNoodles said:

It's a con. "Rusty brake discs" is one of the easiest money making scams there is because all brake discs get surface rust on the parts that the pads dont clean and they can point at a bit of surface rust and go "that's rusty, they need replacing" when in fact there's nothing wrong with them. Surface rust on the centre hub and outside edge is normal. Even this is normal, perfectly safe and will pass a MOT as long as there's not too much of a lip between the shiny bit and the rusty outside bit:



When it's not normal and you have a problem is when there's heavy rust on the area the pads are in contact with. Even light surface rust isn't an issue in this area if the car has been stood a while as a few miles of driving around town will see the brake pads remove that. It's only when it's like the following picture you've got issues and you won't get that on anything less than half a decade old unless it's been stood unused that entire time.

I'm betting it'll pass it's MOT fine if it's not being tested at the same dealership who told you they needed replacing. If it passes don't waste your money. If it fails get a second opinion. Brake discs on a 3 year old car at 16k should only need replacing if you drive the thing like Lewis Hamilton and even then only because the discs have worn thin from super heavy use, not because of any rusting.

Neither of those are vented discs.  It is possible to have a brake which looks like the first photo, but the vents are rusted away.  I've seen it on an Aygo. 

An extreme example.

https://www.bobistheoilguy.com/forums/threads/rust-on-brake-rotors-when-is-it-a-problem-picture.295650/#post-4857870

MinuteNoodles

Where have they rusted away? That's dirt that builds up on them and goes hard and gets a rust colour because of the surface rusting of that edge of the disc. Some of the comments in that thread are even:

"I think it looks a lot worse than it is because of the scale, I'll bet if you knocked it off it would look fine. Par for the course on a rustbelt commuter car, "

"5 year old rotors up here can look like that thanks to all the salt in the winter and they are fine other than cosmetically unappealing."

And that's my experience from working in main dealerships including a Land Rover dealership many years ago. Once upon a time during a service it was common practice to get a hammer and chip all of that crud off and give the ribs a quick go over with a wire brush. You'd then end up with a nice flat pretty looking surface that looked like it should, albeit a dark brown coloured one. It would appear that that practice, along with things like greasing door and bonnet/boot hinges, check straps and latches has died the death and for people like you who have never cleaned the crud off the disks you automatically assume it's actual rusting metal from the disc coming off when it isnt at all. But then again if you clean up the crud off the discs you can't convince someone perfectly servicable discs need replacing because they're rusty.