What do we think of the rust on the outer edge of my rear disc? I have my thoughts, but am interested to see what others think.

The photo is from the 310mm N/S rear disc on my 2020 vRS 245. The O/S rear disc looks the same, with a narrow band of rust on the outer and inner edge of the braking surface. The front are absolutely fine, with plenty of pad material left and no lip.

The caliper in the photo is brand new, fitted in July. The other side was new last year. I replaced the discs and pads all round last August, with OE VW parts.

The car has covered around 10k since the brakes were fitted. There is no lip on either rear disc, and the pads seem to have plenty of meat on them - although being the rear they are quite difficult to see properly. Certainly, the edge of the pad I can see clearly (the inner edge of the disc) is nice and square with the edge of the braking surface. Both pads do have some rust on the edges, but that'll be from where the handbrake was applied after it was washed.

The condition of the brakes can be seen by the hub/bell and the vents - they aren't even remotely worn (shields aside!).

The disc rusted over following a wash last weekend, and the car has only been to town (20mph zone) since then. It did however get a decentish run in some NSL country roads this evening, with some steep hills, which I'm suprised hasn't cleared it up.

I think it's just one of those things- and it is minor. That said, I'm posting here as I've never really seen this before when the discs and pads are in good condition, and I thought the run tonight would have sorted this.

Any ideas?

I think that's not meant to be malicious, you're thinking too much

Agreed, this is normal

+1 on 'normal'. I switched to VBT discs after the the rim on both front and rear brakes got too much, but that was after 5+ years' daily use.

Quite normal, no problem. Any rust on the faces will burn off at the next application.

My 1990 Audi 90 20v used to eat vented front brake discs as a light snack when I ran it as my company car, changed at every other service at around 20,000 miles while the pads lasted around 2 1/2 discs..... I did use Greenstuff pads though for less black dust and better intitial bite.

So, an update a week later -

There's been no change. Okay, the car hasn't been driven much, but it's still a bit weird.

I guess I'll just keep an eye on it. It stops fine with no noise, and the handbrake operation is perfectly fine too - who knows.

I've only ever seen this on cars with worn out brakes, hence why I'm still questioning it!

Not really sure what you are worried about.

On 22/09/2025 at 09:29, OccyVRS said:

What do we think of the rust on the outer edge of my rear disc?

The rust is just where the pad doesn't touch the rotors.

It's just steel, it will rust. The whole lot rusts, but the pad wears the rust away in the part where it contacts the rotor.

1 hour ago, OccyVRS said:

There's been no change.

Why would you expect to see a change?

It's not like your pad has increased its contact area.

1 hour ago, OccyVRS said:

I've only ever seen this on cars with worn out brakes,

The wear on the disk is nothing to do with the rust.

Brand new rotors will rust in the shop if they weren't coated in light oil

Some people dont have logical thinking do they. If the pad doesnt rub in that area of the disc it wont make it shiny. Obviously didnt look at it when it was new and whole disc was rusty from the sea trip. Mine were not only rusty but had grooves as well Wore out in a short time. Dealer said "Perfectly normal"

I'm fully aware that the pad doesn't cover the entire braking surface of the disc. The reason I'm interested in it is that I see no reason why it would suddenly start showing up now.

@Exkiwi you love brandishing your sweeping statements. Logically -

1) The pad doesn't cover the entire braking surface of the disc

2) The pad has never covered the entire braking surface of the disc

3) The front brakes are fine, and the O/S rear is largely fine, so why is it only the N/S rear?

I'm completely aware that there is nothing wrong with the brakes - I'm just curious. Why, up until this point has the entire disc been cleared of rust after braking, yet suddenly it's not?

Maybe I should cure the problem by springing for carbon ceramics...

@BlueWagon by worn, I meant pads with uneven wear, down to the backing, with contamination, etc.

3 hours ago, OccyVRS said:

, so why is it only the N/S rear?

Maybe it gets exposed to more weather or moisture than the others. Eg parking conditions, water thrown up by front wheels

5 hours ago, OccyVRS said:

Maybe I should cure the problem by springing for carbon ceramics...

In my experience it will unfortunately not solve the problem

Either way, it's now a secondary issue. I've been underneath the car, and seen that the passenger side CV boot is absolutely knackered - grease slung over everything.

I'm hoping the joint is fine - don't see why not, but I'm also not sure how long it's been oozing lifeblood out.