Do these brake discs need replacing

[mawallace]

Took my car for an MOT at the local dealer. they made a number of advisories, one of which was my rear discs which were 'showing signs of corrosion'.

I asked for proof and where given these pictures. They said they were 85% worn.

There's no sign of juddering.

The car has done 59,000 miles - they are the original.

I was wondering how often they should be changed.

Thoughts please?

[TooMany2cvs]

mawallace said:

Took my car for an MOT at the local dealer. they made a number of advisories, one of which was my rear discs which were 'showing signs of corrosion'.

I asked for proof and where given these pictures. They said they were 85% worn.

There's no sign of juddering.

The car has done 59,000 miles - they are the original.

I was wondering how often they should be changed.

Thoughts please?

They're certainly scaggy.

"85% worn"... What's the minimum thickness, and what're they down to? Pads?

If t'were me, I'd be seeing if those rear calipers were a bit sticky, too, because it doesn't look like the entire disc swept area's in use. 59k in how many years? This the first MOT?

[GreenV8S]

mawallace said:

I was wondering how often they should be changed.

When they need it. Which was several years ago judging by those pictures. Why isn't the pad bearing on the outer section?

[Sheepshanks]

GreenV8S said:

Why isn't the pad bearing on the outer section?

Rust wears the pad away so it never bears on the disc itself. They'll probably look worse on the inside faces.

Unless you're driving pretty hard I find rear discs generally end up looking like that - fronts can too on very gently driven cars, especially if the car isn't used every day so the rust gets chance to set in.

It's not helped by brakes not being serviced these days - years ago it would be standard practice to strip and clean them every year. Now they don't even get a spray of brake cleaner.

[stevensdrs]

You would normally change the discs every second set of pads or earlier if at the minimum thickness.

[mawallace]

Thanks for the replies. The car is 4 years old,done 60000 miles.

I now do approx 16000 miles a year

[Mignon]

Disks are fine. All disks get rusty. Nothing to worry about. If they really needed changing it would have been a fail not an advisory.

[Pericoloso]

Mignon said:

. All disks get rusty..

No they don't.
I'm pretty flippant on advisories but I would change those pictured if it was my car.
Certainly wouldn't send it for next MOT with those.

[GreenV8S]

Sheepshanks said:

Rust wears the pad away so it never bears on the disc itself. They'll probably look worse on the inside faces.

I don't recall ever seeing the pad itself rusting - only the disc. I can't see why the rust would be so much greater on the outer section of the disc. One possible reason is that the pads have worn tapered because they are used in single sided calipers with a worn slider - but I don't know if that's the cause here. Whatever the reason, that brake isn't working as designed and imo needs attention.

[helix402]

You need new rear pads and discs.

[Sheepshanks]

GreenV8S said:

I don't recall ever seeing the pad itself rusting - only the disc. I can't see why the rust would be so much greater on the outer section of the disc. One possible reason is that the pads have worn tapered because they are used in single sided calipers with a worn slider - but I don't know if that's the cause here. Whatever the reason, that brake isn't working as designed and imo needs attention.

They go rusty on the outer edge and it creeps across the face of the disc - exaclty as it has done in the picture - as it does this it rubs the pad away. It's quite common to end up with a narrow shiny band and the rest of the disc rusty.

[227bhp]

Yes they need changing along with the pads and the calipers/slides need checking and greasing, you got your moneys worth out of them at 60k and they usually aren't expensive.
Rusty discs are not an MOT fail if they still work ok on the brake test, but that doesn't mean they aren't sub-optimal.

If a safety tester flags it up as concern then do it, that's what they are there for. It certainly won't get better, only worse, so you'll have to change them sometime.

[Higgs boson]

I'd spend a couple of quid on a wire brush.

[Evolved]

Replace those and the pads. Hardly bank breaking stuff.

[RichB]

Sheepshanks said:

They go rusty on the outer edge and it creeps across the face of the disc - exaclty as it has done in the picture...

Surely a spray of WD40 on the discs should prevent any further rusting.

[227bhp]

RichB said:

Sheepshanks said:

They go rusty on the outer edge and it creeps across the face of the disc - exaclty as it has done in the picture...

Surely a spray of WD40 on the discs should prevent any further rusting.

Just go all the way and smear some grease on too.

[Evolved]

227bhp said:

RichB said:

Sheepshanks said:

They go rusty on the outer edge and it creeps across the face of the disc - exaclty as it has done in the picture...

Surely a spray of WD40 on the discs should prevent any further rusting.

Just go all the way and smear some grease on too.

WD40 to stop rusting brake disks, where has this info come from?

[E-bmw]

Yes, they need replacing before they get worse, let's face it they aren't going to get any better.

[38911]

Nothing at all wrong with them.. do a few full on emergency stops from high speed (80mph+) and the rust will magically vanish and they will look like new.

[stevieturbo]

If the visible side is like that, you can be sure the other side is a lot worse.

Discs/pads are dirt cheap, there is no excuse for having brakes in a poor condition and as others have said could also be indicative of sticky calipers.

Just change them. And as for what any MOT test might reveal...it's a quick and basic test and many testers tend to ignore a lot of stuff.

if a proper brake test has been carried out, what did the sheet say about side/side balance of brake performance ?