Cupra 290 rear discs corrosion?

[missmouse]

My 2019 Cupra 290 rear discs are getting a lot of corrosion. Ive done a few hard stops from high speed lately but not had a lot of effect.
Olden days you could drive about with the handbrake on very lightly but with electric h/b its on full or off!
Guess Ill need to take them off & clean them properly before the rust gets embedded?
Discs have already been replaced by last owner under warranty!
Anyone else get this problem?

 

[cairus]

is a known problem in the group.

 

[Mr Pig]

Rear disks don't work very hard so it's not unusual for them to rust. It doesn't make much difference what the brand is, they're just lumps of cast iron. You can't clean them with breaking as the corrosion is harder than the pad material.

You could have the disks skimmed. Used to be a common thing but you don't hear of many places doing it these days. Personally, I'd just replace them. New rear disks and pads isn't crazy expensive and it's the best solution.

There isn't a lot you can do to stop it. It's mainly down to the kind of driving you do. My car is not too bad but my wife does less miles and mostly around town and her rear disks are knackered. They'll be getting replaced soon.

 

[Mo_86]

My 2019 Cupra 290 rear discs are getting a lot of corrosion. Ive done a few hard stops from high speed lately but not had a lot of effect.
Olden days you could drive about with the handbrake on very lightly but with electric h/b its on full or off!
Guess Ill need to take them off & clean them properly before the rust gets embedded?
Discs have already been replaced by last owner under warranty!
Anyone else get this problem?

Have you got any pictures of how bad they are before and after a drive.
Mine isn't a cupra but if my car has sat for more than a day in rain they do get yellow which goes very quickly after a short a to b drive.

 

[SuperV8]

As above, lack of use is the usual culprit.
If you are not using the car daily, rust will build up over time. Brake discs are just grey cast iron.
It's made worse by the fact the Cupra is over braked (for 155mph speeds) and has large and vented discs all round (high heat capacity), so just putting about they will be even harder to get heat into them.

To keep your discs nice and shiny you need to use your brakes, at least once a week do some higher speed, heavier/repeated braking - the kind of braking which would make your passenger 'uneasy' so best to do it solo and obviously with no one driving behind you!
Once a week I usually leave my braking upto a few large roundabouts a bit late, so 70 down to 10 - which is also down a hill.

 

[PaulusB]

I replaced them with Zimmermann Coat z rotors no rust anymore.

 

[Mr Pig]

To keep your discs nice and shiny you need to use your brakes, at least once a week do some higher speed, heavier/repeated braking - the kind of braking which would make your passenger 'uneasy' so best to do it solo and obviously with no one driving behind you!

I don't think you need to be that aggressive. Normal breaking coming off a motorway, in fact normal breaking during higher speed driving in general. Most cars don't suffer this issue. The killers are little use and predominantly low-speed/town driving. You need to get the rust off while it's just light surface rust. Once it's into the metal no amount of breaking will remove it.

 

[SuperV8]

Rear disks don't work very hard so it's not unusual for them to rust.

On resent brake testing we were seeing over 700 degrees C on the rear axle brake vs 500 on the front axle brake (VW Passat) - so yes the rear brakes are working hard!
True - The rear axle usually has less braking force due to weight transfer - but they are downsized accordingly so still see high temps/work hard.

 

[Mr Pig]

On resent brake testing we were seeing over 700 degrees C on the rear axle brake vs 500 on the front axle brake (VW Passat) - so yes the rear brakes are working hard!

The fronts are vented and that will not be on city driving.

 

[RUM4MO]

The rear discs on the car the OP was are also vented.

The sort of corrosion/roughness etc I see on my older daughter's May 2019 Leon Cupra even from an early age - maybe from 3 years old, are well past the stage where serious braking would do much, really just something has not been thought out and/or tested when that rear end braking system was thrown together.

Edit:- and, at the 4th annual service, I replaced the rear pads with the correct genuine VAG product, but that was only done to make sure that the friction material was kept at an acceptable(to me) thickness. Next move will be to replace the discs and pads as I'd doubt if these discs, in their present condition will now be causing high wear of the pads.

 

[SuperV8]

The fronts are vented and that will not be on city driving.

I was responding to your comment " rear brakes don't work very hard" - they do, on all cars since the adoption of brake force distribution.

Some of the more severe testing is repeated 50 to zero tests (city driving can be severe), as you have less cooling time between each stop. The lower decel stops also mean there is less weight transfer and the rear axle can proportionally do more work.

 

[Mr Pig]

I was responding to your comment " rear brakes don't work very hard" - they do, on all cars since the adoption of brake force distribution.

Brake force distribution has been around for a long but it's still not unusual to see cars with rusty back brakes while the front disks are fine. Bottom line is that if you don't do enough of the right kind of miles your disks will rust and, for whatever reason, it's always the back ones that go first.

 

[DEAN0]

If the load proportioning system works as it should - a few bags of sand ( or similar ) in the boot of the car for a week or so should have the rear brakes doing a bit more work and help to clean up the discs.

 

[Mr Pig]

If the load proportioning system works as it should - a few bags of sand ( or similar ) in the boot of the car for a week or so should have the rear brakes doing a bit more work and help to clean up the discs.

Innovative solution!

 

[Mo_86]

Still not seen a pic of the rear brakes to see how bad they are.
I would check whether the rear brakes are even activating.
Go for a drive and see if theres much heat coming off it.
Here's my rear discs, they are just over 2 yrs old and i do around 5k a yr, mainly a to b with very little spirited driving and no rust issues.
There is scoring but other than that they're fine.