Why do brake discs rust?

ruster — New brakes – expensive and beautiful

Change brake discs at 50 km? The family's hybrid car was submitted for its very first EU inspection at Møller Car Oslo West. Shortly after, the result came. Two 2's. More than 25% rust on the brake discs - front and rear.

Is it our fault?

The problem is well known. The brakes must be used, otherwise they will rust. The workshops are quick to point this out. You should know that this is solely your own fault. Several people have experienced getting the same message. There is well-intentioned advice on the web about repeated braking from 80 km/h. One piece of advice is to end each drive with a strong brake so that you always park the car with dry brakes.

Is it only the which is needed?

My wife, who drives the hybrid car the most, brakes more often than I do. Not strong braking from 80 km/h, but significant stops in front of the traffic lights. The hybrid car switches to electric operation when you let off the gas. Then the 1,5-ton car rolls freely without any engine brake and must be braked with the pedal. My wife never uses "artificial engine braking". The point is that our hybrid car brakes at least as hard and as often as the previous eight new cars we have owned since the Periodic Vehicle Inspection (PKK) was introduced in 1998. We have never had to change the brake discs on them.

A growing problem

Several people experience having to change brake discs after a short time due to rust on the brake discs and complain about their distress on online forum sites. The explanations seem obvious. Battery-powered cars are responsible for the increase. Since these cars can recover braking energy via the power system, you don't have to use the ordinary brakes as often. What is often referred to as an "artificial engine brake" is a dynamo, with controllable resistance, - following the same principle as bicycle dynamos of old, which were tilted onto the tire to generate electricity. Cars with e-pedal can be driven for days without using the brake pedal.

Not only battery cars are affected

I have searched through newer cars for sale at Finn.no to investigate whether battery-powered cars report changing brakes to a greater extent than pure petrol and diesel cars. I immediately find that cars that can be driven with one pedal, such as the BMW i3 and Nissan Leaf, are well represented. When I compare models that come with both hybrid and petrol/diesel – for example the Audi A3 and BMW 3 Series – I see no significant difference. Both types seem to be equally hard hit. When I looked more closely at the individual ads, I found that some cars with only petrol/diesel drivetrains had had the discs changed due to wear and tear - no rust. Not unexpectedly, diesel cars have a higher mileage than corresponding battery cars.

Too soft steel?

With a focus on "wear and tear damage", I see that a striking number of car owners in Europe have had to change brake discs far too early due to wear and tear, – not rust. well, inner calm amplifier wear and tear - and vice versa. The soft steel in the discs can easily be damaged. I fixate on one trait that several car owners from, among others, the Volkswagen group experience: Brake discs full of deep, dark furrows. They seem to have been out in really bad weather - or bad blocks, despite the fact that they are almost new cars. The workshops explain the abnormal wear by saying that the brakes have been used too little and are therefore exposed to dirt. Either way, they will be very susceptible to rust attack.

Already after the first winter, the discs on our car looked the same. Not just at the back - but on all 4 wheels. Repeated attempts to brake hard produced no visible improvement. I have never seen brake discs become so deformed in such a short time. The steel in the discs appeared to be very soft - almost self-destructive - like a Japanese car from the 70s. I have read that the quality of discs can vary from batch to batch. The problems are not discovered until they are put into use. The question is whether the new original brake discs are as bad as the factory fitted ones.

No surprise

The Volkswagen Group's hybrid cars have annual service intervals. At the first service, I feared that all four brake discs would have to be replaced - not because of rust, but because of abnormal wear. It didn't happen. Not the following year, either. I have seen pictures of discs that look just as bad and were replaced after a year. Why weren't we advised to change discs earlier? Was it for fear of triggering an avalanche of warranty claims from customers? When the discs look like a freshly plowed field, it is difficult to avoid rust attack. For Møller Car this course is very favorable. Rusted discs must undoubtedly be replaced - at the car owner's expense. It is not as easy to defend that car owners have to pay to change brake discs after only 6 months due to abnormally high wear. The strategy is smart.

Wait for the rust to arrive, then the customer will have to pick up the bill.

No guarantee

Brake discs are considered a wear part that you are not entitled to have covered by the car's new car warranty - neither in this country nor elsewhere. This has been read and adopted. Some car brands still covers abnormal wear and tear, but you are therefore not entitled to this. It is pure goodwill.

Advice against rust on the brake discs

Leasing/trade-in
When you hand in the car after the end of the lease or exchange it for sale, you will be charged for everything that is not considered normal wear and tear. Here, bad brake discs have started to become more and more common. Several leasing customers have received an additional bill after they have delivered the car. If there is more than 25% rust on the discs, the leasing company can require them to be replaced at your expense. Please note that even professional mechanics can have problems assessing the degree of rust on the brake discs. It may therefore be worthwhile to obtain an independent assessment before the car is returned.

Use the brakes!
The best advice against rust on the brake discs is to brake hard a few times on the country road. This is not as easy if you live in a city. Find a good, fixed "braking place", for example when turning off the main road. Give the signal early - and if you don't have a car right up 'in the trunk', you can hit the brakes well before turning. Since the rear brakes are more prone to rust, it can be smart to slow down with the handbrake if you have a mechanical breakdown. But remember that the brake lights do not light up when you use the handbrake. Electromechanical hand brakes don't work at speed - they just engage and disengage.

Flush the brakes often in winter!
If you have access to a high-pressure washer/self-washer, you should take care to flush the brakes through the rim. Be careful not to direct the beam on the inside of the wheel as this can damage the rubber cuffs.

Ask for cleaning/lubrication of the brakes at service!
This can be smart to carry out every other year - especially on the rear brakes. It is also necessary if you are going to preserve a vehicle for the winter. We have previously paid between NOK 700-1000 for this for one pair of wheels. Here you do not need to use a branded workshop. If you have experience in changing brake discs, you can also carry out the job yourself. There are tutorials on Youtube.

Look for abnormalities!
Even if you have a new car - or just new brake discs, it can pay to monitor how they wear. Feel free to take pictures so you can catch signs of damage as early as possible. They can already appear during the first winter months.

Quality can be very inconsistent from batch to batch and even from one rotor to the next... There are many different grades of cast iron, and some make much better brake rotors than others. – Knowyourparts.com

It is not only the cars from the Volkswagen group that have bad metal in the brake discs. Honda Jazz has for many years been a winner of the TÜV tests in Germany and Austria. But from 2008, the status has fallen. According to TÜV, this is solely due to bad brake discs, and here the blame lies with manufacturer, not the consumers (Zeit Online).