[voxmagna]

I was surprised when I had to replace both ventilated front brake rotors at 41K miles on MY07Tdi. Sport. I don't do many annual miles and have done 10K on the replacement aftermarket rotors in a couple of years. MOT 'advise' said rotors are pitting, but not a reason for poor brakes or failure.

I've always thought the VW pads I've changed were very hard and full of metal (?). Any ideas from the metallurgists on whether pitting and rusting of rotors with standing a lot is due to the metal composition of the rotor itself or the type of pads? Since I'm hardly doing any miles I wouldn't expect the pads to be the problem but they are in close contact with the rotor all the time and I thought HR pads had metal (steel) in them. The Metal Frein pads I used to buy years ago had brass not steel in them.

 

[silvershadow]

The reason the rotors wear instead of the pads is simple - the rotors are hard and the pads are soft in relative terms.

Any abrasive material that gets in between the rotor and the pad will imbed in the softer pad material and then act like sand paper on the harder metal disc -the hardest of "hard" pads are still significantly softer than the metal used to make disc brake rotors.

Tribology Rule #101 in every day language from a long-time metallurgist..............

 

[voxmagna]

It's the rust/corrosion/pitting issue I was trying to understand, although it seems to be something everybody puts up with on cars that do low mileage and stand a lot. It is also responsible for shorter pad life because when the car does get used the pads are grinding off the rust and pits. I am very light on brakes and use engine braking a lot which adds to the problem.

The only solution I read was carbon fiber rotors, but they would cost twice the value of the car! Where I was heading was to find out if rotors are sold with different metallurgy - not just for wear life but corrosion. Pay a bit more and get more chromium? Locheed rotors are sold with a plating but this won't help on the pad contact area. Next rotor change I might go to a well known brand where quality may be better.

 

[silvershadow]

Vox,

I have lost touch with brake rotor material selection including the high-tech materials used on high-performance and racing cars. As far as I am aware most production cars still use the traditional cast-iron due to its thermal mass and conductivity for cooling efficiency - cooling between use is critical for minimising brake fade problems.

I have never regarded corrosion resistance as a key selection as 90+% of cars are frequently driven meaning there is little time for corrosion to occur. Of course cars that are infrequently used will be more prone to corrosion. Most brake callipers are designed for quick pad changes and the cost of replacement pads is reasonable compared to other maintenance expenses.

High-tech braking systems are for high-tech cars with costs to match - the answer to your concern rests in your wallet......................

 

[voxmagna]

I've not found a solution even though many low mileage drivers complain of the same problem. When I do drive the car I'll just have to do some mileage with my foot on the brake more. It means the pads and rotors will still have the same life. Some suggest putting tire covers over the wheels, but I can't see that working. One thing I might look at is whether parking the front over plastic sheet changes things. I remember a company car that was always parked over grass and the under body rusted out after 3-4 years.

 

[Shadow_Rusty]

A wheel cover may stop rain splashing onto the rotors...
Not sure if that will actually reduce the rusting, although, it may just be more consistent, instead of pitting.

 

[mickjane2]

I also believe the driving style can affect brake disc/rotor wear. I have found that those who tend to drive more sedately with gentle braking tend to suffer more disc corrosion than those who tend to brake much harder, the latter tend to go through more pads IMHO.

****

 

[voxmagna]

That's me then.