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996 disk rust

johnny

Monza
Joined
11 Feb 2003
Messages
229
Been away for a while only to take out my pride and joy to find that she has been suffering from a known 996 problem of rusting disks.

Anyone know why they are so prone to this or anyway of preventing it, other than the regular use.




Migration info. Legacy thread was 12772
 
It happens to absolutely EVERY car. Some hard braking will get rid of it.

Migration info. Legacy thread was 12780
 
It happens even after an overnight in the garage. OPC advised me to try to garage only when the disks are as dry as possible.If wet I usually drive up and down the road, brake heavily a few times then straight into the garage.Park in gear with the handbrake off.........and the disks are still rusty and bind the next morning !

Migration info. Legacy thread was 12788
 
Why don't they make disc with stainless steel? 'cos sometimes my brakes ceases after a few wet days, and it takes quite a jolt to ease it off. Can't be doing the pads much good. Is it because s. steel doesn't have the same friction coefficiency or something like that? I don't think cost is the problem because if you use the car not too often, you won't need to change disc that often anyway, but if you have to wear off a layer of rust every time you take your car out, the discs won't last that long I'm sure.

Migration info. Legacy thread was 12799
 
As far as I know they don't make brake discs out of stainless steel due to the cost of manufacturing - normal steel discs are cast into shape (i.e. molten metal is poured into a mould) and the braking surfaces machined flat (which is why they are brittle). It is not possible to cast stainless steel in the same way, they would have to be machined out of a solid lump which would be much more expensive.

Migration info. Legacy thread was 12809
 
People make stainless steel exhaust and pay huge amount of money for it, why can't someone somewhere make stainless disc? OK, you'll have to change it evntually unlike exhaust, but for people who don't drive the car very often, surely it's worth the extra cost! Otherwise everytime you use the car you "waste" a mm or so off the disc!

Migration info. Legacy thread was 12867
 
Stainless steel exhausts are made out of sheet metal, the same as mild steel exhausts, so the manufacture methods are basically the same for both. Obviously stainless steel sheet costs more than mild steel, and stainless is harder to weld, but the manufacturing costs are similar. I think the sheet metal/raw materials only counts for something like 10% of the cost of an exhaust.

To machine a disc out of stainless steel would cost a fortune, even more than the ceramic discs (which are pressed into shape at high temp and pressure) used on latest Porsches. Basically the material cost would become insignificant.

If you wasted a mm off the disc every time you used it, it would only last a week. You will only lose a fraction of a mm each time. It sounds/looks worse than it is. Cast steel discs are so much cheaper than any alternative they are the only economical option, even if you changed them every year.


Migration info. Legacy thread was 12871
 
of course, the Porsche ceramic composite brakes don't have this problem ;)

Or the Brembo carbon fibre discs

So there are alternatives


Migration info. Legacy thread was 12875
 
The cermanic brakes seem to have been a complete disaster, although nothing official has been said. Owners, however, have found they crack under normal track use and need throwing away every couple of months!!! From what I have heard they are totally useless - owners who track their 996 Turbos that are fitted with ceramic brakes take them off for track work and fit steel brakes which seem to be much more resiliant to repeated, hard braking.

Migration info. Legacy thread was 12876
 
Aren't F1/racing brakes carbon? I guess they work well in high temp and only last a race.

Migration info. Legacy thread was 12900
 
The Porsche ones are ceramic rather than carbon - perhaps carbon discs are more robust or, as you say, they just need to last one race!


Migration info. Legacy thread was 12905
 
Yes, F1 brakes are carbon, and they do only last one race. The biggest problem with carbon brakes for road cars is that they need to get up to temperature before they work properly, so would be dangerous. F1 drivers left foot brake constantly around the warm up lap!!

Carbon brakes were first developed for aircraft.

Ceramic brakes work better from cold, but I am not surprised by what James says as they will be a lot more brittle than metal discs. The only advantage of the ceramic braes is that they can operate at higher temperatures (oh, and they don't rust :wink: )




Migration info. Legacy thread was 12906
 
....and they are slower-wearing and considerably lighter. Too bad they haven't got them quite right yet

Migration info. Legacy thread was 12911
 

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