The factory rotor set screws are easily damaged during removal and by the excessive heat and elements that they’re exposed to on a daily basis. If the screws on your rotors are corroded or damaged, replace them to make your next brake job a bit easier. These stainless steel screws will not rust, and can be used again and again when changing your rotors.

Plan ahead. Install stainless screws on this brake job, and you won't have to drill them out on the next one.

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What material is the rotor? Will the dissimilar SS screw cause corrosion of the rotor instead?

 

The factory rotors are cast iron, and have a coating on the hats to prevent corrosion. There should be no issue with dissimilar metal bonding between the screw and the rotor. The main area of concern is between the screw and the iron hub. 304 stainless steel is deemed suitable for this application, and is preferable to the stock zinc plated screws. Since the area of the less noble material (the iron hub) is very large compared to that of the more noble material (the 304 stainless screw), the galvanic corrosive effect is greatly reduced, and in our experience and testing has proven to be negligible. With the application of anti-sieze on the threads, the hub and screw are electrically insulated and this already minimal corrosive effect is virtually eliminated.

With the stock zinc plated steel fastener in iron hub:
The corrosion of the base metal is not increased by the fastener, however the plating on the fastener is rapidly consumed, leaving the bare fastener metal - This eventually leads to a seized fastener, bonded to the hub due to rust. This is what we're trying to avoid by using a stainless fastener.

304 stainless screw in iron hub:
The corrosion of the base metal is only marginally increased by the fastener, and the rate of corrosion is greatly reduced compared to the stock bolt. In this application, this corrosion effect is deemed negligible due to favorable anode/cathode area ratio and the easily insulated materials through use of a lubricant (such as grease or anti-seize).

If you have any other questions or concerns fell free to ask me and I will gladly get an answer for you as soon as I can.

 

Regardless of the size of the hub, the corrosion will happen where the contact is made. If anti-seize were electrically insulated there wouldn't be an issue either way, stainless or not. Anti-seize is NOT going to be electrically insulating the two. I'd bet if you liberally applied anti-seize, you'd not even have a .1 ohm resistance between the two. It would be super easy to test with a ohm meter. However the anti-seize will protect the surface somewhat where it is in contact on either screw material and this will help.

If the screws are stainless, corrosion of the base metal would be increased by the fastener located right around the fastener as anyone with a boat would be able to tell you from experience. It doesn't matter how big the hub is.

You acknowledge the corrosion of base material with SS screw here. Of course the corrosion of the screw would be greatly reduced because the corrosion transfers to the hub instead.

I wonder if material such as CorrosionX (which I use on my boat) or other would be good in either situation? How hot the rotors get would be a factor as of course are the location, salty roads, etc.

Don't get me wrong, regardless of hub material, I would prefer SS screws however I would use a corrosion resistant material on them as well as a touch of anti-seize. I would have to make it a point to inspect the area around the screws regularly to check for corrosion. Once it starts, it seemingly goes exponentially.

 

For galvanic corrosion to occur you have to have extremely good contact between the two metals. There must be a conductive path for the metal ions to move from the more anodic metal to the more cathodic metal. Anti-seize will interrupt this process enough that the small electrical potential difference between our two metals is unlikely to produce corrosion under any normal circumstance.

This is not entirely true. A large area of noble metal in contact with a small area of less noble will accelerate the galvanic corrosion rate. It is common practice to fasten aluminum sheets, which is even more anodic than our cast iron hub and rotor, with stainless steel screws, but aluminum screws in a large area of stainless steel are likely to rapidly corrode.

Corrosion is unlikely to occur at all with our stainless screw. The point we are trying to make is that if it does occur, it will be on the hub, and not the screw, which is definitely the preferable outcome.

Temperature, humidity and salt exposure can all affect the chances of corrosion, but our screws should be safe even in very harsh driving conditions, including the excessive amounts of salt they use on the roads here in Ohio. If you use your Cayenne to launch your boat, I can see your concern over corrosion. I have no personal experience with CorrosionX so I can't help in that regard, but regular inspections will help a lot.