Paint these Calipers? Are these coated or bare cast?

[SolarPoweredPickles]

Hey VW peple!

I expected these rear disc calipers to come in the ol' grayish cast color. Sort of a gold broze, Are these coated or bare material that will rust? I can't tell if I should paint them or not, I dont mind the color they are similar to my fronts that came painted and look fairly similar, so I wont paint unless needed, but these im unsure.

Thanks

[scrivyscriv]

It looks like Alodine but I'm almost sure the casting there is ferrous, which rules Alodine out. It has some kind of surface treatment that appears to be electroless plated, if I had to just guess. It will corrode over time. But not as fast as bare metal.
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Robert in Memphis
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If you're ever in the Memphis area, you are welcome to stop by for advice and help.

[raygreenwood]

Those are cast iron (some calipers "might" be cast steel).

They are zinc plated and have a top chromate passivating coat (that greenish gold color).

The zinc plate of course is a sacrificial anode to prevent the steel/iron from rusting. The zinc lasts for years preventing rust.
But....they call zinca "sacrificial" qnode because the zinc slowly degrades into a whitish powder (called white rust). Eventually, maybe 7-10 years down the line the zinc is depleted and the steel/iron underneaty will start to rust. This process of zinc degrading literally starts the second the plated part comes out of the plating vat and hits air.

The gold chromate.....is a sacrificial anode to protect the zinc. After zinc plating the part is dipped in a chromate solution that can either be clear or impart a color like gold, red, yellow, green or blue. Think of it like an activated sealer. It prevents oxygen from reaching the zinc and causing it to begin its sacrificial degradation process.

So, with zinc you might be rust free in ferrous metal for anywhere from 5-10 years. With zinc sealed with a chromate you might double that amount of rust free time.

Years ago most of these were top coated with an iridescent gold color that most just called "zinc chromate". The chromate portion was hexavalent chrome (chrome 6).....very nasty. Deadly stuff. A lot of it is now done with Trivalent chrome (chrome 3)....not deadly but you would not want to eat it or wear it. It has a little less top coat life than chrome 6.

In short.....no. Don't paint them. It won't hurt them though. If you decide to paint them them...VHT caliper paint is awesome stuff.

Ray