Rust on caliper

[Brian Cembor]

Okay, first off I think you are confusing surface rust with rust through. If
the object in question is thoroughly rusted it will, more than likely, be
brittle as rust actually changes the physical properties of the material.
The mounting knuckle is steel, I believe, and the through bolt is alloy,
both less likely to rust through. Take a steel wool pad and some WD-40 or
other lubricant/solvent and try to see if it comes off the caliper. Be sure
to clean all this off before diving the car as a slick caliper is not really
that safe. The parts that make up a brake caliper, rotor and mounting
hardware are all different types of metal. Rotor - ferrous steel, very prone
to surface rust but usually cleans off after a braking sessions.

Basically, any ferrous metal that is not galvanized or otherwise coated
against corrosion will develop surface rust when exposed for a time to
moisture. Does not have to be rain, can happen in really humid areas as
well. Surface rust does not indicate complete rust through.

> The piston, besides the different meatllurgy, is protected by
> the rubber seal.

what about the mounting knuckle?  last time i checked, the whole
caliper is orange (covered with rust).  the 2 bolts holding the caliper
to the mounting knuckle was free of rust; but will that stay rust-free,
or will the rust keeps moving onto other metal parts?