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I have my pan all painted and put back together under a tarp. I noticed that my discs are getting surface rust on them and was wondering is there anything I can coat them with once I get the rust off? A light coat of primer/wd-40/phosphoric acid?? I know if left alone the rust will pit my discs. Any suggestions? Don't worry about it?

No on the primer. No on the phosphorus. WD40 or another light oil is ok, just remember to flush it off with something before you put pads near them. I'd recommend removing the pads until you are ready to use the brakes, I put small blocks of wood in the calipers of my Mustang so that if I accidentally hit the brake pedal, I don't shoot the piston out of it.

WD-40 is good for about 3 weeks. It is not a useful oil for protecting something that is not wrapped up and away from air and moisture. Short term it is good. The problem with putting phosphoric acid on the rotors is that it will convert the patches of rust to iron phosphate that will leave patches that will heat unevenly and wear unevenly during the first drive...and will never be really smooth again.
What you can do though is remove the bearings and seal, leave the races in.....take all the grease out with a paper towel and then wipe the recesses with solvent. Then dunk the whole rotor in 50/50 muriatic acid (swimming pool acid). It removes every trace of rust instantly and evenly. Rinse well...WD-40 quickly....blow it dry with air. Then paint the whole thing with automatic tranny fluid and slap it back on with greased bearings. I agree also on the remove the pads and use wood blocks. It can now sit for years with no rusting on teh rotors. Just be sure to solvent wash them when you get ready to run again. This takes about 30 minutes. Ray

Ray knows his stuff, go with what he says and you will be golden.

Thanks

Seems like a bit overboard to me. Not that I'm any kind of expert, but what worked for me;

I painted my rotors with a light coat of Zinc Chromate Primer before I put them on the car. Then 2 years later, on the first time I drove it I layed on the brakes hard the first time. The pads scraped the primer right off. After a couple stops they looked like I had just put them on.

But I did this as I installed them and had no rust on them to begin with.