Are These Sport Calipers Usable
 

So i just purchased a set of 4 sport calipers and needless to say they are a bit worse off than what the seller described.

I have spent a few hours sanding and polishing the calipers to get them looking better but i need to know a few things before i go any farther.

the front pistons were very rusted in the center and top edge. i don't know about the outer walls since the piston is retracted. I purchased a rust removal gel compound and was able to get the flaky rust and most of the surface rust removed. i have used my dremel to grind/sand out the interior of the piston to clean it up, however it is not a flush/flat/completely smooth surface.
there is minor pitting and i am concerned about this.

the rear calipers don't look so bad but one of the pistons will not retract.

should i get a rebuild kit for the fronts? can i buy new pistons to replace the old ones?

I didn't pay much for the set, but again, i wasn't expecting them to be as rusted as they are.

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The outer part of the piston is important. Shoot a little compressed air into the fitting to release the piston. If there is any scarring, then you need new pistons. If the surfaces are clean and smooth all you need are new seals and dust boots and they should be usable.

i did some more polishing today. Hopefully i can get a good view of the pistons in the next few days.
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A rebuild is not hard or expensive. The fronts are easiest, the dust seal install has some tricks to it. The rears are strange inside if you'll be DIYing. You can check function pretty easily. I wouldn't be overly concerned about exterior rust.

Wirelessly posted

I had problems with severe pad taper on those calipers so good luck if you track it. On the street they're fine though.

Th beet method I've used for rust removal is sitting them to soak in white vinegar.

my goal is to clean them up enough so that i can paint them with black ceramic paint. I don't know if i need to get all of the brake dust off to the point where the bare metal is showing (kind of like i did with the fronts above) but i want the paint to stick properly.

i would love to find a better way to clean these up than using my dremel for hours on end.

Just wire brushing has worked well for me in the past. There are various paint products available that are quite sticky. Black is very forgiving and easily retouched too, I think your calipers will come out great with very little more work. Just watch out for brake fluid laying on the new paint when you bleed. Make sure you wipe it up quickly and the paint won't care.

Yes. I've blasted calipers and sprayed them with Duplicolor 1500* ceramic paint and never hat to retouch. Do black of course or I'll be forced to berate you.