definitive word when to toss caliper due to corrosion?

[911SCfanatic]

Did lots of searches on rebuilding calipers that discuss corrosion or pitting. General consenus seems to be that some corrosion/pitting on both the piston and bore is o.k. If you agree, how much?

Piston: I have some pitting on outermost 1 or 2 mm of the piston. Is this o.k.? Seems that this portion of the piston would never reach the seal to cause a leak.

Bore: My bores are corroded from the seals outward. I would think that as long as this doesn't cause the piston to hang-up it shouldn't matter. Also, how would I hone the bores (in particular the area outside the seal) without splitting the caliper?

Thanks.

[dweymer]

As I am rebuilding mine I was wondering the same thing...I lightly rubed my pistons with 2000 grit wet sandpaper, around the pistons. It did not take much to remove the gunk. I would think anything there(that far out on the piston) would just create more friction to overcome when the pedal is released, not cause a leak though. Same with the bores, I just cleaned them up so the pistons will retract smoother. They are in the paint booth right now(guest bathroom) or I would post pics.

[911SCfanatic]

Let's get some more thoughts on this one.

[David]

Some pics would help.

On my kart brakes I'll bore them out a couple thousandths and put in new seals. With more that a couple thousandths, I'll make new pistons to close up the clearance.

To hone or bore the piston bores you'll need to separate the caliper halves.

[randywebb]

If you clean them up some with a hone, etc. -- can you still feel pits when you rub your fingertips on them?

Pretend you're a machinist and feel them - you can feel the thickness of a sheet of paper....

Then you want to think about the cost issues re replacement vs. working on them, and are they rare calipers - are they "S" calipers?