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Question about upgrading from lip seal to o-ring pistons: I always see people saying to get the old calipers sleeved. Is this absolutely required for some reason, or for more of a cautionary measure to hedge against old, possibly pitted bore walls?
I noticed when I took apart one of my ‘82’s front calipers, the bores on one caliper half were much brighter and smoother in appearance (bottom in pic) than the duller ones on the other half (top in pic). It also appears to me that the shinier bores have a slightly wider “lip” than the dull ones, but maybe that’s a trick of the light. All four bores in the other front caliper were dull in appearance.
In contrast, I just picked up a caliper from a ‘78 from a salvage yard, and all four bores on that one are shiny in appearance! Is it possible that only one half of my caliper was sleeved, or is it maybe none of them were and this is just a difference arising out of the manufacturing process? I don’t know what a sleeved bore looks like compared to one that isn’t.
Ok so I guess it was more than one question. Any help is appreciated.
If I recall back a long time ago when I had my C2 and stainless sleeves were first introduced, the idea was that there was an issue with the aluminum pistons and the cast iron caliper. Add a little moisture and the pistons corroded, right between the seals and the pistons. The stainless sleeve prevents that corrosion between the 2 metals.
The sleeving practice began because the original cast iron bores rusted, followed by pitting, when brake fluid absorbed moisture (which it does as a normal downside of DOT 3 and 4). Pitted bores leaked and allowed even more moisture into the system. Sleeving was a good solution to stop moisture from degrading the bore surface and keep the caliper functional.
Both of your caliper halves shown have stainless sleeves. You can see the small seam where the sleeve is resting on a lip in the original bore. I'm guessing the differences you see in the bore chamfer is due to either different machining shops or just different time periods when the machining was done and what sleeves were available. Corvette calipers have been sleeved and rebuilt for over 40 years, so it's very likely that your pair of halves were mated to other halves sometime in the past.
SS sleeves can and do stain a bit but absolutely shouldn't rust and pit. You can polish your existing bores (brand new ones are almost a mirror finish, a bit shinier than the foreground sleeves). If any portion of a bore is scratched such that it catches a fingernail or dental pic I'd recommend changing the caliper out.
Depending on how much polishing is needed, I'd start with wet/dry 800 or 1200 or 1500 grit paper lubed with WD-40 and work my way up to 3000 grit. At this point the bore should have super-fine scratches but nothing that can be felt. I didn't use metal polish beyond this point as the bores looked much better than when I started and they've sealed well for several years now.
Generally, we hone them with a small 2 stone brake hone. Leaving a fine cross-hatch. We do not polish them.
A fine cross-hatch will seal well against the seal.
I was thinking when reading this post, at first glance, that there is no way an 82 C3 corvette has OEM GM factory cast iron bore calipers with no rust after 40+ years sitting in Hydroscopic brake fluid............
I was thinking when reading this post, at first glance, that there is no way an 82 C3 corvette has OEM GM factory cast iron bore calipers with no rust after 40+ years sitting in Hydroscopic brake fluid............
I totally agree, which is why I felt weird even asking the question, but the number of shops that I physically took the calipers to who insisted that only some of them are sleeved is disconcerting.
You definately have the SS inserts in both of yours.
I can see both the thin SS lip edge, on the outside, as well as the lip at the bottom of the bore.
Brake Upgrade Question
