Leaking calipers
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,135
Likes: 4,245
From: US-PNW
As for the OP's issue, it seems that once significant corrosion gets into the o-ring pocket between the halves, that caliper is done. Perhaps it could be machined, and a larger O-ring used? You can see the pitting starting in @Rescue Rogers' images above. Fortunately, the O-ring is still working.
Of the calipers I've rebuilt, the pocket appears just roughly countersunk and not a finely done sealing surface. As I understand it, they rely on significant squish of the o-ring to seal. The large mating surfaces have always appeared to be as-cast or minimal file clean-up but certainly not precision flattened. If one flattens the large mating surfaces on a plate or some such, the depth of the o-ring countersink will be diminished and therefore have a better seal.
Le Mans Master
Joined: May 2007
Posts: 5,025
Likes: 1,120
From: North tonawanda NY
So to be clear, these are all sleeved calipers with the O-rings. The leaks are all coming from the seal between the caliper halves. When I disassembled the first ones I found crud and corrosion on the mating surfaces which I cleaned up with a wire brush and scotch Brites. The recess for the small o-ring looked shallow but decent enough to make the seal so I torqued them together and assumed it would work. The one that was leaking is now fine but the other one that wasn't leaking is now leaking. I don't want to go through this again so I'd like to find a source for reliable, well built calipers. I'm guessing Lonestar will be my best bet..
