Reply to "Leaking Caliper Piston"

Actually, those 'ATS' calipers are stock aluminum two-piston units for a 1970 911S. I adapted them to the rear uprights and balanced them against stock Girling front calipers first, then Wilwood Superlite 2s, both with a manual proportioning valve.

The Wilwoods went on after we lost the stock fronts on a 1000 mile Fun Rally round trip to 'Vegas & back. My wife drove the mountain route entirely on the rear brakes and said the brake pedal was 'a bit long in travel' but she had no trouble keeping up with the other dozen Panteras in the group. We trade off driving; I drove home the same way and also had no trouble.

I've since added Porterfield R-4S pads & Speed-bleeders on both ends, after the ATS sprung a leak. I used 312 stainless bar stock to make 4 pistons after I found both the Girlings and ATS calipers had plated pistons. I checked an aluminum Girling Mangusta caliper last year (same as big-block Cobras) and its pistons were also magnetic.... Change brake fluid EVERY year!