Are there two versions of the S caliper?
 

Here are four pics of S calipers. One is my car, one is from Bill Verburg's page, and the others are from the web. As you can see, the top two are clearly a different design than the bottom two. Does anyone have any information about the two designs? Are they functionally identical (same piston, same pad)? Did one supercede the other at some point?

http://www.rallystuff.com/images/scal1.jpg

http://www.rallystuff.com/images/scal2.jpg

http://www.rallystuff.com/images/scal3.jpg

http://www.rallystuff.com/images/scal4.jpg

Jon,

The two lower pics are not 'production' S calipers ... they are the Ate racing calipers used on various versions of the 906, 910, 909, 907, and 908 race cars from 1967. The famous 'gruyere' cross-drilled rotors were developed first using those calipers on a 908 around 1970 ... for use on the Mulsanne straight, specifically!

After browsing around the web I've seen them (the lower two pics) referred to as 908 calipers and 914-6 GT calipers as well as just plain 911 "S" calipers. In fact unclezak is Ebaying a set right now as "911 Carrera S alloy brake calipers":

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2402874082

So you're saying these calipers never came from the factory on a 911?

I have seen the 2 versions on street 911s, but only the top ones on RSs. I have pairs of both types, and they seem pretty much the same, except for the obvious contour difference to the outside; the pistons are the same diameter.
One difference from the pics is that all have 2 pins for the pads, not the one "double pin", which I'l be duplicating.
GeorgeK

I figured it out from the part numbers.

The top "S" caliper is the later version introduced in 1972. Part number 911-351-935/6-00.

The bottom version is part number 911-351-975/6-10 and is listed through 1971.