The Very First S-Caliper?, an interesting look at one of DaveP's calipers Options

[Eric_Shea]

Dave Pateman sent some S-Calipers down for a dichromate re-do (not these in the thread, a later pair off a 73+ car) and he graciously sent an odd-ball caliper he had laying around for me to have a look at.

It sure proved interesting and, I have my "theory(s)" as to what it is and how it, and the following S-Caliper lineage came to be. The theory goes like this:

Porsche has been well documented in proving a concept at the track and then positioning that concept on their production line vehicles. I believe that ATE was commissioned to make a lighter caliper for their racing vehicles. I believe what we're about to see is one of the first basic S-Calipers to exist.

On with a tale of two S-Calipers:



Mine's on the left. It's a reconditioned, very early (69-70) S-Caliper that I will be using on my GT car. Dave's one-off is on the right. The first glaringly obvious difference is the endurance pad pin assembly. Any car that is going to go through S-Caliper pads in a single race is probably going at it for 24 hours.



Upon further inspection, this caliper was finish machined slightly different as well. The tops were flattened but only by a small amount. Various logos and markings are not in the usual production locations and there's a few "niceties" that would be missing. I'll try to cover it all herein.

First let's look at the bottom side logos. Both are "basically" in the same place but, the casting lines from the production caliper (red arrow) is missing and the logo is centered (refinishers buffed the other logo a tad much):




The flute around the pad cavity is slightly different. These calipers are nearly identical with the exception of some of these things which lead me to believe a later production model was molded off the same casting. The later flute is slightly deeper:




Again, markings and castings are slightly different. I do not believe the 68 represents a year. Mine have similar markings elsewhere on the caliper and they're something like 33. I would guess a finisher stamp??




Here's one of the convenience things or "niceties" I found. It's a pain in the @$$ to get S-Caliper lines and bleeders off. These must have been a bear. Note how the later production model caliper differs:




This stamping on the machined top tells me this was no afterthought to make it fit a certain wheel. The race dept. probably worked closely with ATE for these specs.:



Here's the two side by side. Again, proportionately these calipers are identical. You can see how they finished the top on this caliper:



On the side of the nose of the caliper there's an odd bump, possibly denoting the back of the piston chamber. The production model bump is more pronounced:




Here's a little more detail on the quick-change endurance pad pin. While this was a rather crude adaptation to the original caliper, I do believe it falls right in line with a factory race look and feel. I'm fairly certain this was an original mod.:






Pistons are different. The one-off has a very deep piston top. The standard S-Caliper piston is pictured in-hand:




The pin assembly itself is rather crude and not even but again I think this is a factory manifestation. I've seen these pins on one other set of calipers but without the latch mechanism. All in all, it was an interesting afternoon (for me anyway). Here's a full-on shot of both calipers (pay no attention to the two pair of original GT calipers in the background!):




What are your thoughts?

[davep]

here is an interesting thread I came across in my research:
http://forums.pelicanparts.com/showthread.php?t=169568
I have a few emails out to the fellows involved trying to learn more.

It would appear that the caliper evolved from the 910 style with the round back cover to the more familiar S caliper.
Varieties of the caliper were made to suit particular applications.
The most familiar 908 variety with the bottom pins and plate was an endurance caliper with thicker pads. However the single pin for pad release seems to stick out quite a bit, and may not be suitable for rims less than 15" diameter. My caliper is shaved down and would fit smaller rims better. Therefore I think we need to look at cars that used the smaller rims.

[Jeff Hail]

here is an interesting thread I came across in my research:
http://forums.pelicanparts.com/showthread.php?t=169568
I have a few emails out to the fellows involved trying to learn more.

It would appear that the caliper evolved from the 910 style with the round back cover to the more familiar S caliper.
Varieties of the caliper were made to suit particular applications.
The most familiar 908 variety with the bottom pins and plate was an endurance caliper with thicker pads. However the single pin for pad release seems to stick out quite a bit, and may not be suitable for rims less than 15" diameter. My caliper is shaved down and would fit smaller rims better. Therefore I think we need to look at cars that used the smaller rims.

Going back to my original post.........Hans Metzger of Porsche typed model 906/2000 which was known as the Ollon-Spyder. This model first appeared at the Swiss Ollon-Villars hillclimb event. Metzger took inspiration from the Elva-Porsche. This model used exclusivly 13 inch front wheels. Porsche at the time did not make 13 inch wheels and had them produced from an outside source along with revamped uprights. The original wheels were steel would have had a barrel thickness of approx 1/4 an inch. This would have meant shaving any parts including calipers to clear the new wheels. The steel wheels used a reinforced center section extending into the barrel shell requiring even more clearance. The calipers at the time would have to have been experimental or cast and machined for the smaller wheels. As well as the prototypes class (called group 6) aimed at the big manufacturers they also defined a class for competition sports cars (class 4) where a minimum production number of 50 cars was permitted. Piech saw an opportunity in the new ruling, but was convinced that Porsche would need a completely new chassis and car. He decided to use the Ollons-Villar spaceframe chassis (not the 904) as a starting point.

The 906 (or Carrera 6) used both steel wheels and magnesium. Applications included 13 inch wheels for up to 2.0 liter versions. The Daytona running 910 also used 13 inch wheels and would have had to use the early shaved calipers. The long tails had brake cooling issues and were than updated with 4 piston calipers and ducts to alleviate cooling problems at the high speed course's. In late 1968 some calipers were updated again to magnesium bodies from the previous aluminum versions for weight savings. Porsche returned to aluminum calipers as the magnesium versions had problems associated with high heat. Even later updates on the 908 and then 907's all wheels were updated to 15 inch. This allowed the use of larger calipers and ventilated brakes to be utilized. The 908 with updated wheels and calipers stopped better than any other previous racing Porsche.

Based on the factory documentation and Erics' information the timeline is narrowed even more on Dave's caliper. Based on the inspection marks I honestly believe he has a real Mccoy 908 racing caliper and not one that appeared on a 914 GT as off the shelf racing parts. Adding Porsche has always used the 20% safety margin (or over-build) on it's racing parts unless unavoidable. I cannot see a logical reason for the factory to shave calipers unless it was for smaller diameter wheels. The factory never skimped on brakes. The 907 units used entirely different calipers and then that eventually evolved into the 917 model.