Caliper types ?
 

I need to order some brake hardware for my '77 911S, what's the difference between S-calipers and M-calipers and how do I tell which I have ?

S calipers are aluminum, M's are steel. Look on the pmbperformance website for pictures of each.

A '77 S is unlikely to have the aluminum s calipers unless a P/O installed them.

The other 2 possibility's are iron A or iron M

If the front and rear calipers are the same size and use the same pads they are M, if the front uses a bigger pad and is iron it's an A.

In addition to the A calipers being steel, the spacing between the mounting bolts is 3.5" (for both A and Aluminum S Calipers). The bolt spacing for an M caliper is 3".

Also, the Carrera uses a Wide A Caliper. The space between the two caliper halves has a wide spacer (wider than the regular A). The Carrera Wide A requires a Carrera Rotor that is also wider that the SC Rotor.

PMB Performance has a good website with photos of all the different caliper types Brake Restoration Service

Gentlemen---- Excellent advice as always. I thank you, and my car thanks you !

Your '77 came with As front, and Ms rear. The S calipers last appeared on some of the '74 Ss, and again on the early Turbos.

The '74 and '75 non-S cars came with the 3" brake mounting spacing struts, and an M caliper. It was not the same as the M caliper which went on the rear, as it had larger pistons. But same pad size and mounting spacing.

By '77 Porsche had done away with the non-S model, so it was As front and M's rear. Those are the pads you want, and the rebuild kits as well.

However, if someone has switched struts, you could have Ms in front. Or, without switching anything, the S. Very easy to tell which is which. If Carrera As and rotors were added, that would be a bit trickier to tell.