S vs A calipers?
 

I am looking to buy a "911 Backing Plate, Black Anodized (Left), 911 (1969-89, with 3.5" bolt spacing, S or A calipers)" from our host. I have stock Carrera 3.2 brakes.

I just wanted to verify the nomenclature for the brakes... the S vs A calipers. What is the difference? Are we talking SC vs 3.2 brakes?

Search does not like S or A, but I am happy to searh more if someone can give me the "buzz words." Either way, I expect this is a quick answer.

Thanks for any help

Edit: not sure how i got this in the engine forum... Oops.

Answer: Wide a calipers on a carrera.

PMB - Mid 911 Brakes

S calipers are the aluminum calipers first used in the 1969 911S on through to the first turbos; and versions for the 908. The A caliper used the same size, but thinner pad, and is a cast iron caliper in a couple of widths.

The A was used from '76-83 on Carrera and SC cars. It uses the same 20x282.5mm rotor and 3.5" strut mount as previous years S calipers used on S, Carrera and 930(til MY'77) cars. A are iron bolt up designs S are aluminum 1 piece designs.

The wide A was used on 3.2 Carrera from '84 -89. It is the same caliper as previous A but has a thicker spacer piece in the middle. These use a 24x282.5mm rotor.

Either S, A, or wide will bolt to the same 3.5" strut, all use the same pistons. Either 20 or 24mm rotor will bolt to any 911 hub. The S and A must use the 20mm rotor( I have seen an A on 24mm but the much of the pads friction material had to be shaved to do it. Wide A must use 24mm rotor.

A small brake upgrade for SC or earlier Carrera is to use the wide A caliper and rotor w/ stock rear M caliper and rotor. This retains the excellent 9 bias seen in all 911s through '83.

Similarly '84 can leave their front alone and chnge the rear to the regular M rear using the regular M 20mm rear rotor instead of the wider 3.2 Carrera 24mm rear rotor and wide M. This gives the car excellent bias once the stock p/v is removed.