911 Changing Front Calipers
 

Hi. I'm gonna swap out the M calipers for A calipers on my 1973 911. Does the footprint / padprint change as far as how the pad meets the disk? Or: my disk has some wear on it. Will the increased size of the A caliper pad fit outside of the wear area made by the M caliper pad?

Thanks, John.

You can not just swap A & M calipers.

The A and S calipers need struts which have 3.5" mounts

M calipers have struts that are 3"

The A pad is slightly larger than an M

On a '73 the rotors are the same.

So to use an A caliper on you car you first need 3.5" struts, then it all just bolts up

Right: I have the proper struts. The question remains: do I need to also change roters because of the current wear patterns. I know that the pads are larger, the question is: will the new pads overlap the current wear pattern on the rotors.

John.

When you bed in the new pads they will mate to the rotor surface.

I understand that they will bed... eventually, but what happens when I put them on: is there a misfit, how large is it, and is it dangerous, which gets back to the question: do I need to install new roters?

John.

Ok, now I see what you are asking.

the M pad is ~14mm shorter than the A, so no, the footprint won't match.

New rotors are cheap for that app.

Thanks, Bill. I was thinking that way, but if the shape had been different, it might have worked. Yes, they are cheap. Now I have to decide: drilled, slotted, or plain. It's always something :-)

John.

plain old factory is what you want