I recently had to change brakes for the first time on my Aerostar.
When I got the wheel off, I was surprised to find no bolts!  Looking
for help on USENET, the only thread I could find that addressed how to
do this was this one
http://groups.google.com/group/alt.autos.ford/browse_thread/thread/5c4f3e91c9d9c
415/16812aa6335f259c?lnk=st&q=replace+brakes+aerostar&rnum=1&hl=en#16812aa6335f2
59c
but the poster never did say how to do it, and while I did figure out
how to remove the calipers, the thread is too old for me to reply to,
so I am starting a new one.  Disregard if this is common knowledge;
this is for poor, ignorant folks like me.

Ford Aerostar brake calipers, at least on the model years 1992 (mine)
and 1993 (the original poster's), use spring-like spacers to wedge the
calipers into place, rather than bolts.  Once you see them, they jump
right out at you.   On either side of the caliper itself, you will see
small steel plates with some type of elastic between them.  Two of the
plates are on either end of the caliper itself.  You simply punch them
out with a hammer and a regular screwdriver, and let them fall out
behind the caliper.   Pull out the caliper from the larger frame
holding it, pull the old pads out, spread the caliper open with a
C-clamp, slide the new inside pad into position behind the rotor, snap
the new outside pad into the caliper, and slide the caliper back into
its orignal position.  Hammer the bottom spacer back into its original
position, then hammer the top spacer back into its slot.   Put the
wheel back on and you're good to go.