Bicycle Mechanics - what kind of caliper brakes do i need?

i need new brakes for an old bike, and don't know which ones to use.
i got an old cannondale touring frame from a friend of mine. he's gone now (touring in another state) so I can't ask him.
I don't know the model, and can't find any serial numbers.
the bike is

a cannondale
aluminium,
with 27 inch wheels,
five speeds in the back,
and a steel fork.
it had diacompe caliper brakes which sort of... fell apart one day.

my first question is: does anyone know what model bike this is?
my second question is: what brakes do I need for this bike? my friend said something about shimano 105s not working unless i drilled out maybe 2 mm of the frame, but that they would line up properly.

You can get Shimano dual pivot caliper brakes in std reach and long reach. Measure the drop (C-C) from the brake bolt to the brake-block bolt.
For more info see here (http://www.rivendellbicycles.com/html/101_sidepull.html)

You probably have an old Cannondale touring bike like mine... Although mine is 18 speed (6 in rear) so yours may be a year or two older. Mine is a 1989.

The brakes on older bikes used a non-recessed nut, and the posts that hold them all together were longer.

In general the easiest thing to do is to find an old pair of quality brakes similar to what you have. People in the Classics and Vintage subforum may have some sources to share, or check out thrift store bikes for a nice parts bike...

If you want new brakes, check out Sheldon Brown's site for information on what to do... In brief you will want two front brakes... One will go on the back with a standard nut and one will go on the front after drilling out the back of the fork to the appropriate size for the recessed nut. I believe that some brakes may be sold with the older style (non-recessed) set-up, but they may be hard to find.

Good luck!

You likely need what are now called "long reach" brakes (usually 47 to 57 mm range). Shimano and Tektro both offer these currently.

If you need to use recessed nut mountings, drill the back (ONLY the back) of the fork crown brake mounting hole out to 8 mm or 5/16" and the front (ONLY the front) of the rear brake bridge the same.

found some on craigslist. they work fine from what i can tell. thanks for the help.