Originally Posted by dddd

Cabling needs to be almost entirely free-moving, with little to no detectable "losses" with respect to uptake and release of cable as the lever moves.

Calipers need to be free-moving on their own, again with return force completely smooth as when applying the brake. Lubricate and adjust pivot tension as needed, also lubricate both ends of the return springs where they meet the little stops on each arm.

***Cable housings need to be of sufficient length (relative to handlebar position) so as to allow each caliper to "float" on it's pivot instead of being pulled/biased toward one side.
Check this AFTER swiveling the bars back and forth to the limits.

The brake pads being thirty-something years old are not likely to give good braking even with the the cables in good shape, though sometimes an exception to this arises. Shimano pads usually don't age well at all as compared to DiaCompe or Suntour pads.

The Tempo was a very good (and good-looking) bike, excellent road frame geometry and with good modest componentry, as long as the bike's (French?) hubs weren't set up with over-tight adjustment as was so often the case with 1980's Schwinns. ***There must be some bit of free-play in the axle bearing's adjustment to account for the axles shortening in response to the quick-release levers applying tension over the length of the axles!
Your later-model (1988?) Tempo likely has the superior Shimano freehub system hubset.

The later Tempos with indexed shift levers will by now need to have each lever pivot lubricated with light oil dripped into the space under the mounting screw/washer, thus giving free movement and solid (loud) clicks at the right lever. Also be sure that the cable is lubricated at the bottom bracket guide.