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Although the front disk brakes of the early 240Zs was considered quite a sporty feature compared to the front drums more common at the time, replacement with more modern calipers and rotors can significantly improve braking in your 240Z.
I've had a variety of brake problems with my 32 year old 240Z, such as a broken parking
brake cable (that can prevent self-adjustment of the
rear drum brakes), bleeding problems, and corroded caliper pistons. Over the years,
I replaced the cable, put in speed bleeders, rebuilt the calipers, and switched to
semi-metallic pads. Still, the first couple of stops in the morning just kind of
glided. Worse yet, sometimes in freeway panic stops I pushed harder without feeling
the expected additional stopping power. Part of the problem was my glazed solid
rotors and the stock 240Z 2-piston calipers.
The stock 240Z calipers use two
hydraulic pistons to squeeze the rotor between a pair of essentially square friction
pads. The stock rotor is a solid unslotted disk. This design can be improved
with additional hydraulic pistons pushing bigger pads onto a slotted rotor.
The 4-piston calipers from a 1979-1984Toyota
4x4 happen to have mounting bolt holes arranged to fit perfectly on the 240Z brake caliper
mounting brackets. The Toyota friction pads are curved rectangles that extend across
the two pistons on each side of the caliper to contact a much larger rotor surface.
The four hydraulic pistons provide a larger cross section for a greater multiplication of
brake pedal force. I purchased drilled and slotted rotors from Motorsport Auto
(1-800-633-6331) to further improve the system (although the Toyota calipers will also fit
the stock Datsun rotors). The rotor drilling and slots are said to enhance cooling
of the rotor and increase friction by allowing gasses to escape the frictional contact
surface between the rotor and pads.
Removal of the stock calipers and
rotor: 1) jack up and redundantly support the Z; 2) remove the front wheel; 3) disconnect
the flexible brake line at the wheel well mount and plug the line to prevent spillage of
brake fluid; 4) remove the caliper mounting bolts and lift off the caliper; 5) pull off
the bearing hub dust cap, remove the castle nut cotter pin and the castle nut; 6) 
pull the hub assembly off the spindle; 7) turn out the 4
bolts that fix the hub to the rotor (brace the hub with a large screw driver positioned
between the wheel studs); and, 8) separate the old rotor from the hub (I used a blunt cold
chisel with light taps at different positions between the hub and rotor until they parted;
it seems I could have alternatively placed the rotor across a couple of wood blocks and
knocked the hub out with a mallet).
The only modification required to
install the Toyota calipers is to trim away small sections of the baffle plate to allow
clearance for the longer calipers. I used a hand held angle grinder to remove about
1/2 inch of the baffle (you could probably use a hack saw). As I ground, I kept
checking the caliper fit and removed the points of contact until the caliper could be
installed without interference. A lot of metal filings were produced - keep your
bearings out of the area and clean the spindle well before starting reassembly.
Assembly, with the new caliper and
rotor is the opposite of removal steps. Before reassembly, check the inner and outer
bearings and races for scoring; check the rear bearing seal for damage.
Replace any damaged bearing parts. Pack the bearings and hub with grease.
Assembly: 1) pull the rotor evenly on to the hub (left rotor on left hub, right rotor on
right hub) by progressively and alternately tightening the 4 bolts that fix the hub to the
rotor until the rotor is seated; 2) torque each of 
the
bolts to 20 foot-pounds, then each to 35 foot pounds, while bracing the assembly with a
large screw driver (as shown in the photo above); 3) remount the assembly on the spindle;
4) with the rear bearing well seated, and the front bearing and bearing washer in
place, turn the castle nut in until hand tight; 5) spin the hub while you tighten the
castle nut to 24 foot-pounds, then turn the castle nut back to the first available
position that allows the cotter pin to be reinserted; 6) replace the bearing hub dust cap;
7) install the new caliper over the rotor (friction pads can be in place at the time, or
not; there are right and left calipers, so be sure the larger piston and the bleeder valve
are up) and turn the caliper mounting bolts into their threads - torque to 75
foot-pounds; 8) connect the Toyota flexible brake line at the wheel well brake line mount
(be sure the flexible brake line will not touch the wheel during turns); 9) bleed the
brakes; 10) remount the wheel; and, 11) carefully test drive.
With the upgrade, pedal pressure to stop was less. With hard stops, a little more pressure always gives me more stopping power.
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