Remember this is your steering. If you're not familiar with any of the terms or procedure it may be best to leave it as is.
From 87 rear drive manual:
"Sector Shaft Adjustment
(1) Disconnect center link from steering gear arm.
(2) Start engine and run at idle speed.
(3) Turn steering wheel gently from one stop to the other, counting the number of turns. Then turn the wheel back exactly half way, to the center position.
(4) Loosen sector shaft adjusting screw until backlash is evident in the steering gear arm. Feel the backlash by holding end of steering arm between thumb and forefinger with a light grip. Tighten adjusting screw until backlash just disappears.
Continue to tighten to 3/8 to 1/2 turn from this position and tighten locknut to 28ft.lbs. (38N.m) to maintain this setting."
It doesn't say, but I shut the motor off for step 4.
With all of that done you should not be able to feel the box come over center. If this is not the original box, you might do well to make sure the steering arm is on the box in the right position. It can go 4 ways and I've seen them on wrong. If you do this adjustment without the box centered it could jam as you try and turn the wheel. Not a good idea on the road, thus my warning, procede with caution.
BTW, I've done this adjustment on 2 cars and on C class motorhome. Worth the effort.
Have someone gently rock the steering wheel back and forth while you watch everything from the the steering column shaft to where it enters the box
to where it exits the box
the pitman arm to center link joint
the center link to idler arm
the idler arm to frame
all 4 inner and outer tie rod ends
upper and lower ball joints
upper and lower control arm joints and suspension/support bushings
Make sure that nothing moves more than the part that it connects to. If you see this excessive movement, that is your worn component.
Usually but not always, if a box is worn enough to require a sector shaft adjustment then the worm shaft is worn as well. Worm wear is seen as a slight in/out movement at the point where the steering post enters the box. That adjustment requires removal from the car and special tools. By that time it is probably worth getting a reman box.
Always follow the troubleshooting and service procedures stated in the factory service manual. Use safe jacking practices and always use jack stands while under the car.