Rear wheel alignment is easily divided between setting the camber (top and bottom of wheel tilted in or out) and toe-in/thrust-angle.
Camber first:
You need a (carpenter's) level. Oil up the adjustment cam on the inboard end of the original style strut rods, or clean and oil the threads on the (replacement) twist type aftermarket strut rods. Cut/buy 4 pieces of sheetmetal, smooth floor tiles, or heavy plastic about 1 foot square (larger doesn't matter, neither does shape, even round will do), and stack them in pairs with a film of grease between them, like grease sandwiches. Position the car on a spot that is fairly level across the car (left to right). It can run up or downhill a little (front to back).
Jack up the car at the frame in front of each rear wheel and insert the greased squares under the rear wheels, then lower the car. Push down on the bumpers a couple of times to reset the rear suspension. Put the carpenter's level vertically across the wheel or the tire (depending on the size of the level. Mine is 18 inches long. I put it on the tire. The rear wheels should be vertical. The car will squat with a load (wheels splayed out at the bottom). Since a passenger often rides with me on long trips, I throw 75 pounds of cat litter bags in the driver's seat to give a percentage more weight to the left side, and I like to align the car with a full tank of gas - which loads the suspension half way between an empty tank and 2 suitcases in the back with a full tank.
If the wheel is not vertical, Use the strut rod adjustment to make it so. Rest the car on the plates on the ground and push on the bumpers again, before checking the new alignment settings. Repeat as necessary.
Toe-in/thrust-angle:
With the camber set, measure the track width of the rear tires, about half way from the floor to the top of the tires, at the front of the tires and at the rear of the tires. For the factory spec 1/8 inch toe-in, the dimension across the rear of the tires should be 1/4 inch wider than at the front of the tires. If the toe is off by more than 1/16 (difference off by more than 1/8) the rear wheels need to be reset by moving shims at the front of the trailing arms (where they pivot at the cross bolt in the frame, in front of the rear wheels).
To determine which wheel has to be changed to point the wheels evenly toward the center of the front of the car, you need to draw a map of the wheels on the floor, I did it by making a tool to set in the wheel rim and scratch a mark on the floor in front of the wheels. In the attached picture, you can see the tool in the lower right corner, a piece of wood that fits in the wheel rim as shown, with a piece of angle iron screwed onto it to scratch the floor in front of the wheel. By scratching another mark behind the wheel and drawing a line between the two marks, I determined that my tool stuck out 1.5 inches outboard from the tire tread edge.
When I drew a line from a point 1.5 inches from the tire edge through the mark that the tool scratched in the floor, it points the direction that the rear wheel wants to roll. Since the front tread width is a little wider than the rear tread width (.375inch or .188 inch per wheel), I moved shims at the front of the trailing arms until each rear wheel pointed .45inch ( 7.2 times 1/16 inch) inward as measured at the front wheel tread center line. See the diagram on the attached picture. The reason for the 7.2 multiplier is to project the .0625 toe dimension of each rear wheel to the other end of the 97.75inch wheelbase. To determine the thickness of shims to move, divide the projected movement at the front by 5.5 (determined by dividing the 97.75 wheelbase by the 17.375 dimension to the trailing arm pivot). The two multipliers a(7.2 and 5.5) are necessary because the alignment spec is noted at the front of the rear wheels, while the shims are farther forward at the front of the trailing arms.
It sounds complicated, but once you map the car to the ground, it's not bad. I find this produces repeatable results. I am able to get the alignment right this way the first time. If I let laser alignment shops do it, every shop says the last shop got it wrong, and they can't align my front end unless THEY fix it.
I assume you know if the frame of your car is square (undamaged). If you are not sure, it can be checked at a shop, or you can check it at home by mapping the lower front ball joints and the lower rear trailing arm mounting bolt nuts to the ground to describe a frame rectangle. The diagonals (between LF to RR and RF to LR) of the frame rectangle you mapped to the floor should have equal lengths.
Here's a diagram and a picture to help visualize the instructions:
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