Give me the best way to measure front end, rear end, crossover whatever to get the best idea if I have the car square. I just reworked the rear axle with radius rods and coil over shocks. Now I want to make sure the rear end is straight with the front end etc. Of course I bought this car and don't even know if the frame is square itself but I want to be able to get it as close as possible. Oh, also pinion angle.
string and tape measure. Run a bunch of string diagonally from the rear end to points on the chassis. Do this symmetrically from the left and right side( body mount locations work well). Do the same to the front. Measure the distances to triangulate center. Now snap a centerline. Just move stuff around until they all jive. I usually set the pinion on a parallel line(not necessarily the same line) with the engine/trans. Then depending on the spring type, nose it down. Leaf springs 8-10 degrees. Coil spring 2&4 link 5 degrees. I am sure there are other ways to do this.
Takes some time. Set front toe to zero and perfect straight ahead, easier said than done. Run strings the length of the car PERFECTLY parallel to the front tires. The measurement at the front edge and back edge of the front tire have to be exactly the same on both sides. If the rear is square the measurements at the front and back of the rear tires will be the same as well. Using any point on the chassis is only as square as the chassis. Bent racing wheels don't work well for this either.
Plumb bob from fixed points on the chassis, the more the better as long as they are the same point on each side then take a chalk line and make X marks on the floor, snap a line down the center, if the line goes through the center of all the Xs your chassis is straight, thats how I did frame repair for years.
I set the air pressure in the tires and level the chassis on stands to take the springs out of the equation, then I use a plumb bob to drop lines all over the chassis, marking the floor at every point. Be sure to mirror both sides. Use the front or rear of bolts or rivets, not the center. It's easy to be off a little when you eye-ball stuff. I use a lot of sharpie markers and make notes on the floor to help me remember anything I noticed at that point. then you can pull a bunch of diagonals with a tape measure to check for square. remember to find and drop the centerline at each cross-member and drop any points down each side that would be parallel to the centerline. Pull a string on these to make sure they are straight. It isn't uncommon fro a car to be bent in the middle and have one end left or right of center. Probably 1/3 of the chassis I have worked on had that problem. When you have all the chassis points mapped out, the go on to set the alignment. Use a large framing square to check the wheel track to axle for square, set toe-in and find fixed points on the body in the middle of a curve.
I usually set the pinion on a parallel line(not necessarily the same line) with the engine/trans. Then depending on the spring type, nose it down. Leaf springs 8-10 degrees. huh? you must be the guy who hung the rear in my old chevy. trans at 3 degrees down, and pinion 4 degrees down. if the trans is 3 degrees down you want the pinion 3 degrees up.
While the various methods suggested all have merit.......and it IS desirable to have a frame that is "square"....to get the rear end aligned, first make sure it is centered from side to side, then determine a center point near the front of the frame and measure from the same point on either side of the rear axle housing/hub to that center point.......with the axle centered side to side and the diagonal measurements described above, the rear end is both cenetered and 'square' with the frame. Do the same for the front end using either a straight axle or independent A arm type. I like to use the Lower ball joint center for A arms (or the equivalent point for pin style joints)........best wishes
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