Before I take down the CTS suspension cradle I need to get a location on the spindle center line. I need a reference point so I am using the rear cradle mounting bolts. I used magnets to hold strings with weights to the center of the rear bolts right and left. Then I laid a spirit level over the top two lugs on the rotor and rotated it until it was level. In this position, the bottom lug is at the center of the spindle. Dead on 6 o'clock. Then I hung strings and weights on the lower lug to represent the spindle center line. I set up the laser to hit both strings on the cradle bolts, then used a measuring tape to measure from the cradle bolts forward to the spindle center line. 5 inches in this case.
Next, I need to set up a datum line. This will basically be an imaginary level deck below the frame in the area I'm working on. It only needs to be straight, level, and firmly attached. I am just using some scrap angle iron that I had around. You can use whatever gets the job done just be sure it's not bent. I tacked the vertical pieces to the frame and clamped the horizontals to them. I didn't weld them because I want to be able to adjust them.
This does not represent ride height! It is to locate dimensions from the CTS spec sheet and transfer them to the 49. The print out with the frame specs are used to set up and and measure on a frame machine. I will add to the datum line dimensions and get ride height later. For now, I am looking for a level surface to measure upward from.
Above is the spec sheet for the CTS. You can see by the two arrows and the red circle, where the lowest point of the frame is on the CTS. It's 4 1/2" off the datum line. I will also have a similar spot on the 49 where the frame starts to kick upward toward the front suspension. The frame is straight and is the lowest point on the bottom of the car. When I have measured and double checked everything, I will probably add 1" to each datum line dimension to set my ride height at about 5 1/2". This car will have air suspension so I can raise or lower the ride height at will but I want normal cruise height to be in the "sweet spot" of the suspension travel. Right around the middle of its travel range.
Both sides done. You can see some of the reference marks on the frame. From the front back are front cradle bolt, spindle center line, rear cradle bolt, and cut line.
