Originally posted by SteveBuchanan:
'It looks like the extended upper rear a-arm can help to solve the problem with too much negative rear camber when the car is lowered. Thus our goal is to have zero or slightly positive rear camber when the car weighted. This is to avoid excessive inner tire wear. Am I correct?'
Steve, your goal above is correct. But the problem, typical of a powerful 45-year-old spot-welded sports car, is that various parts of the rear monococque are gradually collapsing; spot welds are breaking or distorting and that badly affects the rear wheel alignment, whether or not the car is lowered. So adding extended upper rear a-arms does not correct the problem but simply corrects existing wheel misalignent, which will continue to change. There are two MORE possibilities for addressing the problem.
1)- by adding an adjustable bay-brace-bar with an extended nose section- such as Hall's straight steel bar to replace the dog-led stock bar with NO adjustment, camber alignment correction can be gradually added in while better supporting the whole rear suspension. Basically, you jack up both rear wheels and crank in 'some-but-not-all' needed pre-load with the bar's center adjuster, lower the car, check camber and drive it that way for a few days, then repeat until your rear camber is tolerable- typically less than -1 degree.
WARNING: trying to add in ALL the needed correction at once may buckle the rear fenders or quarter panels. Be patient and let the sheet metal/chassis relax in between adding correction stresses.
2)- The real fix is to first do the above, then seam-weld the entire rear of the car to supplement the original spot-welds. This better supports the camber correction from the bay-brace preload and markedly improves the Pantera's handling, according to those who have done the full correction. But for many Panteras, doing only Part 1 seems to satisfy them. A third possibility is to have a professional shop correct your sagging subframe. Wilkinson has a frame jig and the spec's, and has done this for some Panteras.
Note that Dallara cautioned DeTomaso on this very thing in 1970 before the car was released to the public, but DeTomaso poo-pooed his fears, famously replying, "Don't worry- streets in the U.S. are as smooth as a baby's bottom!" Don't know what part of the U.S. road & highway system A. DeTomaso was referring to....