Vehicle: 2007 Cadillac Srx build date approximately April 2007 problem: Wheel lug nuts not staying tight. History: All 24 lug nuts found loose or finger tight (able to be removed by hand with socket but without using wrench) at 3,500 miles. Tightened by owner using owner's calibrated/certified torque wrench and returned vehicle to dealer for inspection. Dealer found all lug nuts tight. Dealer returned car to owner. Nuts re-checked and found loose on 3 wheels. Returned to dealer to inspect and tighten. Dealer found all lug nuts tight but broke one (1) wheel stud off tightening loose stud before reaching specified torque. Dealer re-checked the previously verified nuts and found 3 nuts on one wheel at less than the proper torque. No sign of wheel damage found. All nuts and studs threaded smoothly and did not appear damaged. No evidence paint acted as a shim thus preventing studs from achieving necessary clamping force. Conclusion: Determined problem is not that the wheel nuts were loose, but that they wouldn't stay tight. Possible cause(s): Defective studs with improper steel hardening or material. Hydrogen embrittlement of the hardened electroplated studs. Overtightened studs which stretched beyond elastic limit. Reason or time of possible over-tightening unknown; dealers records do not show wheels have been off the vehicle. Driving the vehicle with loose nuts from time of assembly (not likely in modern assembly line methods) or loosened nuts (cause unknown) which sequentially stretched each until fatigued. No evidence this could have occurred without deforming holes in wheel. Remedy: Dealer removed and inspected wheel and axle flange and replaced all wheel studs and nuts. Result: New studs are performing satisfactory and holding proper torque. Not known if old parts were kept.

- Dallas, TX, USA