I'm having a chronic problem with the front suspension U bolts loosening up on by 90 Blazer. I would tighten them to spec's and after a few month of driving they would loosen up again. This would be evident when I hit the brakes I would hear the front axle "clunk" both right and left. So what would be causing the u bolts to loosen up? This is getting old and frustrating.. Any ideas ???