Troubleshooting Guides Understand, diagnose, and repair those mysterious 4-wheel drive front axle issues. This guide explains how the OEM units function, what causes them to fail, and which corrections are available. PDF Instruction Downloads Complete Troubleshooting guide PDFChevrolet/GMC K Series PDFChevrolet/GMC S Series PDFDodge PDFJeep PDFFord PDFPSL1100 Perm-Lok PDF Helpful Resources Chevy/GMC K SeriesChevy/GMC S SeriesDodgeJeep