FWIW, from Wikipedia: " First generation (1997–2002) First generation (UN93) ... Transfer case (4x4 models) 2-speed BorgWarner 4406 High range ratio: 1.00:1 Low range ratio: 2.64:1 ... Expedition was available with automatic full-time ControlTrac four-wheel drive with two-speed dual range BorgWarner 4406 transfer case and a center multi-disc differential. ControlTrac was introduced in 1995 and included four selectable modes: Two High, Auto, Four High (lock) and Four Low (lock). Two High mode and Auto mode with auto-lock was not available." as you can see, on this and many other sites on the internet (https://schematron.org/borg-warner-4406-transfer-case-diagram.html), your transfer case is a chain drive.