Viscous Limited Slip Differential. Transmission case will have a 5" ish bulge by the driver’s side half shaft. The only way to determine if it is properly working is put the car in 1st gear, bring the rpm’s up to 5000, pay out the clutch quickly and depress the gas fully. If it lays down two 50 foot long streaks then it has a functioning VLSD. One wheel peel no VLSD.