Original Factory gear for GM 8.5" (no ABS) in a 3.42 ratio. Use Yukon gear for Impala. Two-step - face to flank set-up only. OEM gears are recommended for quiet applications where noise may be an issue. Factory gears are the quietest application available on the market and often come at a higher cost. Factory gears come with a one year warranty against defects.This gear set does not have an ABS provision on the pinion.