The Bilstein B6 24-278638 is a rear monotube shock absorber for the 2015-2018 Subaru Outback, intended to replace the factory rear damper. It uses a velocity-sensitive digressive piston that changes its resistance as road input changes, which is the basis for Bilstein's fade-resistant damping claims. For an Outback owner who notices the rear end feeling loose or floaty after long highway runs or repeated bumps, that steadier damping is the main reason to choose this part over a generic replacement. Monotube construction places the working oil and gas in a single tube, which is the design Bilstein relies on for consistent damping under heavy use.
Fitment is the first thing to verify. Listings for this part do not agree on which trims and drivetrains the rear pair covers, so confirm your exact year, trim, and AWD status with the manufacturer before ordering. Plan the swap around the manufacturer's installation instructions, which govern torque values and tightening sequence, and support the vehicle on proper jack stands before working under it. Searching for "Bilstein B6 24-278638 rear shock," "2015-2018 Outback rear monotube shock upgrade," or "digressive piston rear damper Subaru" will bring up the correct application details.
