The Bilstein B6 4600 rear shock (part 24-186209) is a monotube, gas-pressure damper built for the rear axle of the 2004 Chevrolet Colorado Z85 LS. The manufacturer positions the B6 4600 as a direct-fit replacement for OE shocks on stock-height light trucks and SUVs, and it tunes each part number to its application. A velocity-sensitive digressive piston responds to changing road input, so the rear end keeps its composure over washboard, broken pavement, and loaded-bed driving without changing the factory springs.
Why choose this over a generic stock-style replacement? Its single-tube design dissipates heat more effectively than a standard twin-tube unit, which helps it hold damping force on long grades or when towing. The manufacturer also reports that the B6 line is tested to 240 hours of salt-spray endurance, and the shaft is induction-hardened chrome for seal life. Owners on user forums generally describe a noticeably firmer, more controlled rear end without the harshness they expected. Search terms this part matches include Colorado Z85 LS rear shock upgrade, B6 4600 monotube rear shock, gas-pressure shock for 2004 Colorado, and Bilstein Colorado rear shock replacement.
The manufacturer states that the B6 line is designed to replace the original dampers and pair directly with the factory springs, so a spring change is not required for a stock-height truck.
The manufacturer's fitment lookup should be checked against your VIN and trim before ordering. Owners on user forums recommend matching the rear unit's mount style to your existing shock, since the lower eye and upper pin must line up with the factory brackets.
This is a manageable driveway job for a mechanically inclined owner with a floor jack, two jack stands, a socket set, penetrating oil, and a flat-blade screwdriver or pry bar. Owners on user forums who have swapped B6 rear units on other trucks report that the hardest step is seating the lower eye, which often needs the shock compressed with a jack to align with the mount. Spraying the bolts with penetrating oil well ahead of time helps with rusted fasteners. Several owners also recommend lubricating the bushings and sleeves with silicone or white grease to prevent squeaks and ease alignment, and removing a few wheel-well liner screws improves access to the upper nut. Torque values were not confirmed from the manufacturer's documentation during research, so check the manufacturer's install sheet before final tightening.
