3.90 8.5in 10 Bolt GM

The 3.90 8.5in 10 Bolt GM ring and pinion gear set from Richmond is an essential upgrade for street performance, drag racing, and heavy-duty towing applications where gear ratio optimization directly impacts acceleration, torque delivery, and engine efficiency. This gear set is ideal for builders and mechanics upgrading General Motors 8.5-inch 10-bolt differentials who demand precise gear meshing and predictable power transfer under load.

Manufactured to OEM tolerances using premium nodular iron and hardened steel, Richmond gear sets ensure that ring and pinion teeth resist scoring, pitting, and fatigue wear even under sustained boost or repeated launch loads. The 3.90 ratio multiplies engine torque at the wheels, reducing RPM drop during acceleration while keeping engine speed manageable during highway driving—a critical balance for daily-driven performance cars.

Proper gear oil lubrication and break-in procedures are essential; Richmond recommends using their friction-modifier additive package and running the gears under controlled load before full throttle engagement. The compact 8.5-inch housing fits OEM GM differentials, making installation straightforward for experienced technicians using a quality press and seal kit.