Automatic locking differential designed for 1957 through 1987 Ford cars, trucks, and vans with 31spline axles and a 9 inch ring gear. Compatible with all gear ratios except 2.72. Key benefits Improved traction: Locks under torque to send power to both wheels, reducing wheel spin on slippery or uneven surfaces. Simple, reliable operation: Mechanical automatic locker requires no wiring or electronics and engages only when needed. Broad vintage Ford fitment: Direct fit for 9 inch ring gear housings with 31spline axle shafts from 1957 to 1987, making it suitable for restorations and upgrades. Durable design: Precisionmachined components engineered to withstand repeated use and heavy loads in daily driving, towing, and light offroad work. Clear compatibility note: Fits all gear ratios except 2.72. Confirm axle spline count and ring gear diameter before . Important specifications Vehicle fitment: 19571987 Ford cars, trucks, and vans Axle spline count: 31 spline Ring gear diameter: 9 inch Gear ratio compatibility: Compatible with all ratios except 2.72 Function: Automatic locking differential for improved traction under load Practical use scenarios Restored 1960s or 1970s Ford pickup used for weekend trail runs and occasional work duty where extra traction is required during hauling or uneven terrain. Classic Ford street rod upgraded with modern tires that may break traction under hard acceleration; locker helps transfer torque to the wheel with traction. Older Ford delivery or service van operating in winter conditions where wheel slip on snow and ice reduces control and efficiency. Why choose this differential Designed specifically for late vintage Ford 9 inch rear axle applications with 31spline axles, so fitment is straightforward for compatible housings. Offers a mechanical, maintenancefriendly solution to traction loss without the complexity of electronic systems. Provides predictable locking behavior under torque and allows differentiation when freewheeling or turning for drivability. Fitment reminder Verify axle spline count is 31 spline and ring gear is 9 inch. Not compatible with 2.72 gear ratio setups. This differential is intended to or upgrade the carrier in compatible Ford 9 inch rear axle housings from 1957 through 1987 to improve traction and load transfer performance.