ARB RD99 Air Locker Rear Differential for Ford 9" 35-Spline 3.250" Case

Vehicle Fitment

• Universal fitment for Ford 9" rear axle housings using 35-spline axle shafts and an aftermarket 3.250" bore carrier case

Fitment Notes

• Designed specifically for Ford 9" differentials with 35-spline, 1.50" diameter axle shafts.
• Requires an aftermarket 3.250" bore nodular iron or performance third-member case.
• Does not fit OEM Ford 9" third-member assemblies or 28/31-spline carrier cases.
• Suitable for use in front or rear Ford 9" axle setups where housing and case match these specifications.
• ARB on-board air compressor (such as CKMA12 or CKMTA12) required for locker actuation.

Features

• Air-actuated locking differential provides 100% lock on demand for maximum traction.
• Forged internal components and high-strength case engineered for severe off-road use.
• Operates as an open differential when disengaged for smooth, predictable on-road manners.
• Instant push-button engagement from the cab, allowing precise control over when the axle is locked.
• Compatible with all common Ford 9" ring-and-pinion gear ratios when installed in a 3.250" bore case.
• Sealed air system keeps contaminants out of the locking mechanism for long service life.
• Designed for repeated high-load cycling in rock crawling, desert, mud, and overland environments.
• Backed by ARB's off-road engineering experience and multi-year air locker warranty coverage.

Specifications

• Part Number: RD99
• Differential Type: Air Locker (pneumatically actuated locking differential)
• Axle Type: Ford 9" rear axle
• Spline Count: 35-spline axle shafts
• Shaft Diameter: Approx. 1.50"
• Case Requirement: Aftermarket 3.250" carrier bearing bore third-member
• Gear Ratio Compatibility: All Ford 9" ratios supported by the specified case
• Actuation: 12V air solenoid and compressor-driven air supply

Included Components

• 1x ARB RD99 Air Locker differential assembly
• 1x Air solenoid valve for locker control
• 1x Air line kit with bulkhead fittings and hardware
• 1x Seal housing and associated O-rings
• Installation hardware and setup documentation

Product Description

The ARB RD99 Air Locker is a heavy-duty locking differential engineered for Ford 9" axle applications using 35-spline axle shafts and an aftermarket 3.250" bore carrier case. When activated by an ARB on-board air compressor, the locker mechanically couples both axle shafts together, delivering 100% traction to both wheels for superior control in demanding off-road conditions. When switched off, it functions like a standard open differential to maintain predictable handling on pavement.

Ideal for custom Ford 9" builds, buggies, rock crawlers, and performance trucks, the RD99 is designed to handle high torque loads and aggressive terrain. Its robust forged internals, sealed air actuation system, and compatibility with a wide range of gear ratios make it a versatile solution wherever a properly configured Ford 9" third member is used. By pairing this locker with the correct 3.250" nodular case and 35-spline shafts, builders gain a proven traction aid that can be precisely controlled from the driver's seat for maximum capability on and off the trail.