Description
The ARB Air Locker Differential RD187 is a pneumatically operated locking differential engineered for the AMC Model 20 axle, 29-spline, covering gear ratios of 2.73 and below, in IFS front, IRS rear, and solid rear axle positions — fitting select Jeep CJ5, CJ7, Scrambler, J10, and Wagoneer models from 1976 to 1986, and AM General and Hummer H1 vehicles from 1992 to 2004.
IMPORTANT: RD187 covers gear ratios of 2.73 and below only. For AMC Model 20 axles with a gear ratio of 3.08 and above, the correct part is RD186 — not this unit. Additionally, an air compressor is required for operation and is not included with this kit; it must be purchased separately. Verify your axle designation, differential position, and ring-and-pinion ratio before purchasing.
The ARB Air Locker is a pneumatically actuated locking differential that replaces a conventional open differential carrier with a selectable, on-demand locking unit. When engaged, it prevents the internal differential gears from rotating independently, mechanically tying both axle shafts directly to the ring gear. This delivers 100 percent tractive force to both wheels simultaneously, regardless of surface traction conditions. When the locker is disengaged, the differential reverts to standard open behavior with no change to on-road handling or driveline wear.
The locking mechanism is pneumatically operated: compressed air, supplied through the included solenoid valve and air line, actuates an internal collar that locks the differential gears in place. ARB’s patented “timed” locking mechanism is engineered for high mechanical strength and ultra-fast unlocking response. The steel-reinforced, elastomer-bonded annular seal is rated for extreme climatic temperatures and is designed to maintain a reliable air seal under sustained off-road use. The two-piece carrier design minimizes the total number of moving parts, reducing potential failure points that affect long-term reliability.
The RD187 differential carrier is manufactured from steel and finished in silver. Activation is controlled from inside the cab via the included switch, allowing the driver to lock and unlock the differential at any vehicle speed without leaving the driver’s seat. The kit includes the Air Locker differential unit, activation switch, solenoid valve, air line, and bulkhead fitting — everything needed to complete the installation aside from an air compressor, which must be sourced separately. ARB backs the RD187 with a 5-year warranty.
- Fitment: AMC Model 20 axle — 29-spline, 1.25 in (31.5mm) shaft diameter — gear ratios of 2.73 and below — covers IFS front axle, IRS rear axle, and solid rear axle positions — fits select Jeep CJ5 (1976–1983), CJ7 (1976–1986), Scrambler (1981–1985), J10 (1980–1988), and Wagoneer (1979–1986); AM General Hummer (1992–2001); Hummer H1 (2002–2004). For AMC Model 20 with ratio 3.08 and above, see ARB RD186.
- Pneumatically actuated locking differential — provides 100% traction on demand with zero effect on open-differential behavior when disengaged
- Patented “timed” locking mechanism delivers high-strength engagement and ultra-fast pneumatic unlocking
- Two-piece steel carrier design — minimal moving parts for maximum long-term reliability
- Steel-reinforced, elastomer-bonded annular seal rated for extreme climatic temperature range
- In-cab activation switch allows locking and unlocking at any vehicle speed without exiting the vehicle
- Kit includes: Air Locker differential, activation switch, solenoid valve, air line (6mm dia x 6m), and bulkhead fitting (banjo type)
- Air compressor required for operation — sold separately; alternate air source must supply minimum 85 PSI
- Replacement carrier bearing: Timken LM102949 / LM102910
- 5-year warranty
- Sold individually
| Part Number | RD187 |
| Axle | AMC Model 20 |
| Spline Count | 29 tooth |
| Shaft Diameter | 31.5mm [1.24 in] |
| Ratio Supported | 2.73 and below |
| Positions Covered | IFS Front, IRS Rear, Solid Rear |
| Ring Gear OD | 225.6mm [8.88 in] |
| Ring Gear ID | 136.6mm [5.38 in] |
| Ring Gear Bolts | 8 bolts on 165.00mm [6.49 in] bolt circle |
| Ring Gear Torque | 101 Nm [75 ft-lb] |
| Bearing Cap Torque | 101 Nm [75 ft-lb] |
| Backlash | 0.15–0.25mm [0.006–0.010 in] |
| Replacement Bearing | Timken LM102949 / LM102910 |
| Material | Steel |
| Color / Finish | Silver |
| Activation | Pneumatic (air compressor required, sold separately; minimum 85 PSI) |
| Kit Contents | Air Locker differential, activation switch, solenoid valve (12V), air line (6mm x 6m), bulkhead fitting (banjo type) |
| Warranty | 5 Years |
Fitment Information
The RD187 is designed for the AMC Model 20 axle in 29-spline, 1.25 in shaft configurations with gear ratios of 2.73 and below, covering IFS front, IRS rear, and solid rear axle positions. Covered vehicles include select Jeep CJ5 (1976–1983), CJ7 (1976–1986), Scrambler (1981–1985), J10 (1980–1988), and Wagoneer (1979–1986), as well as AM General Hummer (1992–2001) and Hummer H1 (2002–2004). This unit does not cover ratios of 3.08 and above — buyers with an AMC Model 20 axle and a 3.08 or numerically higher gear ratio should refer to ARB RD186. Confirm your specific axle designation, differential position, and ring-and-pinion ratio before purchasing.