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| Specification | Details |
|---|---|
| Brand | ARB |
| Manufacturer part number | RD139 |
| SKU | XADLRD139 |
| Differential / axle | AAM 11.5-inch rear |
| Vehicle application | Matching AAM 11.5-inch rear axle in listed Dodge/Ram and Chevrolet/GMC HD applications |
| Axle shafts | 30 spline |
| Gear ratio | All supported ratios |
| Operation | Selectable, air-operated locking; open differential when disengaged |
| Ring-gear outside diameter | 292.1mm [11.5 in] |
| Ring-gear inside diameter | 187.2mm [7.37 in] |
| Ring-gear mounting | 12 bolts on diameter 220.0mm [8.66 in] |
| Ring-gear bolt torque | 237 Nm; professional setup value |
| Backlash | 0.12-0.18 mm; professional setup value |
| Bearing-cap torque | 280 Nm; professional setup value |
| Carrier bearings | Not supplied in the ARB parts list; installation bearings selected separately |
| Air supply | CKMA12 single can operate one or two Air Lockers; compatible compressor purchased separately |
| Twin compressor option | CKMTA12: higher-flow tyre inflation; separate 171503 manifold for Air Locker connections |
Give your heavy-duty truck more grip when you need it
A heavy-duty truck earns its keep on awkward ground as well as on the road. The RD139 gives the matching AAM 11.5-inch rear axle selectable locking, helping both rear wheels contribute when one would otherwise spin. It combines that off-road traction with normal differential action when disengaged.
SKU: XADLRD139
An open differential allows the wheels to turn at different speeds, which is useful for corners. On uneven ground, however, one wheel can spin while the other has grip available. Engaging the Air Locker locks the differential so both wheels turn at the same speed. That helps you make more use of the grip available on the axle.
RD139 matches the AAM 11.5-inch, 30-spline rear differential with a 12-bolt ring-gear mounting pattern. The 11.5-inch axle identity matters: this is a different differential from the smaller AAM and GM axle models, even where the trucks look similar.
Disengaged, the Air Locker behaves as an open differential. You can enjoy normal road driving, then select locking for a low-traction off-road section. Engage it before the wheels are spinning, use it where the tyres can slip, and disengage it when turning or a firmer surface calls for normal differential action.
The ARB CKMA12 single onboard compressor can operate one or two Air Lockers, so it is a straightforward choice for a front-and-rear locker setup. It also supports tyre inflation with the appropriate hose kit. The compressor is purchased separately.
If you regularly air down for off-road driving, the ARB CKMTA12 twin onboard compressor is a worthwhile upgrade. Its higher airflow gets your tyres inflated faster, which is especially useful with larger tyres or when you are inflating several in a row. To connect Air Lockers to the twin, add the separate ARB 171503 compressor manifold kit. The ARB pump-up kit supplies the tyre-inflation hose and accessories.
A differential specialist sets bearing preload, ring-and-pinion backlash, air sealing and line routing during installation. Accurate setup matters for quiet running, reliable engagement and the life of the axle. Bearings, seals and installation parts must match this differential.
For UK customers, prices include VAT, customs and delivery unless checkout states otherwise. For customers outside the UK, local customs and taxes remain your responsibility, and shipping is shown at checkout. If a shipping option is not available, email us and we will prepare a tailored quote.
Many of the products we sell are made to order, imported or custom built, so a lead time may apply. If you need a part urgently, contact us before ordering and we will confirm the expected delivery timeframe and process.
Both wheels on that axle turn at the same speed, helping you use the grip available when one wheel would otherwise spin. It is especially useful for low-traction off-road sections.
It operates as an open differential, allowing the wheels to turn at different speeds for normal cornering.
The compressor is sold separately. The ARB CKMA12 single onboard compressor can operate one or two Air Lockers.
RD139 matches the AAM 11.5-inch, 30-spline rear differential with a 12-bolt ring-gear mounting pattern. The 11.5-inch axle identity matters: this is a different differential from the smaller AAM and GM axle models, even where the trucks look similar.
Installation includes differential setup, bearing selection, backlash adjustment and air sealing. We recommend a differential specialist so the locker and the existing gearset are set up together.
The CKMA12 single can operate a front and rear Air Locker. Choose the CKMTA12 twin if you also want higher airflow for regular tyre inflation. The twin needs the separate 171503 manifold for Air Locker connections; tyre inflation uses the appropriate hose kit.
Model year, engine, drivetrain, hardware and existing modifications can all change what fits. Check the applications and supplier notes above, or send us your exact vehicle and setup before ordering.
Send us your vehicle, year, current setup and any fitting date, event, trip or deadline before ordering. We will help check fitment, product choice and timing.
