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Not sure which one? Ask us to confirm fitment first →For UK customers, prices include VAT, customs and delivery unless checkout states otherwise. Outside the UK, shipping is shown at checkout and local customs and taxes remain your responsibility.
Some products are made to order, imported or custom built. If timing matters, contact us before ordering and we will confirm the expected delivery timeframe.
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| Specification | Details |
|---|---|
| Brand | ARB |
| Manufacturer part number | RD138 |
| SKU | XADLRD138 |
| Differential / axle | Land Rover P38A, 205 mm carrier flange |
| Vehicle application | Matching Range Rover P38 / Defender / Discovery 2 P38A axles |
| Axle shafts | 24 spline |
| Gear ratio | 3.54:1; 4.7:1 requires the specified spacer and longer bolts |
| Operation | Selectable air-operated locking; open differential when disengaged |
| Supplied unit | One Air Locker differential assembly |
| Carrier bearings | Carrier bearings are selected separately to suit the axle and adjusters. |
| Ring-gear inside diameter | 125.4 mm |
| Ring-gear mounting | 10 bolts on 142 mm bolt circle |
| Carrier-flange diameter | 205 mm |
| Air supply | Compatible onboard air supply required; compressor purchased separately |
Give your P38A axle selectable off-road traction
The RD138 gives your matching 24-spline P38A differential selectable locking for the sections where one wheel loses grip. Both wheels can turn together when engaged, then return to normal differential action when switched off. It is the larger, 205 mm-flange Land Rover carrier.
SKU: XADLRD138
On uneven ground, an open differential can let one wheel spin while the other has grip available. Engaging the Air Locker makes both wheels on that axle turn at the same speed, helping you tackle the section with controlled progress. Tyres and terrain still determine the grip available; the locker helps you use it.
RD138 fits the P38A carrier with a 205 mm flange, rather than the 174 mm Rover-type carrier used by RD128. Match the differential type in your Range Rover P38, Defender or Discovery 2. Standard 3.54:1 gears are supported; early 4.7:1 gears need the RD03A 5 mm spacer and specified longer bolts. North American Discovery models use the Rover-type axle application instead.
Disengaged, it operates as an open differential so the wheels can turn at different speeds in a corner. Engage it before a difficult low-traction section, with the wheels turning at the same speed. Switch it off when normal differential action is needed, particularly on firm surfaces or tight turns.
The ARB CKMA12 single onboard compressor can operate one or two correctly installed Air Lockers. Add the ARB pump-up hose kit if you also want to inflate your tyres with it. The compressor and inflation kit are separate purchases.
If you regularly air down for trails, the ARB CKMTA12 twin onboard compressor offers more airflow for tyre inflation. Its Air Locker connection uses the separate 171503 manifold kit. Choose the twin for the extra inflation capability; the CKMA12 already has capacity for two lockers.
A differential specialist sets the bearing preload, gear backlash and air sealing together, so your locker and existing gearset run correctly. Carrier bearings are selected separately to suit the axle and adjusters. The air line is routed clear of heat and moving parts, then the locking operation is checked before the vehicle returns to use.
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.
When one wheel would otherwise spin, engaging the locker lets both wheels on that axle turn together. That helps the wheel with grip contribute to your progress on loose climbs, ruts and uneven tracks.
Switched off, it works as an open differential for normal cornering. Keep it disengaged on firm surfaces where the tyres cannot slip.
Land Rover P38A, 205 mm carrier flange with 24-spline shafts. The supported ratio is 3.54:1; 4.7:1 requires the specified spacer and longer bolts.
No. The CKMA12 single onboard compressor can operate one or two correctly installed Air Lockers. The CKMTA12 twin is a useful upgrade if you also want more airflow for tyre inflation; use its separate 171503 manifold for locker connections.
One RD138 Air Locker differential assembly. The compressor is separate. Carrier bearings are selected separately to suit the axle and adjusters.
The installation includes bearing preload, gear backlash, air sealing and engagement checks. We recommend a differential specialist so the locker and your gearset are set up together.
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.
