This document describes the ARB Air Operated Locking Differential, model RD136, designed for Nissan H233B, 31 spline axles. This device is an air-operated locking differential that, when engaged, locks the two axle shafts together, forcing both wheels to rotate at the same speed. This provides maximum traction in off-road conditions where one wheel might otherwise lose traction and spin freely.
Function Description
The ARB Air Locker is an air-operated locking differential that replaces the standard open differential in a vehicle's axle. When activated by compressed air, a locking mechanism engages, effectively coupling the two axle shafts. This ensures that both wheels on that axle receive equal power, regardless of traction conditions, preventing wheel spin on one side while the other remains stationary. When disengaged, the Air Locker functions as a conventional open differential, allowing for normal on-road driving and cornering.
The system requires an external air source, typically an ARB Air Compressor, to supply compressed air to a solenoid valve. The solenoid, controlled by an actuator switch inside the vehicle, directs air pressure to the differential, engaging the locking mechanism. The installation process involves removing the existing differential, installing the Air Locker, drilling and tapping a bulkhead port in the differential housing for the air line, connecting the air line, and wiring the actuator switch to the air compressor.
Important Technical Specifications
- Model: RD136
- Application: Nissan H233B, 31 Spline
- Axle Spline: 31 tooth, Ø32mm [1.26"]
- Ratio Supported: All
- Ring Gear ID: 146.0mm [5.75"]
- Ring Gear Bolt Size: 12mm
- Ring Gear Bolts: 9 bolts on Ø176mm [6.93"]
- Ring Gear Torque: 142Nm [105 ft-lb]
- Backlash: 0.15-0.20mm [0.006-0.008"]
- Bearing Cap Torque: 99Nm [73 ft-lb]
- Operating Air Pressure: Minimum 586 kPa [85 PSI] for actuation. Bench testing is performed at 620kPa [90 PSI].
- Carrier Bearings: The Air Locker is designed to use higher-rated 50mm carrier bearings (Timken # 32010X-32010X, ARB # 160116) instead of the OE Nissan 45mm carrier bearings. Original bearings are not reusable.
- Ring Gear Bolts: Two different bolt lengths were used on this model of Nissan differential. The Air Locker is designed to use 31.5mm [1.24"] bolts (Nissan part # 3810212S00). If longer bolts (e.g., 36mm [1.42"]) are present, spacers (supplied) must be used under the bolt heads to prevent the threads from bottoming out.
- Bulkhead Fitting: Requires an 11.2mm [7/16"] diameter hole drilled and tapped with a ¼"NPT thread tap.
- Air Line: 6mm diameter nylon tubing.
- Solenoid Porting: 1/8" BSP.
Usage Features
- On-Demand Traction: The Air Locker provides selectable traction, allowing the driver to engage the locking mechanism only when needed for off-road conditions and disengage it for normal on-road driving.
- Actuator Switch: The system is controlled by an actuator switch mounted within the vehicle, allowing the driver to easily engage or disengage the differential lock. The switch illuminates to indicate when the Air Locker is engaged.
- Safety Considerations:
- The actuator switch should be mounted within operator reach but away from accidental engagement.
- The Air Locker should only be engaged when off-road and in situations requiring maximum traction.
- It is critical to set up bearing pre-load correctly during installation to prevent undue bearing wear, increased stresses, running noise, and gear damage.
- The seal housing tube must be profiled to ensure it does not interfere with bearing caps, the Air Locker, ring gear, or axle housing, maintaining at least 8mm (5/16") clearance.
- The seal housing must float and self-center on the bearing journal without pulling against the seal housing.
- When installing the axle, care must be taken not to damage the axle shaft oil seals.
- Air System Compatibility: While ARB recommends using a genuine ARB Air Compressor for optimal performance and reliability, the Air Locker can be operated with alternate air sources that meet specific criteria:
- Minimum supply of 586 kPa [85 PSI].
- Sufficient tank capacity to actuate the Air Locker(s) in one charge without regeneration.
- Supply of clean air, free of rust, dirt, water, or other foreign matter.
- Matching 1/8" BSP porting for the Air Locker solenoid.
- Solenoid mounted in close proximity to the air supply, secured from vibration and shock.
Maintenance Features
- Pre-Installation Inspection: Before installation, it is crucial to check for metal particles in the existing differential oil and housing, which may indicate worn bearings or differential components. ARB strongly recommends inspecting the axle assembly for concentricity and straightness, especially if the vehicle has experienced collision damage or heavy off-road use, as misalignment can lead to excessive wear or failure of the differential and axle shafts.
- Bearing Replacement: The Air Locker requires higher-rated 50mm carrier bearings (Timken # 32010X-32010X, ARB # 160116) as the original 45mm Nissan bearings are not reusable.
- Seal Housing O-rings: During installation, ensure the seal housing O-rings are clean and free from contaminants. Generously lubricate the O-rings with oil prior to assembly to prevent twisting and ensure proper sealing, which prevents excessive wear and leakage.
- Air Line Installation: The air line must be routed and secured carefully to prevent damage from rubbing, kinking, or snagging. Avoid sharp edges and abrasive surfaces. Ensure sufficient slack for suspension travel.
- Leak Testing: After installation, the air system must be thoroughly leak tested. This involves charging the system with air pressure (620 kPa [90 PSI]), shutting off the valve, and observing for any pressure drop. A soap and water mixture can be sprayed onto fittings and the seal housing to identify leak points by observing bubbles. Leaky fittings should be tightened, or disassembled, cleaned, and re-sealed with thread sealant. If the seal housing leaks, it should be carefully removed and refitted, checking O-rings for damage.
- Differential Fluid: The differential must be refilled with the correct lubricant according to ARB recommendations (refer to the ARB Air Locker Operating & Service Manual). The oil level should be checked and topped up after rotating the differential center two full turns. Thread sealant should be applied to the filler plug.
- Post-Installation Checklist: A comprehensive checklist is provided to ensure all critical steps, including leak testing, proper torque settings, fluid levels, secure wiring and air lines, and correct switch function, are completed.
- User Education: All operators using the Air Locker should read and fully understand the ARB Air Locker Operating & Service Manual. A warning sticker should be placed near the actuator switch(es).
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