This maintenance manual provides technical instructions for the service and repair of Rockwell Tandem Axle Forward-Rear Drive Units, specifically models RT-140, RT-145, RT-160, and RT-180. These units are through-drive assemblies that include an inter-axle differential and a main differential, often equipped with a Driver-Controlled Main Differential Lock (DCDL).

1. Key Technical Specifications

Proper assembly requires adhering to precise adjustment parameters:

Pinion Bearing Preload: Controlled by a spacer between the bearings. New bearings require a preload of 15–25 lb-in (1.7–2.8 N·m), while used bearings in good condition require 5–25 lb-in (1.7–2.8 N·m).
Main Differential Bearing Preload: The standard specification is 15–35 lb-in (1.7–3.9 N·m). It can also be measured by expansion between bearing caps: 0.002–0.009 inch for RT-140/145/160 models and 0.006–0.013 inch for RT-180 models.
Ring Gear Backlash: For new gear sets, backlash should be set to a nominal 0.015 inch (0.38 mm), within a range of 0.010–0.020 inch (0.25–0.51 mm).
Maximum Runout: The maximum allowable lateral runout for the ring gear is 0.008 inch (0.20 mm).

2. Core Assembly Procedures

Matched Sets: Drive pinions and ring gears are matched sets and must always be replaced together.
Pinion Depth Adjustment: The depth is controlled by shims between the bearing cage and carrier. Technicians must calculate new shim thickness based on measurement of the old pack and the Pinion Cone (PC) variation numbers marked on the gear heads.
Ring Gear Installation: Ring gears must be heated in water to 160°F–180°F (71°C–82°C) for 10 to 15 minutes before installation to ensure a press-free fit over the case half pilot.
Unitized Pinion Seals: These must be installed using specific drivers to ensure they are seated squarely against the bearing cage with a gap no larger than 0.010 inch.

3. Lubrication and Maintenance

Fluid Standards: Use only API GL-5 hypoid gear oil.
Operational Temperature: The axle sump temperature must never exceed 250°F (121°C) to avoid damaging internal components.
Change Intervals: For heavy-haul or construction vocations, petroleum-based oil should be changed every 25,000 miles or annually.

4. Safety and Towing

Carrier Removal (DCDL Models): Before removing or installing the carrier, the differential lock must be shifted and held in the engaged (locked) position using a manual engaging capscrew to provide necessary clearance from the axle housing.
Towing Requirements: Axle shafts must be removed before towing the vehicle with its drive wheels on the ground to prevent internal damage.