This maintenance manual provides detailed instructions for the service and repair of Rockwell Double-Reduction Drive Units, specifically front-mounted models. These units utilize a two-stage reduction process—a primary spiral bevel or hypoid gear set followed by a secondary helical gear set—to provide high torque for heavy-duty applications.

1. Key Technical Specifications

Accurate assembly requires adhering to precise adjustment parameters to ensure component longevity:

Pinion Bearing Preload: Controlled by the thickness of the spacer between bearings. For new bearings, the preload should be 15–25 lb-in (1.7–2.8 N·m); for used bearings in good condition, it is 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). This can also be measured by expansion between bearing caps: 0.002–0.009 inch (0.05–0.229 mm) for most models, and 0.006–0.013 inch (0.15–0.33 mm) for larger 180 series models.
Ring Gear Backlash: For gears with a pitch diameter of 17 inches or larger, the range is 0.010–0.020 inch (0.25–0.51 mm), with a nominal setting of 0.015 inch (0.38 mm) for new gear sets.
Runout and Resistance: Maximum allowable ring gear runout is 0.008 inch (0.20 mm). The maximum rotating resistance for differential gears is 50 lb-ft (68 N·m) applied to one side gear.

2. Core Maintenance and Assembly

Matched Gear Sets: Drive pinions and ring gears are matched sets and must always be replaced together.
Pinion Depth Adjustment: 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 gears.
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 permit 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. Safety and Operational Guidelines

Driver-Controlled Main Differential Lock (DCDL): Before removing or installing a carrier equipped with a DCDL, the 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: To prevent internal damage, axle shafts must be removed before towing the vehicle with its drive wheels on the ground.
Lubrication: Use only API GL-5 hypoid gear oil. Sump temperatures must never exceed 250°F (121°C).