784C, 785C and 785C HAA Off-Highway Truck/Tractors Power Train Caterpillar


Rear Axle and Final Drive System

Usage:

785C 1HW



Illustration 1g00498627

Schematic for the Rear Axle Hydraulic System




Illustration 2g00470567

(1) Flow control valve

(2) Cooling fan (attachment)

(3) Rear axle power train filter

(4) Port for the pressure sensor of the rear axle hydraulic system

(5) Relief and temperature control valve

(6) Rear axle oil flow control and relief valve

(7) Rear wheel

(8) Fiberglass shroud

(9) Rear axle oil gear pump

(10) Rear axle housing

(11) Differential and bevel gear

(12) Suction screen

(13) Bypass line for the filter

(14) Port for the temperature sensor of the rear axle hydraulic system

Operation of the Rear Axle Hydraulic System

This hydraulic system lubricates the bearings for the differential and bevel gear and the bearings for the rear wheels. This hydraulic system also cools the bearings for the differential and bevel gear and the bearings for the rear wheels. This hydraulic system is independent from the other hydraulic systems. For the correct oil that should be used in the system, refer to the Operation and Maintenance Manual for your machine. During long hauls, fiberglass shroud (8) reduces the temperature of the rear axle by reducing the amount of oil that is agitated by the bevel gear.

Rear axle oil gear pump (9) pulls oil from the bottom of rear axle housing (10) through suction screen (12). This oil flows to the rear axle oil flow control and relief valve (6). Rear axle oil flow control and relief valve (6) is located on the top of the rear axle housing. The pressure sensor for the rear axle hydraulic system is located in port (4) in rear axle oil flow control and relief valve (6). The oil temperature sensor for the rear axle hydraulic system is located in port (14) in rear axle oil flow control and relief valve (6). The oil temperature sensor and the pressure sensor for the rear axle hydraulic system will send input signals to the Vital Information Management System (VIMS).

The oil enters rear axle flow control and relief valve (6). When the oil temperature is below 43.3°C (110°F), relief and temperature control valve (5) will be open. The oil will flow into rear axle housing (10). If the oil temperature is above 43.3°C (110°F), the temperature element will expand and relief and temperature control valve (5) will close. All the oil will flow to the power train filter (3). If the pressure of the oil achieves a level of 620 kPa (90 psi), the oil pressure compresses the spring in relief and temperature control valve (5). This opens relief and temperature control valve (5) and the oil flows into rear axle housing (10) .

The oil enters rear axle power train filter (3). Rear axle power train filter (3) has a filter bypass switch in case of restriction. The filter bypass switch sends input signals to the VIMS. If rear axle power train filter (3) is restricted, oil will be returned to the rear axle housing (10) through bypass line (13). The oil that passes through rear axle power train filter (3) flows through cooling fan (2), if the cooling fan is equipped. The oil then flows to flow control valve (1) .

Flow control valve (1) sends the oil flow to the bearings in rear wheels (7). Flow control valve (1) also sends the oil flow to the bearings of the differential and bevel gear (11). At high ground speeds, the excess flow is diverted to the axle housing in order to prevent overfilling the final drives.

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