What is the rear axle and how it works

The rear axle is often referred to as a beam or subframe, or transmission gearbox. What it is, how it looks, and how it works - read on.

 What is the rear axle

The rear axle is to make a car that combines two wheels on one axle, wheels with suspension and a suspension with a body. In the case of rear-wheel drive, the transmission gearbox assembly is called the axle. 

Rear Axle Functions

The unit serves to perform several functions:

• torque transmission. Differential rear axle increases torque due to downshift. Also, the bridge can change the plane of rotation of the drive wheels, allowing you to rotate the wheels perpendicular to the body when the crankshaft rotates along the axis of the car;
• rotation of driving wheels with different angular speeds. This effect is achieved through the use of a differential (auxiliary satellites), which redistributes the torque depending on the load on the wheel. This makes it possible to safely take turns, especially at high speeds, and the presence of a differential lock allows you to overcome difficult areas when slipping one wheel;
• support for wheels and body. For example, for VAZ 2101-2123 and GAZ Volga cars, the rear axle is of a closed type, in the body of which (stocking) there is a axle and axle gearbox, as well as brake drums. In this case, the suspension is dependent.

On more modern cars, the classic axle provides high cross-country ability due to the long suspension travel, torsional rigidity, as well as a smooth ride, for example, as in the Toyota Land Cruiser 200 SUV.

The device and design of the rear axle in a car

Elements of the classic rear axle:

• a crankcase (stocking), usually one-piece, having a lid in the middle for access to the differential at the rear. On UAZ vehicles, the housing consists of two parts;
• drive and driven gear of the main pair;
• differential case (axle gearbox is assembled in it);
• semiaxial gears (satellites);
• a set of bearings (pinion gear and differential) with a spacer;
• set of shims and gaskets.

The principle of operation of the rear axle. When the car is moving in a straight line, torque is transmitted through the driveshaft to the drive gear of the gearbox. The driven gear rotates at the expense of the leading one, and satellites evenly spin from it (but not around its axis), distributing the moment to the 50:50 wheels. 

When turning a car on one axis, it is necessary to rotate at a lower speed due to the rotation of the satellites around its axis, to a lesser extent, the torque is supplied to the unloaded wheel. This ensures safety and the absence of rolls when turning, exit from the track of movement and less wear of rubber.

Differentials are divided into several types, each of which performs the same work, but carry it out in different ways. There are disk, screw, limited slip differentials, with hard locking. All this provides a high cross, therefore it is used on crossovers and SUVs. 

How to service the rear axle. Maintenance of the axle requires periodic replacement of gear oil. Due to the use of hypoid transmission, the oil poured into the gearbox must comply with the GL-5 classification. Once every 200-250 thousand, you will need to adjust the contact spot between the driven and pinion gears, as well as the bearings. With proper care of the bearings, satellites and distance washer, at least 300 km is enough. 

Types of rear axles assembly

Today, there are three types of rear axle assembly, differing in the type of wheel and axle support:

• semi-unloaded axles;
• fully unloaded axles;
• independent suspension.

Half-axle axle axlesecures them with C-clamps in the crankcase. The axle shaft is fixed with a spline part in the differential box, and on the wheel side it is supported by a roller bearing. To ensure the tightness of the bridge, an oil seal is installed in front of the bearing.

Rear axle with unloaded axles differs in that it transmits torque to the wheel, but does not accept lateral loads in the form of the mass of the car. Such half shafts are often used on trucks and SUVs, they are characterized by high load capacity, however, they have the disadvantage of a larger mass and complex design.

Independent axle rear axle - here the axle shaft has an external and internal hinge of equal angular velocities, while the role of a stop for the body is performed by an independent suspension unit, consisting of at least 3 levers on one side. Such axles have camber and toe adjustment rods, have a wide range of suspension travel, as well as ease of repair of the rear axle gearbox due to the simple design of its attachment to the subframe.

Questions and answers:

What are the bridges by car? There is a continuous (used in cars with dependent suspension), split (wheels are mounted on an independent suspension) and portal (used in cars with multi-link suspension with increasing ground clearance) bridge.

What are car bridges used for? This unit connects the drive wheels and secures them to the suspension. It receives and transmits torque to the wheels.

What is the rear axle for? It is used in rear- and four-wheel drive vehicles. It connects the axle wheels. It provides the transmission of torque to the wheels using a propeller shaft (comes from the transfer case) and a differential (allows the wheels to rotate independently in turns).