See Figures 1, 2, 3 and 4
The drive axle is said to have a certain axle ratio. This number (usually a whole number and a decimal fraction) is actually a comparison of the number of gear teeth on the ring gear and the pinion gear. For example, a 4.11 rear means that theoretically, there are 4.11 teeth on the ring gear and one tooth on the pinion gear or, put another way, the driveshaft must turn 4.11 times to turn the wheels once. Actually, on a 4.11 rear, there might be 37 teeth on the ring gear and 9 teeth on the pinion gear. By dividing the number of teeth on the pinion gear into the number of teeth on the ring gear, the numerical axle ratio (4.11) is obtained. This also provides a good method of ascertaining exactly what axle ratio one is dealing with.
Another method of determining gear ratio is to jack up and support the car so that both rear wheels are off the ground. Make a chalk mark on the rear wheel and the driveshaft. Put the transmission in neutral. Turn the rear wheel one complete turn and count the number of turns that the driveshaft makes. The number of turns that the driveshaft makes in one complete revolution of the rear wheel is an approximation of the rear axle ratio.
All 1970-87 Volvos use a solid rear axle housing carried in two support arms. Two torque rods, connected between the axle shaft tubes and the body, limit the rear axle wind-up. A track bar (Panhard rod) controls lateral movement of the axle housing. The 760GLE also incorporates a triangulated dual-ladder sub-frame to connect the axle unit to the uni-body.
In 1988, the 760 4 door sedan and the 780 model introduced Volvo's Multi-link suspension system. This independently suspends each rear wheel, allowing improved ride and road-holding as well as allowing each rear wheel to be aligned separately.
Final drive is of the hypoid design, with the drive pinion lying below the ring gear. On the solid axle models, each axle shaft is indexed into a splined sleeve for the differential side gears, and supported at its outer end in a tapered roller bearing. Bearing clearance is not adjustable by use of shims as on earlier model Volvos, but instead is determined by bearing thickness. Both sides of the axle bearings are protected by oil seals.
On vehicles with the Multi-link suspension, the axles are actually halfshafts, bolted to the differential. Each halfshaft has a constant velocity (CV) joint at each end, allowing a full range of motion as the car passes over bumps and depressions.
Some special 1976 and later models are equipped with limited slip differentials for better traction.
The identification plate showing the final drive ratio, the part number and the serial number of the differential can be found on a plate attached to the axle tube or the housing.