Auto propshafts and differentials parts

Propshafts and differentials: key insights into component performance, mounting, diagnostics, and durability

Propshafts and differentials are units intended for torque transmission and distribution between the rear car wheels and axles. The former are responsible for the rotation of the driving wheels. The latter allow the wheels of a single axle revolve at different speeds.

Design of prop shafts and differentials

A prop shaft looks like a hollow tube at the end of which there are U joints with four bearings providing torque transmission at an angle. The prop shaft also has a spline coupling which lets its parts stretch out and allows for the vertical movement of the assembly parts. There is intermediate support, namely an overhung bearing, that is used for a more reliable fixation of the unit. The flex disc is installed to compensate for vibration and angular motion between the driveshaft flanges and the gearbox. If the shaft consists of several sections, the number of intermediate bearings increases.

Differentials are planetary gearboxes with a bevel, spur, or worm gear. They can be installed into the rear or front axle housing, the gearbox and the transfer case. The transverse differential typically has a bevel gear consisting of half axles with pinions and housing called a cup. The main gear is installed on the housing. Its motion operates the housing by which torque transmission is transferred through the pinions to the half axles. When the resistance in one of the wheels increases, the pinions begin to rotate the axle shaft by which torque is transferred to the second wheel. To avoid wheelspin on slippery surfaces there is a lock-out mechanism in the unit. It can consist of clutch or viscous couplings, a worm gear, or a set of friction disks.

Maintenance tips

• Examine flexible couplings, mounting bearings and U joints regularly. If you notice any defects, replace the parts at once.
• You should grease the U and spline joints of the prop shaft every 10,000-15,000 km if this is recommended by the manufacturer. There should be special lubricants for this purpose. Use the exact amount of the lubricant specified in your vehicle maintenance manual. An excessive amount can cause the propeller shaft imbalance.
• When changing the proper shaft parts, you should have it balanced.
• Clean dirt from the joint and check the tightness of the flange bolts and the caps of the needle roller bearings during every technical inspection.
• New differentials need to be broken in. That’s why if you’ve replaced the unit or have a new car, you should avoid hard acceleration or braking and high-speed engine performance during the first 800-1000 km. You shouldn’t travel long distances.
• Replace oil in the gearbox in cars with a mechanical ones every 50,000-60,000 km and every 25,000-30,000 km in vehicles with an automatic transmission.

Malfunction symptoms

Knocking or hammering sounds coming from below appearing immediately after engaging the gearbox indicate a loose prop shaft, wear and tear, or damaged U joints or spline couplings. Constant clanking while driving is also an indicator for the deterioration of the unit’s bearings. Vibrations occur if the prop shaft is deformed, the bearings are worn out, or the fasteners become loose. Noises and rattling that grow louder while cornering as well as oil streaks around the unit indicate malfunctions of the differentials.

Malfunction causes

The lack of lubricant leads to a quick breakdown of cardan joints and bearings, gears and spline couplings. The deformation of seals results in the entry of dirt and moisture into the unit due to which the contacting elements wear out quickly and begin to rust. Aggressive driving causes quick deterioration of U joints, bearings, and other parts of the differential. Overheating is also dangerous for the latter.

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