The gearbox bearing is an essential part of your vehicle's transmission system. It ensures the rotational movement transmitted by the engine. Over time, it can wear out, requiring rapid replacement to avoid major vehicle malfunctions.

What are gearbox bearings ?

Gearbox bearings maintain the rotational movement transmitted by your car's engine. They are installed at the ends of the primary and secondary transmission shafts and comprise several components :

• Inner ring : Attached to the gearbox shaft, it rotates with the shaft and plays a crucial role in the rotational movement.
• Outer ring : Attached to the gearbox housing, it remains stationary.
• rolling elements (rollers or balls) : Placed between the inner and outer rings, these elements facilitate rotation of the inner ring as well as the shaft, reducing friction.
• Cage (or separator) : Holds the rollers or balls equidistant from each other and guides them correctly, ensuring even load distribution and smooth rotation.

Gearbox bearings thus ensure smooth rotary motion of the drive shafts, guaranteeing efficient and reliable transmission of engine power to the vehicle's wheels.

In general, a gearbox contains four main bearings :

1. Primary shaft bearing : located at the end of the primary shaft, it supports the input of rotary motion.
2. Secondary shaft bearing : Located at the end of the secondary shaft, it supports the output of rotary motion to the wheels.
3. Countershaft bearing : This bearing supports the countershaft, which transmits rotation between the primary and secondary shafts. The countershaft plays a crucial role in gear shifting.
4. Differential bearing : supports the differential, a key component of the gearbox (often located in transaxle transmissions) which allows the wheels to turn at different speeds when cornering.

What are the different types of gearbox bearings ?

Gearbox bearings vary according to the gearbox model, but the most common types are :

• Tapered bearings : Consisting of a cone (the part with the rollers) and a cup (the outer ring which acts as a raceway for the rollers). They are often used to support combined loads (radial and axial) and are typically installed in applications where axial forces are significant, such as intermediate and differential shafts.
• Straight ball bearings : This classic bearing design features a single row of balls. They are mainly used to support radial loads and are often installed on primary and secondary shafts where axial forces are less significant.
• Cylindrical roller bearings : Used to support high radial loads, these bearings are often installed in applications where radial forces are predominant, such as intermediate shafts.
• Needle roller bearings : Used for their high load capacity, small size, precision and resistance to wear. They play a crucial role in maintaining the efficiency and reliability of transmission systems.

How can I tell if a gearbox bearing is worn ?

Detecting wear in a gearbox bearing is not always easy. However, certain noises can indicate a problem, such as rattling, grinding or whistling. Although the gearbox may continue to operate normally, these noises should not be ignored.

To identify a fault, proceed as follows :

1. Start the engine and drive for a few kilometers : Warm up the gearbox by running the engine at around 4,000 rpm while engaging the clutch, without engaging a gear.
2. Depress the clutch pedal and switch off the engine at the same time : if you hear a clicking sound that changes as the gearbox input shaft speed drops, the bearings are probably damaged.

As friction increases, the bearings heat up, preventing gear engagement. Damage is often most noticeable in 5th gear. Act quickly to avoid irreparable gearbox damage.

Conclusion

To sum up, gearbox bearings play a crucial role in the operation of your vehicle. Their wear can lead to major problems, which is why it's so important to monitor them and replace them at the first sign of failure.