Defective release bearing: specialized knowledge helps prevent damage

A large number of malfunctions in commercial vehicles can be traced to the influence of defective release bearing systems. These malfunctions also include “capital” failures such as burnt-out clutches or poor separating characteristics. As a result, it is extremely important to precisely check the release system. There are not many maintenance jobs where concentrating on a few details can have such a big effect and save major costs. Our workshop tips will help you spot defective release bearing systems by means of a visual inspection.

Defective release bearing systems cause various symptoms. Three examples should serve to explain the types of damage that can result from a faulty release bearing system:

Fault in the release bearing system – wear:

If the bearing points of the guide sleeve (shown in this picture), the release fork, or the release shaft are worn, this compromises the clutch's ease of movement – the worst case scenario is a total failure.

Worn guide sleeve

Worn guide sleeve Worn guide sleeve

Fault in the release bearing system – eccentricity:

If, as a result of worn components, the release bearing is defective and no longer guided precisely, this also causes an eccentric movement of the diaphragm spring. This, in turn, leads to considerable abrasion in the contact line (pitch) of the pressure plate. The axial position of the diaphragm spring is modified as a consequence and results in an insufficient frictional connection, making the clutch slip.

New (left) and worn (right) pitches compared

New and worn pitches compared New (left) and worn (right) pitches compared

Fault in the release bearing system – wrong positioning:

A release bearing which has been incorrectly positioned during assembly may get stuck in the fork. To begin with, this results in a stiff clutch, the release distance becomes shorter and the clutch is not separated properly. The stuck fork cannot transfer the force of the diaphragm spring effectively. After a short runtime, the clutch will also start slipping.

Characteristics of wrong positioning

Characteristics of wrong positioning Characteristics of wrong positioning

Worn components in the release system

Wear in the release mechanism is one reason for increased pedal force. Particular attention must be paid to the contact surfaces of the release fork, the contact surfaces of the release shaft, and the release fork itself. If these have entered advanced stages of wear (as is shown in the photo with worn guiding sleeve), or are bent, worn or broken, this will have negative consequences on shift performance. Consequences include clutch grab, separating difficulties, or an increasing degree of sluggishness in the clutch. Because there is no load on the release system, manual testing of release shaft operation is not effective. Here a visual inspection makes better sense.

ZF Aftermarket products

Clutch part kits

ZF Aftermarket offers clutch parts as complete kits for easy service which come with clutch pressure plate, clutch disk and release bearing. All ZF Aftermarket kits include a matching grease pad with high-performance lubricant for one-time, professional greasing of the hub splines during installation.

Release forks for commercial vehicles

Clutch release forks for commercial vehicles are also new additions to the product range. ZF Aftermarket delivers them as one ready-to-install set.