The forklift universal joint transmission is primarily used when the two shafts are not aligned, allowing power to be transferred between them as their relative positions change during operation. This system is commonly found in heavy-duty forklifts such as the CPCD50 and 5CQN, where it connects the transmission to the drive axle and links the engine to the oil pump. The universal joint assembly typically includes a universal joint fork, a cross shaft, and other related components. Its main function is to transfer power from the transmission to the final reducer.
Because the drive shaft must handle high torque, high-speed rotation, and heavy loads, even though its structure isn't overly complex, the technical requirements are quite demanding. Any issues—such as misalignment, poor lubrication, or wear—can lead to shaking, unusual noises, disconnection, or even shaft failure. Therefore, regular and careful maintenance of the drive shaft is essential to ensure safe and efficient operation.
During forklift operation, the drive shaft is subjected to significant torque and impact loads while rotating at high speeds. Continuous vibration and inadequate lubrication can cause wear, deformation, or damage, resulting in malfunctions, abnormal noises, and vibrations. For example, if the forklift trembles upon starting with a "clunking" sound, or if a periodic noise is heard while driving that increases with speed, this may indicate problems. In severe cases, the cab might vibrate, causing numbness in the hands while holding the steering wheel.
Common causes of these issues include loose or damaged cross shafts and needle bearings, loose fasteners, or a bent drive shaft. When such faults occur, it's important to inspect the vehicle’s bottom for loose bolts, manually shake the drive shaft to detect worn parts, and check the rear wheel frame and gears for movement. A dial gauge can also help identify any deformation in the drive shaft. Once the cause is identified, appropriate repairs should be carried out promptly.
If the dynamic balance of the drive shaft assembly is disrupted, additional dynamic loads due to centrifugal force can cause bending, leading to increased vibration, noise, and reduced efficiency. This can accelerate component wear and shorten the lifespan of the system. Accidental impacts, improper handling during disassembly, or misalignment after repairs can all affect the balance of the drive shaft.
When maintaining the drive shaft, it's crucial to apply grease to the cross bearing. To check for looseness, place the transmission in neutral, release the parking brake, and hold the drive shaft tube with both hands. A sharp left-to-right turn should not result in excessive play. If needed, the unit should be disassembled and repaired. During routine maintenance, ensure all fasteners are securely tightened, and inspect the drive shaft for damage or bending.
Before any repair work, all parts must be thoroughly cleaned, especially the cross shaft’s oil passages, journals, and needle bearings. Use clean kerosene for cleaning and blow dry with compressed air. Apply grease to mating surfaces and replace any worn components. After reassembly, the universal joint should move smoothly without noticeable play or sticking.
In the case of the CPCD50 forklift, the drive shaft connects the gearbox to the drive axle. It consists of a flange fork, universal joint, cross shaft, and bearing. A lubricating cup is provided on the cross shaft to allow for easy lubrication of the bearings. If excessive clearance occurs in the needle bearing, the drive shaft should be disassembled, and the cross shaft or needle bearing replaced based on the wear condition (always replace in pairs). Lithium-based grease is recommended for bearing lubrication. Never use thick greases like calcium-based ones, as they can increase wear and damage the bearings or cross shaft.
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