1. Causes of "Gear Skipping"
(1) Wear of the Transmission Mechanism: The W4-60 excavator uses a mechanical gear shifting transmission mechanism. This mechanism relies on a sliding gear sleeve moving axially on a fixed gear sleeve and meshing with the driven gears of each gear to achieve gear shifting. During frequent gear shifting, the end faces of the teeth of the meshing gears are easily worn into a conical shape, resulting in reduced meshing performance and causing "gear skipping."
(2) Deterioration of the Self-Locking Mechanism: To prevent gear skipping, this type of excavator has steel balls and springs installed in the cover holes above the II, III, IV, and V gear shift fork shafts and in the I and reverse gear shift forks for self-locking. When the elasticity of the springs acting as positioning and self-locking weakens or breaks, the self-locking performance of the self-locking mechanism will decrease or even disappear, causing the transmission to "skip." Wear on the positioning steel balls or the grooves on the shift fork shafts can also cause gear skipping.
(3) Improper adjustment of the gear shifting device: This type of excavator uses a mechanical manual gear shifting method. Loosening of the gear lever, longitudinal shaft, transverse shaft, and vertical fixing screws can also cause the gear shift to "jump gears".
(4) Sudden changes in external load: Due to the nature of the excavator's work and its design, sudden changes in external load can also cause the gear shift to "jump gears". When the road surface is uneven, the machine is traveling downhill, or the travel route is improper, causing a sudden change in external load, this sudden change in load will act on the gear engagement gears of the gear shift through the wheels and drive shaft, causing the gear engagement gears to disengage due to axial thrust, resulting in the gear shift to "jump gears".
(5) Improper operation: When the excavator is traveling on a slope (especially downhill), improper operation can also cause the gear shift to "jump gears".
2. Preventive measures
(1) Strictly follow the operating procedures and driving techniques to avoid "gear grinding" during gear shifting, thereby reducing wear on the gear pairs.
(2) Strictly implement the maintenance system and strengthen the maintenance of the gear shifting device. When the shift mechanism linkage is improperly connected, it should be adjusted promptly to ensure the shift mechanism performs well.
(3) Pay attention to the maintenance and upkeep of the self-locking mechanism. Positioning steel balls, springs, and shift fork shafts that have reduced or lost their positioning effectiveness should be repaired or replaced promptly to ensure the self-locking performance of the self-locking mechanism is in good condition.
(4) When assembling the transmission, strictly follow the operating procedures to ensure that all transmission components are correctly adjusted and properly tightened. On steep downhill slopes, the driver must strictly follow the downhill operating procedures and must not violate any regulations.
3. Emergency Handling Methods
If the transmission "jumps gear" during the excavator's operation, the machine should be stopped immediately (or the machine can continue driving), and then the cause should be identified and the fault eliminated. Specific methods are:
(1) If "jumping gear" occurs while driving on a flat road, stop the machine according to the normal stopping procedures, carefully identify the cause, and eliminate the fault.
(2) If "gear skipping" occurs while driving uphill, shift to a low-speed position or I gear. Stop the machine when it reaches the top of the slope to troubleshoot the problem. If downshifting fails or "gear skipping" occurs again, stop the machine according to the procedures and requirements for stopping on a slope, and then troubleshoot the problem.
(3) If "gear skipping" occurs while driving downhill, shift to a high-speed position according to the procedures for upshifting or take "emergency downshifting" measures. Stop the machine when it reaches the bottom of the slope to check and troubleshoot the problem. If upshifting or "emergency downshifting" fails or "gear skipping" occurs again (in neutral), the driver can control the engine speed at medium speed (to prevent the engine from stalling) and use "intermittent braking" to allow the machine to slide to the bottom of the slope, and then troubleshoot the problem. If "upshifting" or "shifting up" fails, or if the machine jumps out of gear again (into neutral), and is on a steep downhill slope (where it will rapidly plunge towards the bottom), immediately follow the downhill stopping procedure and requirements, then troubleshoot the problem.
1. Check if the pilot pressure for the slewing operation is within the normal range (normal pilot pressure is above 35KG);
2. Check if the slewing relief valve is damaged, and if the slewing relief pressure is within the normal range (relief pressure: 280KG);
3. Check if the slewing main valve core is switched to the correct position, and if the slewing valve core return spring is broken;
4. Check if the distribution valve is worn or damaged, causing internal leakage in the slewing motor;
5. Check if the slewing motor pump body and plunger are worn or damaged, causing internal leakage in the motor;
6. If only the slewing operation is slow while other operations are normal, then the main hydraulic pump and main relief valve can be ruled out as faulty.
