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How To Repair When Abnormal Sound Of Gear-box?

Phenomenon of Malfunction

The abnormal noise of gear-box means that there is abnormal noise in gear-box which is mainly caused by the looseness of worn bearings and unusual engaged gears. The abnormal noise roughly takes place when tractor is in neutral or put into a certain gear. If there is always abnormal noise in different gears, the bearings are usually damaged; if there is continuous and high-pitched noise in a certain gear, it is caused by the gears; if tractor is put in a certain gear and there is continuous and depressing impact noise, it is caused by broken tooth; if there is no noise when pressing clutch pedal or have noise when loosing clutch pedal during parking, it is caused by normally engaged gears. Relevant parts should be focused on and repaired according to noise characteristics.

Judgment of Malfunction

1、 There is less fuel in gear-box, fuel quality is bad, the specifications of gear oil do not meet the requirements or there are impurities in it;
2、Bearings are worn to loose or damaged;
3、 There is gear eccentric wear or deformation of tooth caused by the inaccuracy of gear or improper process of heat treatment, the meshing clearance of gears is too small, gears are over-worn or the meshing clearance is too large;
4、The metal on the tooth surface of gear peels, the tooth of gear is broken or gear is assembled wrongly;
5、Spline hole and spline groove are worn severely and their match is loose;
6、Input shaft or output shaft is distorted;
7、The locking block of synchronizer falls off or synchronizer hub is worn and out of round;
8、 The lower end surface of gear shift lever and the groove of fork guide block are worn and cause looseness. The groove of self-locking device or steel ball is worn excessively, or self-locking spring is fatigue and broken;
9、The first or second shaft of gear-box or shifting fork is bended. The shifting fork is deformed or its fixing pin is loose.
10、 The gear box is not properly installed and positioned, and its fitting or connecting part of the operating mechanism is loose.


1、 If tractor drives at any speed in any gear, there is always the sound of metallic material’s dry friction in gear-box and a hot feeling is felt on the gear-box case, the oil level height of gear oil and its color should be checked. If oil level is too low or its quality is deteriorating, it should be refilled or replaced according to the requirements.
2、When engine runs on idle, if there is noise when gear-box is in neutral but the noise disappears after pressing clutch pedal, the gear box should be removed, and the rear bearing of the first shaft and normally engaged gears should be checked. Over-worn or damaged components should be repaired or replaced;
3、On the moment of pressing clutch pedal during starting or changing gear, there is strong sound of metallic material’s friction but the sound disappears when the clutch completely joints, the front bearing of gear-box’s first shaft should be checked to find out if it is worn loosely or damaged. If so, it shall be replaced immediately;
4、If there is no abnormal noise during the travel in neutral gear but the noise occurs during the start-up in any gear or during the shifting or travelling in any gear, the engagement of wheel gear or spline should be checked to confirm whether there is any abrasion, loose or damage, and whether there is any too small gap of engagement. The repair or replacement should be conducted if necessary;
5、If the gear box has any abnormal noise during its travel in neutral gear, but the noise weakens or disappears during its travel in high-speed gear, and the abnormal noise of “swoosh” occurs during the sliding in neutral gear, the loose degree of the second axle bearing of the gear box shall be checked. In case of any too serious loose or damage, it should be replaced;
6、If there is no abnormal noise during the travel in direct gear and the noise occurs in any other gears, the front and rear axle bearings on the direct gear thereof should be checked. In case of any abrasion, loose or damage, the replacement should be conducted;
7、Whether the gear box has noise during its travel in any gears, and the noise sounds louder during the speeding up, the gear box shall be disassembled. The housing, axle, wheel gear, spline and bearing thereof should be checked to see whether there is any serious abrasion or deformation. The repair or replacement should be conducted if necessary.

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