In this article the common faults of the gear box will be discusses and suitable remedies suggested.
Noisy operation of the gear box
There may be two different cases i.e., the noisy running when the vehicle is stationary or when it is running in various gears.
This noise may be due to any or more of the following reasons:
- The bearings may be worn out in which case they will have to replaced.
- Countershaft may be worn, bent or having large end play. This has to be replaced with a new countershaft.
- Constant mesh gears may be worn out. The only alternative is their replacement.
- Shortage or incorrect grade of lubricant. The gear box should be filled with specified lubricant.
2. When vehicle is moving.
The possible causes of troubles in this situation are listed below:
- Gears may be worn out; they have to be replaced.
- Gears may be loose on the main shaft. This may be due to worn out splines or the gears on the main shaft. The worn out part should be replaced to remedy the defect.
- The bearings may be worn out in which case they should be replaced.
- The lubricant may not be sufficient or of wrong specification. If this is the reason of noisy running, the gear box should be lubricated immediately with proper grade of lubricant, otherwise running without lubrication will cause wear of many parts of gear box.
- Mounting bolts may be loose which may be tightened.
Hard gear shifting
The following may be the possible causes:
- Clutch adjustment may not be correct, which should be corrected.
- Clutch linkage may be binding. The same may be repaired or lubricated as required.
- There may be misalignment of the clutch housing. The runout at rear of clutch housing may be checked and corrected if necessary.
- The main shaft gears may be tight on splines. To remove the trouble the main shaft splines are cleaned and lubricated. If this is not effective, either the tight gear or the shaft has to be replaced.
- The gear shift mechanism may not be adjusted or lubricated properly, which must be done immediately.
- Synchromesh unit may be jammed or damaged. The damaged parts should be replaced. If no damage is there, then lubricate the unit immediately.
- Gear lever ball joint may be binding, which should.
Gears clash while shifting
If the gears clash while shifting from one gear to another, the probable causes are:
- Adjustment of clutch may be incorrect, which may be checked and corrected if necessary.
- Clutch linkage may be binding, which may be repaired or lubricated as required.
- Misalignment of the clutch housing may be another reason, which may be checked at the rear face and corrected if required.
- Components of gear shift mechanism or synchronizer assemblies may be worn or damaged. To correct this, the gear has to be removed and disassembled. On inspection, defective components may be identified and replaced.
- The lubricant may be of wrong specification or its level may below. To remedy, drain and refill the gear box with proper oil. Also, check for any source of leakage if the level was low and repair as necessary.
Gear locked in one gear
If the gear is locked in one position and cannot be shifted out of that gear, the causes probably are:
- Selector fork may be bent or selector rod(s) may be worn or broken, centre detent plug may be plug may loose or even missing. To correct, inspect the various components of the gear shift mechanism and replace the defective parts.
- Teeth on any gear may be broken. After inspection, the defective gear has to be replaced.
- Any other parts of the gear train may be worn or broken. To remedy, gear box has to be disassembled and defective parts replaced.
It may be experienced sometimes that the gear once engaged jumps out of engagement. The possible causes of this trouble are:
- The selector mechanism may be worn out or the springs may be weak. The replacement is the only remedy in this case.
- Gear on the main shaft ma very loose in which case it has to be replaced.
- The gear teeth or the dog clutch members may be worn out, which should be replaced.
- The worn out bearings may also be a source of this trouble by causing excessive end play of gear box shafts. The defective bearing must be replaced.
- The main shaft splines may be worn out or damaged. The main shaft has to be replaced in this case.
- Clutch shaft or roller bearings worn or damaged. The defective component may be identified by inspection and replaced.
- There may be misalignment of the clutch housing, which may be checked at rear face of clutch housing and corrected if necessary.
Leakage of the gear box oil
The possible reasons for this may be
- Damaged oil seals, which should be replaced.
- Damaged or even missing gaskets. The only alternative is the replacement.
- The bolts on the gear box cover may be loose, which should be tightened properly.
- The oil used may be thinner than the one specified. In this case the entire oil has to be drained and replaced with a fresh oil of suitable specifications.
- The breather hole (vent) at the top of the gear box may be blocked, which may be opened up.
- The oil level in the gear box may be higher than the required; the excess oil has to be drained out.
- The drain plug may be loose or damaged, which may be tightened or replaced as required.
- The gear box case may be cracked. If the cracks do not extend to the bearing seats, the same may be welded, otherwise it has to be replaced.