Gearbox Troubleshooting - Engineering Projects

In the article Gearbox Troubleshooting, the common faults of the gearbox will be discussed and suitable remedies suggested.

Noisy operation of the gearbox | Gearbox Troubleshooting

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 replace.
Countershaft may be worn, bent or have 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 gearbox should be filled with specified lubricant.

The possible causes of trouble 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 the wrong specification. If this is the reason for noisy running, the gearbox should be lubricated immediately with proper grade of lubricant, otherwise running without lubrication will cause wear of many parts of the gearbox.
Mounting bolts may be loose which may be tightened.

The following may be the possible causes:

Clutch adjustment may not be correct, which should be corrected.
The clutch linkage may be binding. The same may be repaired or lubricated as required.
There may be a misalignment of the clutch housing. The runout at the rear of the 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.
The 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.

If the gears clash while shifting from one gear to another, the probable causes are:

Adjustment of the clutch may be incorrect, which may be checked and corrected if necessary.
The 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 the wrong specification or its level may be below. To remedy, drain and refill the gearbox with proper oil. Also, check for any source of leakage if the level was low and repair as necessary.

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.
The 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 this, the gearbox 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 gearbox 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 a misalignment of the clutch housing, which may be checked at the rear face of clutch housing and corrected if necessary.

The possible reasons for this may be

Damaged oil seals, which should be replaced.
Damaged or even missing gaskets. The only alternative is replacement.
The bolts on the gearbox 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 fresh oil of suitable specifications.
The breather hole (vent) at the top of the gearbox may be blocked, which may be opened up.
The oil level in the gearbox may be higher than 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 gearbox 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.

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