Common gearbox problems and their causes

Since transmission fluid has a characteristic petroleum smell and is red in colour, it is easier to detect. A leak is likely to create a pool under your car. PHOTO | COURTESY

What you need to know:

  • You car’s gearbox completes its function of transmitting power to the wheel from the engine through continual grinding, rotation and combating friction which causes several inevitable gearbox problems.

A gearbox is one of the units that completes the drive train and is the only part of the car that connects the tyres to the engine. Essentially, the gearbox lowers rotation speed from the input to the output shaft by a ratio of 30:1. The reverse is true for an increase in torque. Additionally, the gearbox must never be overloaded but fairly balanced to avoid bending fatigue or worse.

Wear and tear 

Gearboxes have moving parts; gears and clutches and all these create friction and a lot of heat, which in turn creates wear and tear and that is where you need a lubricant to handle the heat and reduce the friction or wear. However, Robin Byaruhanga of Deutsche Auto Services UG, says lubricants have a lifespan that determines its viscosity or strength as well as quality of the lubricant to handle the elements. 

“Just like engine oil, lubricants age with time and as per manufacturer’s instructions, they need changing after a certain period. However, most drivers do not pay attention to it yet these moving parts need lubrication to keep them running smoothly. Many only wait for the component to fail only to end up paying huge repair bills,” Byaruhanga says. He adds that for drivers who are not sure of when to change their lubricant, reading their user’s manual or consulting a mechanic is the way to go.

Hard shifting 

Difficulty shifting from one gear to the next can be caused by a number of things. Paddy Gumisiriza, a mechanic, says some of the reasons are improper clutch adjustment, remote control shifting mechanism out of adjustment, distorted splines of the main shaft, battered gear teeth or even extremely strong shifters lock spring. 

“All these call for early assessment to avoid breakdown of other components. For instance, when the teeth break, this means the gear lever may soon start failing, leading to inability to get the gear you want,” he says.

Oil leakage 

There are instances when oil starts leaking from the gearbox due to oil being above the maximum level, a loose drain or filler plug, loose cover bolts, damaged or poorly fitted oil seals or gaskets. While instances of oil being above maximum are rare, Gumisiriza says, there is a possibility of one poorly replacing the gearbox cover, thus a leakage. 

“Since the cover is under the gearbox, any mistake in tightening it may cause damage. A cracked case or cover also needs to be replaced quickly. That is not to say that the other issues do not need immediate attention,” he says.

Howling or whining sounds 

While lubrication shortage will cause the gearbox teeth to rub against each other hence making whining sounds, corrosion also does the same. 

“Even after oil replacement, the damage is done and is irreversible. That is why topping up oil promptly is crucial. Additionally, when water gets into the gearbox oil, it could damage the steel surface by causing indentations and unusual wear,” Byaruhanga says. 

While wear and tear is unavoidable when using a gadget, with the gearbox, frequent gear cleaning reduces it.

Rumbling sounds 

Gumisiriza says rumbling sounds as the car engine runs is a sign of a faulty ball bearing. If one has seen a bicycle chain, ball bearing are the small balls on the chain meant to ensure that there is right clearance between gears. In the gearbox, they are sensitive to metal bits and dirt that are sometimes found in the lubrication between the bearing elements. 

“Metal bits and dirt cause the bearing to drag on the race surface, hence wearing out. The more the foreign elements, the faster the wear and tear,” he says. When not fixed, the noise will get louder which also means that the wear and tear is increasing and could cause the gear teeth to misalign which also damages the gearbox. 

Grinding sounds 

Such sounds may happen at different times. For instance, it could be as the engine runs yet in neutral. In this case, it could be your car’s clutches slipping within the transmission or at times, because there is loss of transmission fluid. However, it might also be because the gearbox is not well aligned with the engine. 

“This causes the gearbox and the flywheel’s shaft to bind,” Gumisiriza says.

In another case, the grinding might be when you are shifting gears. It may occur after totally pressing the clutch pedal, which he says may be a sign of a worn out clutch pedal. However, if it happens when your foot is off the clutch pedal, then he says it may point to a problem with your gear synchronisers. 

“Even then, the components must be replaced promptly so the damage is not transferred to the gearbox,” Gumisiriza says

Lack of acceleration 

Sometimes, as you drive, your car might delay to accelerate. 

“While it may not cause alarm if infrequent,an increase in the revolutions per minute while the acceleration remains low may be due to a faulty clutch component such as worn out plates, master cylinder or presence of air in the fluid channel,” Byaruhanga says.


•Check your gearbox transmission fluid level regularly to ensure there is no insufficiency.

•Warm up your car to allow the fluid to flow through all the parts of your gearbox and prepare for a drive.

•Never overheat your vehicle transmission as it causes problems such as damaged or cracked gear, broken seal and faulty bearing, among others.

•Additionally, always be extra careful to switch gears properly to ensure the transmission is functioning right.

•Use your car’s parking brake to park your vehicle for preventing unwanted wear and tear.

•Not overloading your car may seem ignorable but is crucial for preventing damage to your gearbox.

• Take your car for regular servicing and an annual check-up of powertrain transmission.


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