Common gearbox problems and their solutions

A gearbox is an important component of the vehicle that transfers power from the engine to the wheels.

The gearbox is also known as the transmission.

It is made up of a series of gears that transmit torque from one rotating shaft to another at different ratios, allowing the engine to operate efficiently over a wide range of speeds.

There are two gearbox variants: manual and automatic. The two variants have different numbers of gears to suit varying needs.

In the manual gearbox, the driver is fully in charge of shifting the speeds that he or she wants.

The selection of a gear number is done to suit the current driving conditions and needs.

The automatic gearbox allows the vehicle to respond to the driver's command on acceleration and deceleration.

When the driver presses more firmly on the acceleration pedal, the higher the number of the gear, and the faster the vehicle moves.

Without a functioning gearbox, the vehicle is useless.

Many motorists in Kenya, and other parts of the world, have often filed complaints about gearbox problems, especially among certain models of vehicles.

Some gearbox glitches can be repaired, while others require complete overhaul of the system.

Regardless the kind of action needed, gearbox repairs are generally expensive.

Cash for Cars estimates that repair costs could be anywhere between $300 (Sh38,000) and $1,500 (Sh190,000). Buying a new gearbox, as per the platform, would set you back between $1,800 (Sh230,000) and $3,400 (Sh430,000).

The cost of repairing a gearbox varies, depending on several factors, including the type of vehicle, the complexity of the transmission system, the severity of the damage and the cost of spare parts and labour.

The labour cost could rise exponentially if the transmission system is difficult to access or requires specialised tools or expertise. Rebuilding a gearbox is time-consuming too. The overhaul of a vehicle's gearbox can take up to a week for some cars, while most take between one day or two.

So, what are the most common gearbox problems that motorists experience?

Gear slipping

This occurs when the gearbox slips out of gear and back into neutral or engages the wrong gear. This glitch is mostly caused by low transmission fluid, damaged clutch or worn out synchronisers that are responsible for transmitting angular data electrically from one location to another.

One of the easiest ways to fix and prevent gear slipping is to monitor the transmission fluid level. Once a month, check the fluid level when the engine is running. If low, top it up with the recommended transmission fluid.

It's inexpensive to fix gear slipping, because what is needed is transmission fluid top-up or change. Transmission fluid costs vary, depending on the type, make of car and place of purchase. The prices start from Sh4,500.

Noisy transmission

It is a common issue, especially among old vehicles that are not serviced periodically.

Charles Okoth, a mechanic based in Nairobi, says most drivers, especially those operating PSVs, tend to ignore the noise from the engine, assuming it is as a result of normal combustion.

"In most cases, the noisy transmission is caused by worn out gears, bearings, or input and output shafts. It can be a sign of a serious problem, and should be addressed urgently," said Okoth.

The noises can be in the form of grinding, whining, clunking and gurgling.

Transmission fluid leaks

This is the commonest cause of gearbox breakdown. It mainly occurs due to worn out seals, gaskets, or damaged casing.

It is advisable to regularly check beneath your vehicle for any leaks.

In case of a transmission fluid leak, you'll need to purchase a new gasket, which is affordable, and make sure the bolts in the pan are tightened. If they are not, this could result in a leak. Most times, the pan isn't secured properly after a transmission fluid change, causing a transmission leak to occur.

Gear grinding

This is often caused by a mismatch between the speed of the clutch plate and the transmission.

Mechanics warn that constant use of cheap transmission fluids can also result in gear grinding. It can damage the transmission if it persists, and this could lead to the need for a complete overhaul of the gearbox.

Difficulty shifting

This is usually caused by a damaged clutch, worn out synchronisers, or linkage problems. It is common with manual vehicles. Continuous use of a vehicle with difficulty in shifting, can completely damage the gears, which might necessitate a gearbox overhaul.

Clutch problems

A clutch is a mechanical device that is used in a vehicle to engage and disengage the power transmission between the engine and the gearbox.

When the driver removes his or her foot off the clutch pedal, the clutch disc is released from the engine's flywheel, which separates the engine from the gearbox.

This allows the driver to change gears or bring the car to a stop without stalling the engine.

A worn-out clutch can cause difficulty shifting gears, and may result in a slipping clutch.

"Common symptoms of clutch issues include a burning smell, difficulty engaging or disengaging the clutch or a clutch pedal that feels spongy or unresponsive," said Nairobi-based mechanic Charles Okoth.

"In automatic vehicles, there is no clutch pedal as the transmission uses a torque converter instead," he added.

Overheating

This can be caused by low transmission fluid levels, excessive use of the vehicle, or a problem with the cooling system. Overheating can cause extensive damage to the gearbox.

"It is important to always observe the Automatic Transmission Fluid (ATF) levels. The gears need to be lubricated at all times. However, remember not to overfill the ATF reservoir since this can cause overflows due to bubbles trying to escape from the tank and broken seals," said Okoth.

CVT

Automatic vehicles also operate on CVT transmission, which has gained notoriety for developing a number of issues.

CVT stands for continuously variable transmission.

A CVT is similar to an automatic in that it doesn't use any input from the driver, but that is where the similarities end.

A CVT doesn't have any gears. Instead, it has two pulleys. One pulley connects to the engine, and the other connects to the wheels. A flexible belt connects the two pulleys.

Car And Driver, a car review platform, says a CVT can provide a smoother driving experience when comparing it to a traditional automatic.

One of the major advantages of the CVT, is that it is more fuel-efficient compared to a regular automatic.

Some of the common problems that CVT vehicle owners run into include overheating, slipping, sudden loss of acceleration and shuddering.

Since CVTs depend on the belts to operate, if these suffer from excessive stretching or too much wear, the transmission can completely fail.

Other issues with the CVTs include their inability to last as long conventional transmissions, and the CVTs being harder to work on. Even basic maintenance often needs to be done by trained personnel.