Signs of a Faulty Car Gearbox: What to Look Out for & How to Maintain It

A car’s gearbox is a vital component as it ensures that your car drives smoothly at any speed. It controls the torque and speed of your car so you have the right amount of power when you need it and that it’s delivered smoothly. 

Driving with a faulty gearbox will not only give you a rough and jerky ride, but could cause your car to stall in the middle of the road. That’s why it’s important to maintain your gearbox. So, here’s how to identify the symptoms of a faulty gearbox.

manual gearbox - shifting gear

What Is a Car Gearbox?

When combustion happens in your engine, the power is transferred to the crankshaft which rotates thousands of times per minute. However, this is too fast for the wheels, so the gearbox converts the power to a rotational speed that the wheels can manage. A conventional gearbox has numerous gears with interlocking teeth which connect to the output shaft.

When driving at lower speeds or uphill, lower gears are used. Low gears have larger cogs which allow the engine to deliver more torque to the wheels. At higher speeds, higher gears are used instead. High gears have smaller cogs which deliver more speed and lower torque, allowing for smooth driving and better fuel economy on the highway.

Read More: Auto Versus Manual Transmission

7 Signs of a Faulty Car Gearbox

A gearbox can generally last for more than 150,000 kilometers or for throughout the car’s lifetime with proper maintenance. However, there are times when your gearbox can malfunction, such as with poor driving habits and maintenance. By knowing what to look out for in your car, you can identify issues with your gearbox early and avoid needing major repairs.

1. Burnt Smell from the Engine Bay

If you notice a smell like burnt rubber or smoke coming out of your engine, it could indicate some issues with your transmission as burnt transmission fluid has a uniquely harsh smell, similar to burning rubber. If this is accompanied by fluid leakage, it’s a sign that your transmission fluid levels could be dangerously low which can lead to friction on the gears which can lead to the gearbox overheating and catching fire. 

In some cases, a burnt smell can also be caused by radiator issues or insufficient engine oil. If you notice any unusual smell from your engine, immediately get it checked at the workshop.

Read More: How to Check the 6 Essential Car Oils & Fluids

2. Unusual Sounds from the Gearbox

Another sign of a faulty gearbox is if you hear unusual sounds, especially when shifting gears. As there are hundreds of parts in the gearbox, even a single worn or loose bearing can produce unexpected noises. 

Oftentimes, a faulty automatic gearbox will produce humming, whining, or buzzing noises, while a manual gearbox tends to produce harsher clunking noises. Do note that these noises may also indicate problems with the engine, drive shaft, or exhaust, so you should get your vehicle checked to pinpoint the issue.

3. Lack of Response When Shifting Gears

A difficulty to shift gears is often a clear indication of a faulty gearbox. This can be caused by several reasons including a clogged transmission filter, incorrect transmission fluid, and faulty sensors or solenoids. In vehicles with an automatic gearbox, there may be a delay in the time the gear engages when you shift from drive to park. 

In a manual gearbox, unresponsive gear shifts can result in a disconnect between the engine’s revolutions per minute (RPM) and the actual vehicle speed and motion. This means that your engine could be revving high but your vehicle isn’t accelerating.

Read More: What Is a Car Engine Overhaul and When to Do It 

4. The Gear Gets Stuck When Shifting

If your gearbox won’t go into gear, this could be an indicator that you could have several issues. These include mechanical failure, a clogged filter, faulty clutch linkage, incorrect transmission fluid, a malfunctioning computer system or sensor, and other issues. This problem indicates serious issues, so you should get your gearbox repaired immediately as delaying it could result in you needing to replace your gearbox.

5. Gear Slipping

Gear slipping happens when the gear “slips” between gears such as from first into neutral without you shifting gears yourself. Gear slipping most commonly happens right after you shift gears, and usually slips into neutral. This is extremely dangerous as it could cause your car to suddenly stop moving or lurch forward, endangering yourself and the people around you. 

In a manual gearbox, gear slipping is often caused by a worn-out clutch, while in an automatic gearbox, slipping can be caused by wear and tear on various parts such as the clutch plates and transmission bands. Many modern gearboxes have a safety feature called “limp mode” or “safe mode”. This happens when the computer detects a problem with the gearbox and defaults to only one gear to prevent further slipping and allow you to safely drive to a nearby workshop.

6. The Transmission Warning Light Comes On

Having the transmission warning light come on is often a clear sign that there are issues with your gearbox. The warning light responds to sensors that can detect minor, unusual vibrations that you may not notice, and are located at crucial points in the gearbox. Therefore, you should never ignore it when the warning light comes on. Instead, get your car checked at the workshop immediately.

7. Gearbox or Transmission Fluid Leakage

The transmission fluid functions as a lubricant to decrease friction and as a hydraulic fluid to enable gear engagement in the gearbox. If you have a transmission fluid leakage, your gearbox won’t have enough lubrication. The increased friction can wear down the gears and eventually cause overheating in the gearbox. 

If you see a pool of bright red fluid beneath your car, it’s a sign of leaking transmission fluid. However, if the leaked fluid is dark brown or black and smells like burnt rubber, it could be burnt transmission fluid. In this case, there might already be significant damage requiring major repairs on your gearbox.

Read More: Things to Check When You Service Your Car

gearbox/transmission

4 Automatic Gearbox Maintenance Tips to Keep Your Gearbox in Shape

Repairing or replacing a gearbox can cost a bomb even for compact affordable cars. For example, the price of a genuine automatic gearbox for the Perodua Myvi starts from RM6,000 (including installation) but you can find reconditioned Myvi gearboxes from under RM1,000. By properly maintaining your automatic gearbox, you can extend its service life and reduce the risk of it breaking down – here are some ways. 

1. Regularly Check Your Transmission Fluid

Just like with your engine oil, you should periodically check the level and condition of your transmission fluid. If your transmission fluid level is low, it might mean that you are overdue for a gearbox service or that you have a leakage in your gearbox. Also, do note that transmission fluid that’s in good condition is clear, bright red, and has a slightly sweet smell. If you notice that the fluid has a dark color and acrid smell, it’s time to change it immediately.

2. Avoid Driving with a Space Saver Spare Tire for Too Long

In most cars, the spare tire is narrower than the regular tires to allow it to fit in the boot. Due to its size, it’s also called a space-saver tire. Driving with a space-saver tire might not seem like a big deal. However, you might unknowingly be damaging your gearbox if you drive your car for extended periods of time with it. The reason for this is that driving with mismatched tires puts a strain on your car’s gearbox and other drivetrain components. Driving with mismatched tires can also affect the alignment of the wheels as there will be an unequal force on the wheels and suspension system.

3. Use the Right Transmission Fluid

Each car gearbox needs the correct fluid, as specified by the manufacturer to run optimally. As different transmission fluids contain different additives and specifications, some fluids may not be compatible with your gearbox. Therefore, make sure to check your owner’s manual and take note of whether you need a manual transmission fluid, automatic transmission fluid, or CVT fluid for a continuously variable transmission (CVT).

4. Conduct Regular Maintenance on Your Gearbox

Regular maintenance will not only ensure that your gearbox functions smoothly but also increase its lifespan. As the gearbox service interval varies between car models, you can check your owner’s manual to find out the recommended service interval for your car. A gearbox or transmission service generally involves these steps:

  • Examining the gearbox and other components including the sump pump or pan.
  • Flushing and replacing the transmission fluid.
  • Replacing the transmission filter.
  • Cleaning the transmission pan and installing a new pan gasket.

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