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Gearbox Failure: 5 Most Common Reasons Explained

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The 5 Most Common Conditions that can Lead to Damage of Your Gearbox

Gearbox Failure The Most Common Reasons Explained

While the engine might be what provides the power, the gearbox is actually the heart of any vehicle. Without a functioning gearbox, the power produced by the engine cannot be transmitted to the wheels, meaning that you’re stuck in one place if it fails. And, make no mistake, gearbox failure can and does happen. Protecting your fleet vehicles from premature damage is important and will require that you understand the most common reasons that gearboxes fail.

Gearbox Fluid-Related Issues For Gearbox Failure

The single most common reason for gearbox failure is improper Gearbox fluid level. Unlike engines, gearboxes don’t “burn” fluid. Low Manual Transmission fluid levels are the result of leaks that have gone unnoticed and unrepaired, so this is directly related to poor maintenance. When Gearbox fluid levels drop too low, it robs the gearbox of the lubricant it needs to prevent wear and tear, as well as creating operational problems due to a lack of fluid pressure. The most common sites for fluid leaks include at the driveshaft, interior seals, and gearbox gasket seals.

Fluid Related Issues
Torque Converter

Torque Converter

The second most common reason for gearbox failure is a problem with the torque converter. This sits between the gearbox and the engine and allows the engine to spin independently while still pressurizing the fluid within the gearbox so that the gears will shift. Needle bearing wear and failure is the most common torque convert-related issue, but there are others.

Solenoid Issues For Gearbox Failure

Another very common gearbox-related problem is an issue with the solenoid. It is responsible for controlling the flow of fluid within the gearbox, so when it experiences problems, the gearbox will not shift properly, or not at all. Solenoid issues can be caused by low fluid levels, but also by solenoid failure. The good news is that this is usually a simple replacement to make.

Solenoid Issues
Clogged Gearbox Fluid Filter

Clogged Gearbox Fluid Filter

Every vehicle has a gearbox fluid filter, which is responsible for catching debris suspended in the fluid and preventing it from building up within the gears and other internals. The filter should be cleaned periodically during manufacturer-recommended gearbox maintenance services. If service is neglected, the filter can become clogged, which affects fluid pressure and flow throughout the system. This can cause damage to the gearbox and will affect operability, too.

Incorrect Or Low-Quality Gearbox Fluid

Each gearbox requires a specific Gearbox fluid type formulated to its needs. Using the wrong fluid in a drain and fill, or replacing old fluid with inferior quality fluid, will lead to gearbox damage and potentially to failure. Always ensure that you are using OEM-quality Gear and transmission oil. This does not mean that you must purchase gearbox fluid from the vehicle manufacturer, but you do need to ensure that the fluid you purchase meets or exceeds industry and manufacturer standards.

Low Quality Gearbox Fluid


Ultimately, the most common causes of gearbox failure have to do with improper maintenance and failure to catch leaks before they deplete fluid levels to critical levels. It is essential that you monitor the gearbox, driveshaft, and other seals for signs of leakage, while also checking fluid level and color periodically.

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