Transmission leaks don't always happen for the same reason -- the repair might be as simple as tightening pan bolts, or as complicated as replacing the output seal.
Common Causes of Transmission Leaks
Transmissions often leak from a loose pan, caused when bolts aren't properly tightened after a filter is changed. Alternatively, drain plugs will leak when they aren't adequately secured after changing or flushing the transmission fluid. Although both leaks have an easy fix, they can cause major damage if they aren't addressed.
A frayed or cracked transmission pan gasket can also leak. This is a relatively simple repair, and the gasket itself usually costs less than $20.
Though less common, your car's torque convertor may be the source of a leak. The torque converter is a hydraulic pump that creates pressure in the transmission and sends fluid throughout the system. Sometimes, faulty needle bearings or cracks in the torque converter's body can cause leaks that are difficult to diagnose and expensive to repair.
Other Factors Contributing to Transmission Leaks
Transmissions are vulnerable to loose rocks on poorly paved road. If the bell housing is struck and damaged, for example, your car might be incapacitated by an immediate and significant loss of transmission fluid. A transmission's fluid lines can also be damaged by debris in the road. These are usually very durable -- made out of steel or aluminum -- but cracks or punctures will result in a leak.
Alternately, the mating surface of the transmission's pan gasket could be warped. This would prevent the gasket from sealing properly, allowing fluid to escape. When replacing any gaskets, always check all surfaces for warping or other damage to the surfaces that can keep the gasket from sealing.
The Environmental Consequences of Transmission Leaks
Transmission leaks cause problems for your vehicle, obviously, but they're also a significant concern for our environment. In fact, fluid leaking from faulty transmissions is as toxic as other petroleum-based products like gasoline or motor oil. Left unattended, transmission leaks can cause serious damage to an ecosystem.
Good for Your Car but Not the Environment
When pollutants from a transmission leak filter into the soil, they disrupt checks and balances in the ecosystem. Contaminated soil may lead to the poisoning of insects and rodents needed to control pests that can damage crops or spread disease.
Transmission Fluid Is a Danger to Our Water Supply
Leaked transmission fluid can find its way into our water system. Even if a transmission leaks fluid onto asphalt or concrete, it can find its way into water that is consumed by animals and humans. Rains can carry toxic chemicals into reservoirs or waterholes. In short, transmission fluid leaks will almost always find their way into a water source.
How to Protect our Environment
Check underneath your vehicle for any signs of transmission fluid leakage. It will usually appear to be bright or dark red, and is easily seen once a vehicle is moved. If your transmission is leaking, be sure to have it repaired as soon as possible.