A red or brown stain under your car usually means one thing—transmission fluid is leaking. While a few drops may not seem like a big deal, ignoring a transmission leak can lead to much more serious problems. Transmission fluid doesn’t just lubricate—it cools the transmission and maintains the pressure needed to shift gears smoothly. Without enough of it, performance suffers, and internal damage can happen fast.
If you’ve noticed signs of a transmission fluid leak, here’s a look at the most common causes and what can be done to fix them.
1. Worn Transmission Pan Gasket
One of the most frequent sources of a transmission fluid leak is the gasket that seals the transmission pan. Over time, this rubber gasket can dry out, crack, or become damaged from heat and pressure. Leaks from the pan area are often easy to spot—a drip or small puddle right under the center or front of the car.
Replacing the gasket usually solves the issue, but it’s important to also check the pan bolts. Over-tightening them can actually warp the pan and make the leak worse.
2. Damaged Transmission Pan
The transmission pan itself can also be the culprit. Because it sits low under the vehicle, it’s vulnerable to road debris, curbs, or speed bumps. A dented or corroded pan can develop small holes or fail to seal properly against the gasket.
If the pan is damaged, replacement is usually the best option. When installing a new one, it’s smart to also change the gasket and inspect the fluid for signs of metal particles or discoloration.
3. Leaky Seals or Input/Output Shaft Seals
Your transmission has several seals that keep fluid inside while allowing components to rotate and function properly. Two of the most common to leak are the input shaft seal and output shaft seal.
The input shaft seal is located at the point where the engine and transmission connect. A leak here may show up between the engine and transmission housing. The output shaft seal, found at the rear of the transmission, can leak where the driveshaft connects.
Replacing these seals requires removing surrounding components but is essential to stop further fluid loss and protect internal parts.
4. Transmission Cooler Line Leaks
Automatic transmissions often have external cooler lines that carry transmission fluid to the radiator or a dedicated cooler. These lines can be made of rubber or metal, and both types are vulnerable to wear over time.
Rubber lines can crack or become brittle, while metal lines may rust or corrode—especially in areas with harsh weather. Replacing damaged lines or fittings is usually straightforward, but it’s important to use the correct type of line and clamp to ensure a secure, leak-free connection.
5. Torque Converter Leaks
While less common, the torque converter itself can develop leaks around the seams or where it connects to the transmission. Because this component is inside the bell housing, diagnosing and repairing the leak typically involves removing the transmission.
If you’ve ruled out other sources and the leak is still present, a faulty torque converter seal may be to blame. This kind of repair is more involved but necessary to avoid further transmission damage.
6. Overfilled or Overheated Transmission
Sometimes leaks aren’t caused by wear but by too much fluid or excessive heat. Overfilling the transmission can cause fluid to foam and overflow from the vent or seals. An overheating transmission can do the same, as expanding fluid forces its way out of the weakest point.
If you’ve recently had fluid added or changed, it’s a good idea to check the level with the engine warm and running—just like your vehicle’s manual recommends. If overheating is a concern, your shop can test the cooling system and transmission temperatures during operation.
Village Transmission & Auto Clinic – Trusted Transmission Leak Repair in Edmonds, WA
At Village Transmission & Auto Clinic in Edmonds, WA, we know how important transmission fluid is to the health of your vehicle. If you’ve noticed spots under your car, delayed shifting, or slipping gears, it might be a leak worth checking. Our technicians will find the source and fix it fast—before it leads to bigger issues. Stop in today for expert service you can count on.