How to Repair an Automatic Transmission That Has Taken in Water
3 Answers
Avoid driving and running the engine as much as possible. Open the drain screw at the bottom of the transmission to drain all water and oil, then add new gear oil. If sand or silt has entered the bearings, especially the input shaft bearing, you will need to disassemble all components inside the transmission for cleaning. Fewer parts may need replacement, but components such as seals, gaskets, friction plates, as well as transmission fluid and differential oil must be completely replaced.
A few days ago, my friend's car encountered the same issue. Based on my experience helping him, if water gets into the transmission, you absolutely must not continue driving. The first step is to stop the car, turn off the engine, and call a tow truck to take it to a professional repair shop. The mechanic will remove the transmission oil pan to check the condition of the oil—if it appears milky or cloudy, it definitely has water contamination. Next, the transmission must be completely disassembled. All components need to be treated with specialized cleaning agents to remove water and rust, especially precision valve bodies. If the clutch plates or bearings rust, they are usually beyond repair and must be replaced, along with all seals. Finally, after reassembly, fresh oil is added, and gear shifting is tested. The entire process takes at least three to five days. This expense cannot be skipped—otherwise, if the transmission wears out due to water damage, a full replacement will be needed, costing twice as much.
My older automatic transmission had the same issue after driving through floodwater during a heavy rainstorm. Right after exiting the water, I immediately noticed jerky gear shifts, and by the next day, there was severe abnormal noise from the transmission. I rushed to an auto repair shop where they found the drained fluid was entirely emulsified—a mix of oil and water. The repair required a complete disassembly and thorough cleaning of the transmission internals, including removing accumulated water corrosion from the oil pan. Ultimately, the clutch plates and seals were replaced, costing around a thousand bucks. The key takeaway is to address it promptly before parts rust and seize. Also, after driving through water, it's wise to check the breather valve position, especially in vehicles where it's positioned low, as they're more prone to water ingress.
