Nearly nine out of ten transmission failures are due to overheating and fluid contamination according to the Automatic Transmission Rebuilders Association.  Just like the oil in your car engine, automatic transmission fluid (ATF) suffers from heat, friction and electrochemical degradation. Once this process starts, your transmission’s vital parts begin to clog with sludge and form varnish deposits.

Unlike your car’s engine where all the oil can be drained out, most of the transmission fluid doesn’t drain into the transmission pan. Instead it stays in the torque converter, valve body and transmission cooler lines making a complete fluid drain impossible. In fact, the typical transmission service only replaces 25% of the contaminated fluid, leaving behind 75% contaminated fluid to mix with the new ATF.

According to automatic transmission fluid manufacturers, the addition of new fluid to contaminated fluid can actually cause sludge and varnish deposits to clog filters and restrict the flow of transmission fluid. This can result in a serious malfunction or even complete failure of an automatic transmission.

You should consider performing this service first if your car’s transmission fluid is showing signs of contamination or you are experiencing slippage, rough or hard shifting. This service is the first step before it becomes necessary to perform major repair work or install a replacement transmission.