The total transmission flush involves hooking up a special unit to the cooler lines of a transmission and doing a complete exchange of fluid. The good news is that you can replace virtually all of the old fluid with new. The bad news is that occasionally there will be some material that is disturbed and contaminates the valve body. Also, the filter is not changed because the pan is not removed, nor are you able to “read” any wear material residue that has accumulated in the bottom of the pan.
Personally, I’m not a fan of the flush. I still believe that a conventional transmission service is the way to go. Drop the pan, change the filter, replace the pan, and fill with fluid. Done properly, you should not have a leaking pan gasket.
The only time I would consider the flush is when someone is converting from conventional transmission to synthetic which is good for transmissions that are used under severe conditions such as commercial use, heavy loads, or towing.
There’s another method for changing the fluid called “suck and fill.” With this method, the fluid is sucked out the filler tube then new fluid is used to refill the transmission. The major problems with this technique is that the filter is not changed and there is no way to see any material collected in the pan. However, if you are changing the fluid frequently (at 10,000 to 15,000 mile intervals), you could use this method every other time.
