NB & NCII V8 Fairlanes
Join Date: Feb 2001
Location: Bibra Lake Western Australia
Re: Flushing AU Falcon Transmission
Yes; I do it biannually on both my two Fairlanes. After draining the sump (fit a drain plug when you have the pan is off so it is easier the next year) and changing the filter and refilling the sump and adjusting the bands you need to get the rest out of the torque converter, lines, radiator and trans cooler. I used to use a Mityvac vacuum pump to suck it out from the inlet hose (you can't blow it out with a compressor as the oil will foam) on the trans cooler but it is easier and much quicker to let the transmission pump do it for you. After making sure the oil in the refilled sump is at the correct level for a cold transmission, remove the outlet pipe from the transmission cooler and run a tight fitting hose from transmission cooler outlet (top pipe) to a 5 litre container that has marked litres on the side (an old plastic transmission fluid container, plastic engine oil container or plastic coolant container works fine). Something with a relatively small opening so there is less chance of the hose coming out and trans oil going everywhere.
Now get a trusted assistant to start the motor while you watch the old transmission oil going into the container. Leave the transmission in park during the following procedure. Once a litre is in the container tell the assistant to stop the engine and top up the trans to the cold engine max level dip stick mark again. Keep doing this a litre at a time until the oil runs clean. I find I need 12 litres to 15 litres (including the initial 3.5 litre sump fill) of transmission oil to do this although a full refill is meant to be only 10 litres. Remember to check the trans level again after the engine is hot and the transmission has been cycled through PNDR123 a few times. Try to do this procedure on a hot day as the transmission cooler is self regulating with small tubes that cold oil will not run through. If you do it on a cold day it will take a minute or so before the oil flows and you will need more transmission oil as the clean oil in the sump will be diluted with old oil. Alternatively you can take it for a warm up run and know that you will have to replace the 3.5 litres of new oil you used to refill the sump and estimate by touch when you swap from using the hot mark to the cold mark on the dip stick.
Note this will not get metal contaminants out of the system if the transmission has failed. in such cases the radiator and trans cooler will need to replaced as they will be blocked by the metal fragments; similarly the transmission itself need to be stripped and thoroughly cleaned after any major component failure.