It's Not 1965 Anymore

It's been my experience recently that most vehicle owners are not aware of the much needed transmission fluid "flush and fill" service. Some of my customers are relating to the old school days of "dropping the pan" and replacing the filter, adding 4-5 quarts of new fluid, and calling that a transmission service. Actually, I think it should be called a disservice… and I will explain why, but first let me quote the Quaker State Technical Service Bulletin T-2002 A entitled Failure of an Automatic Transmission Immediately After Servicing, "Failure of an automobile transmission immediately after a change of fluid is not caused by the newly installed Automatic Transmission Fluid. Even a poor quality Automatic Transmission Fluid would not cause failure in just a few thousand miles.

The real problem is oxidation of the previous fluid, due to severe operating conditions, and/or over-extended use.

Since a large portion of the fluid cannot be drained, it remains in the transmission. Oxidation products, while soluble in the old fluid are insoluble in fresh new fluid, and thus precipitate out as sludge or varnish. These precipitated sludges and varnish then plug oil passages and screens, cause control valves to stick. This can result in serious malfunction, or even complete failure of an automatic transmission.

Carefully observing the Manufacturer's recommended drain interval is the best way to prevent this." This is found in your owner's manual under the 30, 60, 90K mile service. Towing will require that you flush and fill more frequently. Any of these operating conditions are especially severe in hot weather.

So now I will explain why "dropping the pan" is so outdated. Cars of yesteryear (50's and 60's) had a little feature not found on today's high tech automobiles…ok…are you ready? A drain plug on the torque converter. I know, you were waiting for something more profound. When this little drain plug was put into the six o'clock position, voila! Most of the old contaminated transmission fluid could be drained. Removing 4 quarts from the torque converter and 4-5 quarts from the transmission itself yielded 8-9 quarts removed from a transmission that held 10-12 quarts.

Proper flushing involves connecting a transmission flush machine in series (inline) to the vehicles transmission cooler lines which is usually somewhere at the radiator where the transmission fluid circulates giving up it's heat via the cooling system and then returns to the transmission. Vehicles set up for towing have an additional transmission cooler mounted in front of the A/C condenser.

Studies have found that most internal transmission filters are still 80% usable after 100K miles.

Next time a shop recommends to you that your transmission fluid is oxidized you can now ask, "Will I be able to have my transmission flushed and filled with approximately 16 quarts of the recommended fluid or will it be a "drop the pan," man, job?" Moving forward...

Jack Bergan, who has 38 years of experience in the automobile industry, is an ASE Master Technician and a member of the Automobile Service Association (ASA). Send comments or questions to drjack1@mindspring.com Questions will be answered in future columns.

Intensive Care Auto Repair, Inc.