What is the consensus on changing transmission fluid? I have a 93 LT1 base I bought 3 years ago. It had 16K miles on it when I bought it and it still had the original everything except the tires, air filter, brake fluid, and fuel filter which I changed. I'm just wondering if I really need to change the trans fluid. The transmission shifts perfectly so I am hesitant to do anything to it. What are your thoughts? It also has the original plugs and wires.

 

30 year old fluid? yes change it and the filter.

 

When I pulled my original 96 trans filter it seemed like somewhat different filter media compared to the new one. Not really hard to believe they have made advances in filter tech in the last quarter of a century. Dan

 

You can check the plugs easy enough and look for cracks in the ignition wire insulation. But I routinely change all fluids on any used car I buy and I don't rely on any verbal communication of what was last serviced and when it was done. Many of these sellers just lie to me about maintenance. Brake fluid, P/S fluid, Trans fluid, antifreeze, oil, differentials, chassis lube: all of it. I find it to be a satisfying Saturday's work. It's good you did the filters too, often overlooked by previous owners.

 

I did the brake fluid as soon as I got it. I believe in having good brakes. I've done the fuel filter and the air filter and of course, I change the oil and filter every year. I've never changed the trans fluid in any car I've ever owned. I usually buy a new one every 10 years and drive it 100k miles and then get a new one. I just wondered about the trans fluid, I've never owned a car this old before. If it works good I usually don't mess with it. But, it looks like the consensus is I should change it, so I probably will.

 

The word "change" gets thrown around incorrectly a LOT on forums and real life when it comes to transmissions. My FiL even said "changed" every 30k miles about his farm truck. Even tho all he actually did was drain the pan, and refill it. He also got mad that he had to replace that Allison every 120k.... On our 1 ton trucks an auto can hold 21 quarts of ATF in the system, so the 3 quarts in the pan is beyond a less than adequate fluid "change" . You wouldn't change your engine oil filter and pour in 1/2 quart and claim you "changed" oil would you?

I'll assume this is an auto we're talking about.

To "change" fluid vs just a pan refill requires more effort and cost. You'll need 3 more quarts than the entire system holds. The first step is dropping the pan and replacing the filter and resealing the pan. The next step is disconnecting the return line from the transmission cooler at the transmission. Then you refill the pan from the the dipstick tube and keep the funnel in the fill tube. Attach clear tubing to the return line and run this into a 5 gallon bucket you can see from the funnel's location. Then start the vehicle and continue to pour new fluid into the funnel watching the clear tube pump old fluid into the bucket. Once you have successfully flushed the entire system (transmission pan, torque converter, and coolers) the fluid will change color. Once what comes out of the return tube to bucket is the same color as brand spanking new ATF from the bottle shut the vehicle off. Then reattach the cooling line to the transmission, start the vehicle and check fluid level. Let the vehicle idle all the way up to full operating temp. (The radiator fan will kick on)

Then check fluid level with it running; to correctly top off an automatic transmission the vehicle must be running and at temp.

And that is how you "change" transmission fluid. Otherwise you are just mixing a little bit of new fluid with the old junk. Which is usually 4 to 9 times as much as the pan holds depending on the vehicle.

This is the same basic procedure for all autos. A friend of mine used to design and then test to failure point, transmissions @ Ford for 30 years and this is the procedure he recommends to anyone and everyone that will listen to his experience. Yeah, buying 24qts of full synthetic ATF sucks on large vehicles, but it's still way cheaper than a transmission rebuild

 

First thing I did after buying my 86, most fluids & filters.

 

I wondered about the fluid in the torque converter and how you would change it? I didn't know if you had to take the transmission apart or what! Why do you need to drop the pan? Wouldn't that fluid cycle out or is it mainly to change the filter? That doesn't sound too difficult to accomplish and you have all new fluid. Thanks for the explanation Flannel_man!

 

When you start the engine to run the fluid into the bucket do you put the transmission in Park, Neutral, or drive ?

 

Definitely park. Drive would be deadly, Neutral would rely on chocks or some other means to keep from rolling as well.

If it weren't pumping fluid while in park the transmission would seize in the parking lot or driveways long before driving in D or using N.

​​​​​ Remember, the fluid isn't just used to convert mechanical energy into hydraulic and back into mechanical, it's also used to lubricate the bearings and all wear surfaces and transfer heat out of the transmission and into the radiator and air coolers. The fluid must be circulated any time the engine is turning the torque converter