'71 TH400 Trans Fluid Change

[Charlie P.]

Does trans fluid go bad over time? My '71 has less than 1/3 of the recommended 24,000 miles for fluid change, but it is possible that the fluid is 33 years old. I would like to avoid dropping the pan, but will do so if it is necessary preventive maintenance due to the age of the fluid.

Thanks in advance for the input.

[Joe L.]

Re: '71 TH400 Trans Fluid Change

Charlie-----

Chevrolet recommended that the automatic transmission fluid AND the automatic transmission fluid filter be replaced every 24,000 miles for vehicles of your car's era with the THM-400 transmission. I would definitely agree and follow that recommendation. Use Dexron III automatic transmission fluid.

[Charlie P.]

Re: '71 TH400 Trans Fluid Change

Joe- I was aware of the mileage interval, but the chassis manual does not mention a time limitation, as with engine oil changes. Are you saying that even though fluid in car could be 33 years old, I still don't need to change until 24,000 mi? Car has under 7,000 mi. I am wondering if the fluid degrades over time.

[Joe L.]

Re: '71 TH400 Trans Fluid Change

Charlie-----

Any organic material will degrade over time. Of course, the substrate material that the fluid is made from is, likely, millions of years old from the get-go. But, it's refined into a product which degrades a lot faster than the substrate material from which it was created.

While GM didn't place a time limit on auto transmission fluid of the period, if it were me, I'd change it. If nothing else, you'll get the benefit of vastly improved automatic transmission fluid available today. Your car was factory-filled with Dexron transmission fluid. Dexron II followed and they're up to Dexron III today. Dexron III is what I'd want in any GM automatic transmission I owned.

[Gerard Q.]

What about Power Steering Fluid

Same year 1971, would the power steering fluid need to be changed. Is there a specific type that would be best to use.

[Patrick H.]

Re: '71 TH400 Trans Fluid Change

Charlie,

You "may" be able to remove the fluid through the filler pipe. I'd suspect that if you're inventive and use a suction gun and a smaller plastic hose, anything is possible. While not as thorough as dropping the pan, it would at least allow you to replace a good portion of the fluid. Since you're likely going for Bowtie, it's at least a thought.

Yeah, like you're going to drive it much anyway???

Patrick

[Joe L.]

Re: What about Power Steering Fluid

Jerry------

Power steering fluid doesn't have a recommended change interval. However, I recommend changing the entire system contents whenever the system is apart for component replacement. You don't need to get every drop out, just drain as much as you can with the system open and refill. With a 63-82 Corvette power steering system, one usually gets the opportunity REGULARLY for component replacement so, as it is, there's not much chance for the fluid to get very old and deteriorated if one follows my practice.

[Gerard Q.]

Thanks Joe *NM*

[Gary E.]

Re: Thanks Joe

If it were mine I would get it changed, after all remember that condensation from use will also be a contributing factor in the life of your transmission.I would take your car to transmission shop that will not only change what is in the pan but the get all the fluid out of the torque converter as well. Any good shop will have the equipment to hook up to your transmission and give it a total flush and fill that only draining the pan can't do,beside that I would use dextronIII and a new gasket which after all is the only thing your actually trying to avoid anyhow...but that is my opinion.