High mileage transmission that’s had no pervious service

My 2007 Tacoma has 259,000 miles on it. My 2009 Honda has 230,000 miles on it. My 2020 Explorer has 82,000 miles on it and the F150 I traded off 2 weeks ago had 165,000 miles on it. That's over 700,000 combined miles on factory fluid. In fact in the 50 years I've been driving I've never once changed the transmission fluid in anything I've ever owned. Never had a single problem in several million miles.

The local transmission shop tells me that they have customers who insist on changing the fluid every 30,000 miles and others who drive it till it dies. They end up rebuilding or replacing them at about the same miles. And the number of miles varies a lot depending on the vehicle. Some cheap econobox cars with CVT transmissions are good for around 150,000 miles. Certain vehicles and model years have known problems and die at 100,000-150,000 mile. Often the same vehicle, with the same transmission, but a different model is known to last 400,000+.

Tacoma are regularly getting 400,000+ miles out of the transmissions whether they change the fluid or not. If you pay to have it replaced every 30,000 miles and put 400,000 miles on the transmission before it dies you will literally spend as much servicing, it as it will cost to rebuild it. And Tacoma transmissions can be rebuilt just as good as new for a lot less than buying new. Other vehicles can't be rebuilt, you just have to replace it.

At this point your transmission is either just fine, or near the end of its life. Either way changing it now isn't going to help anything. And if it is near the end of its life keeping the old fluid in there will buy you some time. As the clutches wear the abrasives on them comes off and is suspended in the fluid. The fluid is no longer as slippery as when new and that helps the clutches. New fluid is actually too slippery in an worn transmission and the clutches slip. They are going to completely go soon either way. But new fliud in a worn transmission usually results in it becoming unusable within days.

The difference between old school vehicles and newer ones is that 100,000 miles on a transmission was a rare occurrence years ago. Nobody would touch one with over 100,000 miles because they knew it was a waste of money. Newer vehicles last a lot longer. But the same advice still applies. If it's almost gone, changing the fluid will speed up the process.

 

I do my own service work and the reason I went all those miles ( first time automatic vehicle ) without changing was a talk with a transmission guy 40 years in the business and he said don’t touch it. The 24,s had some issues and my thinking might change when I reach 35k
We’ ll see if leave well enough alone when I reach it

 

Changing the fluids on old auto transmissions used to be the 'kiss of death'.

On newer stuff, regular maintenance makes them last.

It also depends alot on how the vehicle is/ was used.

My $.02

 

i did a drain and fill at about 100k on my 2017
staring at 120k shortly.
ill say it made a slight improvement.