I wrote in another threat but i will repeat:
I overhaul automatic transmissions in Germany and can tell you from my experience:
Oil in an automatic transmission should be changed at least every 70,000 km (43,000mi), under heavy conditions e.g. in frequent trailer operation also earlier.
The following is the background: The lubricating effect of oil is created by long chains of hydrocarbon molecules that slide past one another. In an automatic transmission, these molecular chains are subjected to high mechanical loads and break. The oil loses its lubricity and hydraulic stability over time. This is often reflected in poorer or rougher gear shifting behavior.
From a certain level of oil wear, the automatic transmission also wears out more.
And i state: Next to not good use, like permanent kickdown, or switch to neutral at the traffic light, or not to warm up the transmission before excessive acceleration, deferred maintenance, in form of oil change are the most common reasons, why automatic transmissions fail too early.
Many are afraid of an oil change at a transmission and refrain from it. That's wrong!
It is absolutely not necessary to open the unit and replace the automatic transmission filter every time, because in an automatic transmission there is neither so much abrasion, nor so many lumps that the oil filter would become clogged. And if, your unit is near the end.
So it is absolutely enough to change the filter all 2 oil changes, or even never.
Better you change your oil all 20.000mi without change the filter, than after 100.000 miles, before an overhaul, because someone tell you: That is the last thing you can try..
Therefore, you can change the oil quite well with this method:
https://www.cadillacforums.com/threads/transmission-fluid-change.154002/
This flushing is better than just draining the oil, because at least 2/3 of the oil is in the transmission and not in the oil pan. It is in oil passages, pistons, torque converter, oil cooler of the automatic transmission located. This oil you don't get out of your unit, when you just take the pan off.
That's why some workshops offer expensive gear oil flushes, which I don't think make any sense, because they are expensive and you can do it yourself.
Even a layman can do that. Just these three points are important!!!:
1. Use the right automatic transmission oil for your unit, with the right specification for the gearbox. As far as I know, on GM vehicles like Tahoe and Escalate, that's Dexron VI.
2. It is essential to ensure that no foreign particles are introduced into the automatic transmission, so ensure absolute cleanliness when filling.
3. And definitely pay attention to the correct filling quantity, which is relatively easy with the method I linked. When you have changed the transmission oil, the transmission has to be warmed up properly by driving, and then the automatic transmission oil level must checked with the engine running in P on a level surface.
If you do this method and watch the 3 points, it's not magic at all.
And additional to the often heard problems after flush i state:
From my experience, unit dies because of worn out clutches, brocken parts, destroyed gears, or in case of the Tahoe and Escalate (2000-2006) gearboxes, worn out valve blocks.
The background that people tells that after a flush the unit dies is for sure the result of people with units go to their mechanic with bad shifting behavior. Their gearbox simply starts to have problems at some point, because it's worn out, probably advantaged of the old oil. They describe their problems and the mechanic says: "We can try to make an oil change, that can help. Because experience is that very old oil makes a bad shifting transmission."
Then they make an oil change, but the gearbox dies shortly later, because it was just worn out.
And then some people infer "that fresh oil destroyed a gearbox".
That is simply rubbish...
I would like to end with a quote from the famous German rally driver Walter Röhrl, who once rightly said:
"Cars cannot be treated like people, cars need love."
In this sense: Have fun with the smooth shifting behavior after an oil change and the good feeling that you did anything to service your unit, to keep it in service for a long time..
