The theory is based on how dirty the transmission fluid is. If it is extremely contaminated, new fluid will flush it out and become dirty itself very quickly. This can lead to it slipping. Simply, you have removed a portion of the debris that was helping with friction between the clutch plates. The new fluid does have a detergent in it, so it will start cleaning.
However, in most cases, it doesn't cause this to happen. If it is shifting hard, chances are there is a restriction in the filter or transmission causing the line pressure to lower. That can eventually lead to the clutches failing.
How dirty is the fluid in it presently? If you were to describe its color, what would it be, black, red, or dark red? Was the fluid ever changed in the past?
Let me know.
Tuesday, June 7th, 2022 AT 8:51 PM