ATF Changing Logic:

[ctechbob]

That mechanism reduces pressure to some predetermined value. If the pump pressure is below that there is trouble in River City.

Speaking of. I never gave much thought to line pressures in a transmission.

Precision Transmission just uploaded a video of a 4L60E going through the gears with a pressure gauge connected. It really pumps the pressure up right before a shift and then drops it back down, pretty interesting dance it does:

 

[4WD]

I pull and replace three quarts a year and yes the old Dexron 6 is always darker. However, I find the magnet in the pan is coated with particles when I drop the pan every 50,000 miles. I’ve opened up a tranny filter that was in use for 5 years and found only a few metal particles in it and nothing else. YRMV.


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I put in a B&M drain plug during first drop … and can swap 6 quarts every Spring (6L80e)
Funny we always took for granted the “hot level” etc on a real dipstick and easy fill tube …
I just dread the 1st time with my Mopar … although you ain’t gonna find me with a laptop under a Jeep … think it works Ok with a digital meat probe

 

[Hall]

and yes the old Dexron 6 is always darker

Not surprising. GM and Ford developed a family of transmissions as well as a fluid for it (Dexron VI / Mercon LV) and Mercon LV is known to get dark very, very quickly. Someone posted a bulletin from Ford's engineering group advising technicians to not use the color of the fluid as an indicator of its age, condition, etc.