Originally Posted by clinebarger
Originally Posted by danez_yoda
The caution is a vaild one. If its black or very dark then the clutch pads are worn and the friction in the fluid is helping them maintain grip in gear. If you flush all of that out it may start slipping. Also if the transmission is full of crud, the new fluid with fresh cleaners could lift that crud and move it to a part of the tranny that may not like the crud and cause problems.
However, at 78,000 miles unless your truck was pulling hard loads, the transmission fluid should be fine (some browning but still pinkish) This is OK to change (drain and refill not a flush). 30k miles after that is a good interval.
A worn transmission is a worn transmission! Burnt friction material suspended in the fluid doesn't help clutch packs hold!
I've seen completely metal to metal clutch packs hold under light applied torque. I've had 4L80E's have a slow forward engagement & only slip while towing. Forward Clutches are completely smoked with no friction material left at all.
Amen. And if changing out the fluid and filter destroy the transmission, it was either not long to this world, or shot before hand. I heard people say their transmission was acting up several times, and they planned on having it serviced hoping to resolve the issue. 9 out of 10 times these vehicles were poorly maintained, and the transmission never serviced. Occasionally the service would help, many times it wouldn't and it would fail shortly after. Typically those were the people telling others servicing their transmission ruined it. They'd usually leave out the part of them having issues before the service, but were quick to blame it. But all along it was neglect that ruined it.