Originally Posted By: cp3
calvin1, how is sucking fluid out through the tube going to get more fluid? You wouldn't pull any from the converter would you?
+1 A fluid exchange gets ALL the fluid. Or virtually at least.You waste some of the new, though flushing out the old but you can minimize that by draining the sump and refilling it with fresh fluid first. I woulnd't do a fluid suck on a car that had a pan because you may be leaving a lot of junk on a magnet below, not to mention the pan filter.
As to trans damage, I can't speak to every trans out there. There may be some that could be harmed, but none I know about. I takes no more than about five minutes to do the job, or less, and I can't see that being much harm. The parts lubed are the ones normally in operation when the car is moving... eg the planetary gears. WIth the car just sitting there, it's pretty much just the front pump and converter, which are full of oil, and the input shaft to some point.
Some advocate running until the fluid runs dry and I would advise against that because there is a slim chance of damaging the front pump running it dry. That's why the best way, in my estimation, is to be filling via the dipstick at the same rate as it's pumping out, which, as I said before is < 1 GPM on most trannies and easy to keep up with. I've done it alone every time, but it wouldn't hurt to have a person in the driver's seat ready to shut down in an instant