how should it be done when you replace the trans?

compressed air?

 

Take the rear-most trans cooler line (return line) off the tranny, stick a rubber hose on the end of it, and start the vehicle allowing it to pump 2 gallons to flush your converter and lines. I used (2) 1 gallon milk jugs.

 

http://www.amsoil.com/faqs/faq8.aspx

This is the best method to use. Doing it this way, you know you are using the correct pressure. Many transmissions have been damaged by having a machine flush where the pressure was too low/high. You certainly don't want to used compressed air. I would also add a drain plug while you have the pan off, not to be used in replacement for dropping/cleaning the pan, but to make the draining cleaner and easier next time. I like to drop the pan and do a partial change every 25,000 and do the complete flush every 50,000. I've used this method a couple of times now and I'm sold on it. Here's a tip: Run your old fluid into empty gallon milk jugs that you made quart marks on so you can make sure you are adding new fluid at the same pace that the old fluid is being pumped out. If the fluid is old and discolored, you will see the exact moment the last of the old fluid is pumped out and the new fluid arrives.

 

Here's the shop manual method ...

Click Here

 

If you fill up two (gallon) milk jugs, you will have used the exact same amount required to fill one of these transmissions from "bone dry" status, therefore you would be completely flushed.

 

and this wont screw up your tranny? running it dry i mean?

 

I did it one gallon at a time. If you add 8 quarts and drain 4, you won't run dry. If you see it stop pumping into your milk jug, simply turn the key off and add tranny fluid. I've done several different vehicles this way. Never had a problem.

Probably if you were to run continuously after the flow of tranny fluid stopped, at some point you might hurt something, but just using sound judgement and watching what you're doing, you won't harm anything.

 

ah ok, i didnt notice the add while you do this sentance, i though it was jus tdraining the whole damn thing

 

The "add" portion is after you have drained your old oil out and changed the filter.

 

So you are trying to say the 4R100 only takes 8 quarts to fill it from dry>??? -Mat-

 

If you put fresh new trans fluid in, pump out 8 quarts into milk jugs (which is all old fluid), then put return line back on, top off the trans with more new fluid, you will have used up approximately 17 qts of tranny fluid (including the 2 qts used in the flush) which means you have completely replaced all the old fluid in the tranny with new fluid.

Make sense?

 

You still will have some old fluid in there.
I just misunderstood you and thought you were saying a 4R100 only held 8 quarts total. He wants to flush out the cooler itself, I believe he has a failed trans he is replacing. They sell cans of cooler flush, or if a shop is doing the trans swap, they should have the proper equipment to flush out the cooler. -Mat-

 

If he's replacing a failed trans, he needs to install an in-line filter to catch anything that may be left over that the flush didn't get. I believe this is what Ford mandates for a failed tranny under warranty. Cheap insurance.

 

SVT F15O:

I believe disconnecting the rear (return) line flushes new fluid through the pump, converter, cooler lines, cooler and out the return line and into the milk jug. Where's the left-over? If you're getting fresh new fluid coming out of the return line, hasn't it already passed through (thereby flushing) the cooler?

This is how I do it, since there is no drain plug on the converter.

 

BlownHatch, sounds like we do it basically the same way. The only difference I see is that I am more interested in keeping the amount of incoming and outgoing fluid consistently equal so the trans is never over full or under filled.