Tap into trans. line to change fluid?

[falcon556]

So I'm bored and decided to do some math....

I heard of people draining the pan, refilling it, driving for a few days, draining the pan, refilling it, driving for a few days....etc....repeating this cycle until they go through a whole case. I guess they don't want to tap into the lines and don't want to pay for a tranny flush, but want to get all the fluid replaced.

The problerm is that you get less and less of the old fluid out of the tranny everytime you repeat the process. I think the FSM says an empty tranny takes 8.45 qts and assumimg each pan drain gets 4 qts out, here goes the math:

First change gets 47% of the old fluid out (4/8.45).
Second change gets you out 69% of the old fluid (0.473+0.473^2).
Third time is 80% (0.473+0.473^2+0.473^3).
Forth time is 85%.
Fifth is 87%.
Sixth is 88%.
Pointless to do anymore change at this point.
​

So going through a case (12 qts = 3 changes) gets out 80% of the fluid, which is probably fine. I was just thinking about this and wondering about the math.

Tap in to the lines and you use 12 qts and 100% new fluid.

 

[Thayer]

Tap in to the lines and you use 12 qts and 100% new fluid.

Yep, that's what I said I did. Just doing the math for people who decide to go the other route.

 

[BrettM]

I put synthetic in mine when I did the swap and then found out the AW4 doesn't like synthetic. Pulling the pan plug (drops 3 quarts) and filling through the dipstick tube really isn't hard at all. I did that like 4 times with starting the engine in between so everything would mix.

 

[DJ404564X4]

i went to the dealership and bought two of these...

 

[DJ404564X4]

pulled both lines..
replaced the old push and pull "inserts"????

replaced the front trans cooler line, and ran a hose to the rear return line. had the wife start it in park, waited for it to drain down. did that three times, four quarts each

was amazed the differance it made.

 

[Dobbs]

I have rebuilt alot of auto trans over the yrs .the only ploblem with doing this is the Filter is still dirty. And you wont belive whats in the bottom of the pan if it has a lot of miles on it the best thing to do is flush it and drain it and change the filter drain the converter tone thing about removing the pan you can see if any cluches are comming apart small pc will be in the bottom of the pan a long with any metal pc .

 

[DJ404564X4]

I have rebuilt alot of auto trans over the yrs .the only ploblem with doing this is the Filter is still dirty. And you wont belive whats in the bottom of the pan if it has a lot of miles on it the best thing to do is flush it and drain it and change the filter drain the converter tone thing about removing the pan you can see if any cluches are comming apart small pc will be in the bottom of the pan a long with any metal pc .

my bad, i'd already done that and simi flushed it with factory ATF.