A/T Flush method question

[AbbadonTD]

I have been told never to completely drain my torque converter or to 100% drain my transmission. Drop the ole pan, regasket, and add, around 70% of the fluid.

When I went to have the transmission drained and filled, they told me that they can now flush out the fluid at pressure, so that the converter and the transmission are never empty, but it can force closer to 95% of the old fluid out, and it is never actually empty.

This was not an available option until recently, so is this a good idea?

 

[ExplorerTom]

Never heard that about completely draining the transmission and the torque converter.

However, it seems like on high mileage transmissions (which I'm assuming yours is), flushing is riskier than leaving old fluid in there.

I did the drain and refill a couple months ago. I dropped the pan and changed the filter as well. Seems to be running fine.

How was this option not available until recently? It's my understanding that transmission flushing machines always forcibly pumped new fluid in which pushed the old fluid out.

 

[Flexpedition]

I think the word 'pressure' is what causes concern. My local dealer has a Ford "Rotunda"? machine that does pump, under pressure, new fluid into the transmission while the transmission pumps out, under the same amount of pressure, your old fluid. Its done at both cooler re-circulation lines for equipped vehicles. They remove BOTH lines and hook them up to the machine, so one side isn't forcing the other as mentioned. Caveat is I've not changed my Expeditions fluid, and there could be such a method or machine that exists that forces the swap, so YMMV.

Can't be but a few pounds of pressure. They certainly aren't using an old swimming pool pump that will surely blow out seals and whatnot.

Its a slow process, maybe half-hour - 45 minutes just to pump/flush the 10-12 or however many quarts are in there.

 

[Mediamonkey11]

Doing a flush is not a bad thing if maintenance has been kept up on it, and machines haven't changed in recent past form what I know, they've always tapped into the cooling lines, usually right at the cooler, and used pressure along with the line pressure from the trans pump to intercept the fluid path and exchange the fluid.

My question is why do you think you need to change or exchange it? Depending on what engine you have, you either have a full capacity of 16 or 19 qts IIRC. Dropping the pan and changing the filter only changes about 40% of the fluid if I'm not mistaken, and if your fluid is in decent condition and you're doing it just because or you don't know maintenance history, then just do a pan pull.

I don't like the flush as I've had it destroy an old trans on a lumina I had, then again I think older transmissions that were neglected are what gave weight to that ols don't flush saying.

 

[AbbadonTD]

I was getting that bogged down feeling in the transmission when towing after about 150 or so miles. I checked the level and the fluid was very dirty, so I figured it could use a flush.

I only know what they told me, but I had them do the old fashioned drop drain and fill for me. I know these people and they are good at what they do [specific people], and when I get a trans flush and fill, oil change, filters, top off etc for under 200 bucks, I said let the monkeys work! I usually take my cars in for fluids, since then I dont have to worry about spilling everywhere.

 

[Mediamonkey11]

Wait, you just said you had them do a drop the pan and fill, no flush, correct? Because it's never a good idea to flush a trans that's been left neglected.


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[AbbadonTD]

yeah, drop drip and seal and fill "flush" I wasn't about to make that decision there.

I bought this beast in the spring. I bought it from the parking lot of a gas station from some dude on craigslist, so I don't assume anything has EVER been done. It is at 152K, and the DMV agrees that I am the "second" owner. The guy I bought from never re-titled it, he had it for 2 months, and in CO, I was still able to register it and he technically never owned it. I do know that the plugs and such are good, because they are performance parts, so someone, at some point, replaced them. I also know the belt is fine, because a pulley was missing from the engine. Beyond that I assume I am factory and old.

 

[98EXPnSRQ]

I dropped the pan and changed the filter and refilled. Then I disconnected the trans oil line that came out of the radiator and put a hose on the end of it. I started the engine and let 2 quarts run out into a bucket. Shut the engine off. Put two fresh quarts back in. Repeat until the fluid coming out is clean. It took some time and if I remember right, it took about 16 quarts before it ran clean. That's the safe way to flush it. Just don't let the pan run dry.