elektrinis

After some thinking and playing around on CAD, this is what I came up with: This is a dual lobe pump. One pump gets old ATF from cooling return line and dumps it in to an empty bucket. This pump works as a hydraulic motor, driving second pump. Now that second pump sucks on fresh ATF from another tank and feeds it back in to return line of AT. The beauty of it is that constant oil volume is maintained during flush and the process is not interrupted by stopping refilling quart by quart (which leads to mixing internally). Would this work reasonably well? I have access to some machinery, could throw a prototype rather quickly.

Thanks Dave, this document is very detailed. I see there are multiple sump dumps all around (marked with X), however it is not clear to me how is pressure regulation and torque converter arranged. I don't see the overflow from pressure regulator going to torque converter, the return is directly to sump. And torque converter is being fed by line pressure?? Lock up valve looks quite complex and difficult to understand. Does subaru 4EAT have a lock up torque converter? What are the differences of MPT and VTD (I googled the definitions, but no idea), and how do I know which one is mine?

Not in this case, at least not in car's service manual. Maybe separate manual is available for the 4EAT? Anyone have one available?

OK, that is interesting and sounds reasonable. I knew there is something wrong with that diagram. Then the question is... How much flow do we have on regulated line when no shifting is happening? I guess it's static more or less, just as much as leaks out through various clearances, which should not be too much? Can we pin a number on that, like 2%? And when shifting, it empties the cartridges and valves by simply dumping the oil in to pan?

Okay, multiple returns is an issue... I did not take such gearbox apart yet, so no idea what the actual path of ATF is. And if it is more or less similar on most ATs. Was under impression it goes something like this: Pan -> pump -> torque converter -> valves and everything else -> cooling -> pan. Saw some videos of people attempting DIY flushes and dumping the fluid from cooling line. The flow seemed quite near to what one would expect from integrated displacement pump running at idle RPM though. Let's check: A volume in one tooth is roughly 2ml, times 9 teeth, times 700 RPM = 0.2 liter per second = 1 liter in 5 seconds, or full 10 liters in 50 seconds. This is roughly the figure various youtubers are getting to dump all of old ATF. So an assumption can be done that near to 100% of pumped oil is going a full circle through radiator. Would be great if someone could correct me on this. What's the actual internal path of ATF? EDIT: This is interesting: http://www.sonnax.com/articles/124-anatomy-of-a-transmission-oil-flow-in-the-pump-pr-converter-cooler-lube-circuits So it seems I did not get it totally right, ATF from torque converter goes to cooler and only then to gear train. I can't believe the cooler is under such high pressure (required for gear train). If it is as shown however, I wonder how much ATF is trapped in gear train when in neutral?

Yes, I am sure I am checking correct dipstick... Oil in front diff is much thicker. Will drive around with OBD connected to check temperatures. That is alarming though... Just contacted previous owner and he says he never did anything to the AT (no oil changes). If it's really cooked, but gears are not slipping, so likely it was towed incorrectly and that lead to overheat? About the return line. Isn't it going directly from radiator to pan? In this case I guess it will not suck any fluid back, unless you make sure dipstick (and breather) is completely plugged to create vacuum?

Hmm.. Heard of this method, sounds bit time consuming. I was thinking of some kind of bidirectional pump... Outgoing ATF drives a hydraulic motor, and the motor drives a pump and pumps exactly the same amount of fluid. So ultimately you would maintain constant level of fluid during the procedure. For example: Such pump should be fairly easy to do... Procedure for full 100% flush goes like this: 1. Drain the pan 2. Change filter(s) if you like. 3. Add the same volume of new ATF as drained. 4. Disconnect radiator return line from the transmission and connect it to OLD ATF IN port of the device. Connect a hose from OLD ATF OUT port to an empty bucket. 5. Connect NEW ATF IN port of device to a tank with fresh ATF, and the NEW ATF OUT port of the device to return port of transmission. 6. Run the engine and watch. Slowly go through gears in meantime. Stop the engine when you see bright red (fresh) ATF going out, or when your tank of fresh ATF runs out. Would this work?? I have access to some machining toys... Could do a prototype in a few days.

I have an Impreza 2.0L 4AT 2008 at 100k mark and the gearbox is acting up: slow to shift, rough shift, vibrations on D when stopped. Inspected the ATF, level is good, but color is weird: clear, slight yellowish, almost just like fresh engine oil. Likely wrong oil was replaced by someone before me. Also manual states that vibration can be caused by higher viscosity ATF (dexron III instead of VI). The manual also list possible mechanical issues causing the delays, but let's try flush first. I know there are different opinions, flush vs. drain, let's not discuss that here. I decided to do a full flush. Now I was searching the internetz how that could be DIY'ed... And oh man, some people are brave. In other words, I did not find a safe way this could be DIY'ed without fancy flush machine that only large specialized shops have. Did I miss something? Was even thinking about making a special pump myself.