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I know that you cannot tow a vehicle with an automatic transmission the same way as a manual. This is because the automatic transmission will not be properly lubricated.

I read in the comment to this answer that the torque converter pumps the oil to lubricate the automatic transmission.

I read in this answer that manual transmissions on the other hand are lubricated because the lower gears are sitting in the oil and spread it around and that the fluid actually fills up around half of the transmission.

So my question is: Why can't automatic transmissions be lubricated in the same way as manuals?

EDIT: I dont feel that this question answers mine. It has to do with towing and the reason automatics cant be towed like manuals is because the engine is required to lubricate the transmission. So I guess what my question comes down to is, is is there a reason automatics need the engine to lubricate them rather than simply being surrounded and lubricated by oil like a manual? If not, why are automatics lubricated the way they are, requiring the engine to be running?

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Because they are very different.

A manual transmission is basically just a bunch of gears, shims, shafts, and synchronizers bathed in oil that gets swung around by the gears sitting in the oil.

An automatic transmission is hydraulically controlled and is full of valves, tiny passages, gears, clutch packs and many other things. For any of these to work they need hydraulic pressure provided by the oil pump (driven from torque converter and hence engine). Some automatic transmissions may be fine being towed but this depends entirely on what is spinning and making contact when there is no oil pressure in the transmission. I.e. if there is just a shaft spinning on a bearing it's probably fine since there is no load, but if there are other things connected that are making contact with each other (like a journal bearing or etc) then it will wear out because there is no oil pressure.

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  • +1That makes a lot of sense, I didn't think about all of the other parts involved besides the gears. – J-Rome Oct 14 at 13:27
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The shafts and cogs in an automatic may be placed above the sitting transmission oil level or obstructed from splash lubrication by shield, guards, electronics, any other equipment and thus depend on pressure from oil orifices pumped by the torque converter.

Note also that some 'Automatic trigger manual' like Honda high RPM, motorcycle style hydraulic operated blocking ring and 'automatic synchromesh' design depend on a separate pump even though really their cogs and shafts are below the sitting line and will be splash lubricated. So an exception may be made for Honda.

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  • I see, so you would say that in an automatic transmission there are too many mechanicals in the way to allow for splash lubrication – J-Rome Oct 13 at 13:07
  • that is my contention, look at the diagram, look at the way the external belt driven clutch packs can be placed nearly underneath the shaft, leaving them only room in the middle of the case. – Andyz Smith Oct 13 at 13:46
  • except in a honda, where the shafts are nearly similar to a submerged manual or an integrated wet clutch motorcycle transmission. – Andyz Smith Oct 13 at 13:47
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Classic automatic transmission (torque converter) is not just different from mechanical gearbox, it's entirely different concept. While gearbox is gears connecting 2 shafts and being lubricated by oil, torque converter is oil. Literally, the energy from engine to wheels flows through oil, oil that's energized by the impeller and working against turbine.

Therefore, there is no question of "lubricating like manual". There is no "lubricating flow" in the torque converter, there is only power flow, which happens through the oil.

Also, I believe there is misconception that the damage comes from "dry operation". It doesn't, the bulk of damage comes from the converter being operated "wrong way" and "idling". When engine is idling and torque converter is in stalled condition, the transmission heats up a lot, but the running engine provides coolant flow. When towing, the heating is much worse, all the forces are acting wrong way - and the cooling is not working. The damage is thermal. (If you idle a lot in gear, it also damages the transmission)

Most automatics CAN be towed without damage: just not fast and not far.

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