Why is towing a manual transmission car, in neutral, with the drive wheels on the ground, considered safe?

Question

It is clear that cars with automatic transmissions cannot be towed with any drive wheels on the ground, engine off, in neutral, because the torque converter powers the lubrication pump for the transmission.

Why is it considered safe for a manual transmission? Doesn't the transmission need to be lubricated and cooled, just like an automatic? What about the differential or all the other parts of the car that move while being towed? Don't they need to be properly lubricated too? What is the technical reason behind this?

Edit #1

I thought that for a manual transmission in neutral, the output shaft does not spin the layshaft, which in turn does not spin the crankshaft, otherwise the entire powertrain would be 'closed' or 'connected', so how is it possible that splash lubrication is occurring at the bottom of the sump?

Why was the method for supplying lubrication to an automatic transmission engineered differently compared to a manual transmission?

Answer 1

Manual transmissions (most, but not all) lubricate not through a pump, but through the action of the gears and secondarily through the level of the transmission fluid itself. In some transmissions, the lower gears in the transmission, which touch the pool of fluid at the bottom of the transmission, transfers fluid through contact to the upper gears. In this situation, since the output to the drive axles is still attached to the gears, even when the transmission is in neutral, the fluid still flows.

EDIT: Checking through many different transmission layouts, it also become apparent the level of the fluid is high enough to be right at the level of the main shaft in the transmission. In some transmissions where the lay shaft (as @Narcotixs pointed out) doesn't have gears actually turning, the amount of transmission fluid in the gear box allows for the lubrication of any moving parts.

This representative image (sorry, best I could find on Google) shows the location of the fill plug in relationship to the main shaft. Most manual transmissions will have this same relationship between the fill plug and the main shaft.

/EDIT

The differential is much the same as the ring gear sits in the gear oil and the oil flows through differential. The differential doesn't care so long as the tires are moving. It will behave the same either way, whether there is power applied from the engine, or the tires are just rolling along.

That being said, putting a car up onto a tow dolly or trailer is a much "safer" way to transport a vehicle. It will be much more secure, especially if you're looking to transport the vehicle for any longer length of time.

Answer 2

Because, in a manual gearbox (those that I am aware of) the method of lubrication is by splash as the layshaft sits in the oil, so there is no engine driven pump connected to the input shaft.

Same argument for the diff - splash lubrication.