In a manual trans the gears spin around even when it is in neutral. The gears throw the oil around and oil the bearings, gears etc as long as there is oil in there deep enough to touch the gears. I have seen vehicles abandoned by the side of the road because the rear gears froze up, especially trailers made out of old pickup trucks. This will not happen if they have the right amount of oil.
It depends on the trans design. On constant-mesh trans, as long as the input shaft is turning, you've got lube because of splash lube from the cluster gears. But with the motor off, the cluster gears aren't turning and neither is the other gears on the main shaft. The shift hubs are turning because they're coupled to the shaft, the gears are floating on the mainshaft. If the hubs are picking up lube and splashing it around, you're OK. If not, you'll take out the mainshaft bearings and maybe the bushings in the gears. Distance/speed enters into it also, most manual trans can be towed a fair distance before this become an issue.
Here's a cutaway view of a 39 transmission. When in neutral the top shaft, the main shaft, which is also the output shaft, will spin when the car is being towed. 2nd gear is not engaged to the output shaft when in neutral, so it will not spin. However, Low/Reverse is, and it will spin with the output shaft. If it was synchronized, and constant mesh like 2nd gear is, it wouldn't spin with the output shaft either, but in this case it will. So it will throw oil up on the output shaft bearing and lubricate it.
If the oil level is at the filler plug, the whole transmission will get will get lubed by slosh and oil drag when towing on the ground. I have towed on the ground to Bonneville (900 miles one way) more times than I can remember and to California for sprint car races in the old days and never had a transmission problem.
I know in most states the car you are towing has to be registered and insured. That being said, I would rent a car trailer from one of the rental companies and a truck if you don't have one. With the crazy people on the road today, it would be the safer thing to do. KK
Ok take a old 318 chevy three speed. second gear at the rear of the case spins on the tail shaft however the syncro assembly does not spin on the tail shaft. and first and reverse sliding gear doesn't spin on the syncro assembly. I just went out and pulled the fill plug from a 318 Muncie. put it in neutral and turned the tail shaft. the first and reverse sliding gear turns in neutral you can not stop it with a screwdriver put against it thru the fill hole. if you jam the screwdriver blade between the gear teeth you cant turn the tail shaft. The first and reverse sliding gear gear the bottom is below the oil fill level. Im convinced that gear will be slinging gear lube when the tailshaft is turning and it is in neutral. So Im of the opinion you cant hurt a 318 Muncie by flat towing. Ive got a torque tube ford trans somewhere. when I find it I will check it out and take pictures and find out for certain?
not me and Ive flat towed a great amount. I have disconnected the driveshaft on automatics. like C4 fords and other that did not have a rear pump. If its a automatic that cannot be push started you need to disconnect the driveshaft.
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