This is an old thread, but I wanted to add my 2 cents.
The differential really does not care which way it turns, and there is so
little torque passing through it when the vehicle is towed that it is not an
issue.
The real concern is inside the transmission.
Theo nailed it, the gears are not turning as they are when the vehicle is
driven by the engine.
Most old design transmissions do not have any oil pump and do not use
bearings between the mainshaft and the gears.
The steel gears spin on the steel mainshaft with a nice coating of gooey 90
weight gear oil in between.
The problem comes in when the input shaft, splined to the clutch, does not
move.
Now the countershaft, geared to the input shaft and down below it in a
puddle of gear oil, does not spin and thus does not throw gear oil all over
the place.
The mainshaft and gears, above the countershaft and out of the gear oil, do
not get lubrication.
The gears are held stationary by the input shaft and countergear, and the
mainshaft spins inside the gears with little or no lubrication.
Some transmissions will survive this abuse, but others will not.
I have seen a T-5 in a new GMC S-10 that was completely destroyed by towing
the truck behind a motor home.
The safe way to do it is to disconnect the driveshaft.
If you take the shaft out, plug the end of the transmission to keep oil in &
dirt out.
This leads to question 2; what the heck does it matter if the driveshaft
goes back in the same position?
In a perfect world it does not.
However, in that we do not live in a perfect world, there probably will be
slightly different vibration characteristics with the driveshaft installed
in different positions.
One of the first things done in attempting to eliminate drivshaft vibrations
is to turn the shaft 180 degrees at the rear axle flange, in the hope the
flange is off center slightly and the vibration will be eliminated.
Sometimes it works, sometimes it does not.
Happy Motoring
Doug Leithauser
ASE certified Master Technician for 20+ years
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