On Fri, 31 Oct 1997 00:35:35 -0500 Nory@webtv.net (Nory) writes:
>While we're on the subject, why are you supposed to disconnect the
driveshaft when you're towing? I know you're supposed to, but I don't
know why.
When towing the car, the engine is presumably not running. The
transmission input shaft is then not turning, along with the lay gear and
all of the helical gears it is in contact with on the main shaft. The
rear wheels (on the ground) force the drive shaft to rotate, which in
turn rotates the output shaft in the gearbox. That is, the only thing
rotating inside the gearbox is the output shaft (and the speedometer
drive gear). There are no parts moving in the oil at the bottom of the
gearbox.
On the main shaft there are bronze bushings inside of the third gear and
the second gear (also the 1st gear in the case of a 4-syncro unit). MGA
1500 gearboxes also have a bronze bushing at the back of the gearbox to
support the drive shaft front yoke (maybe earlier models as well). These
bronze bushings do not like running without lubrication for extended
periods of time, and are at high risk of wearing out during a long tow.
>BTW, I've never seen the Triple-A guy do it......
Most tow truck operators either aren't aware of this problem or don't
care. Also most AAA tows are not for excessively long distances.
BTW, FWIW, I have on occasion towed an MGA for distances of 50 to 100
miles with the rear wheels on the ground and the drive shaft still
connected. And I have on later occasion disassembled the gearbox (for
other reasons) and found no noticeable wear on these bronze bushings. I
do hear other stories to the contrary, especially on longer tows.
Barney Gaylord
1958 MGA with an attitude
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