On Thu, 4 Mar 2010 22:53:05 -0500, "Ed Pawlowski"
wrote:



"Twayne" wrote in message
My Buick can be shifted into any gear you wish at speeds over 45 mph. Of
course, nothing will happen. Shift to Neutral, you're still in Drive,
shift to Reverse, still nothing happens and you stay in drive. I know
because when I read it in the manual, I tried it.

What Buick is that? When I shift mine into neutral, it is in neutral, not
drive. 2001 LeSabre and 1991 Regal went out of gear. I did not try
reverse. .


At speed, shifting to LOW will not cause the transmission to downshift
on most current automatics untill the speed drops low enough that the
engine would not be over-reved to drive it in LOW, and the throttle is
depressed far enough to accellerate the engine to the speed required
to drive it at that speed in LOW. However, once it has shifted to LOW
it will stay there when the pedal is released. The downshift enable
speed may be slightly higher than the full throttle upshift speed, and
higher than the full throttle kick-down (passing gear) speed.
MOST will also NOT engage reverse above a programmed (and quite low)
speed, to protect the drivetrain from damage.
Shifting into NEUTRAL, WILL disconnect the drive. It MUST for safety
reasons, and by the very design of the transmission.
All current transmissions sold for highway use in North America have
a "manual valve" that puts the transmission into a controllable
condition so that the solenoids can apply or release the required
clutches to drive the vehicle. When the Manual valve is put in
neutral, no pressurized fluid is applied to the solenoids, so even if
they are applied, the transmission will not transmit power to the
output/wheels..
The hydraulic pressure is manually disconnected in both neutral and
park positions.

Some hydraulic transmissions on off-road equipment are strictly
electrically controlled (or at least were a few years ago) but loss of
electrical power dissables the drive completely.