David Massey wrote:
> The problem with using O/D in 1st and 2nd is that the engine torque
> multiplied by 2nd and especially 1st gear may be enough to overcome the O/D
> clutch causing it to wear and fail
There is also a much less spectacular reason for this.
The hydraulic pump in the overdrive that engages
the planet gears is driven at shaft speed, which is
directly related to road speed since this is
after the tranny.
The slower your car is going, the less pumping the
pump does.
Below certain speeds. (ie: in first and second gear)
there may not be enough pump pressure to keep the unit
engaged, and it will slip in and out.
Above a certain speed, everything is fine and the
excess pressure is vented off by a pressure valve.
--
Trevor Boicey, P. Eng.
Ottawa, Canada, tboicey@brit.ca
ICQ #17432933 http://www.brit.ca/~tboicey/
"It is the nuclear missile Harrod's would sell!" - Sir Humphrey Appleby
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