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Re: [Shop-talk] An off shoot of the Toyota debacle.....

To: "shop-talk" <>
Subject: Re: [Shop-talk] An off shoot of the Toyota debacle.....
From: "Mullen, Tim (IS)" <>
Date: Thu, 4 Feb 2010 15:10:48 -0600
Arvid Jedlicka Wrote:
> Just curious, if it is only on the output side how do you ever get it
> to do anything?
>The pump would not be turning if the car is not moving and I can
> only assume that if the pump is not turning there is no pressure
> available to engage anything to get the car moving. I must be
> missing something here ...

The pump (in the transmission) is driven by the engine under normal
circumstances.  Start the engine and it turns the input side of the
transmission which turns the hydraulic pump.  With the pump turning,
there is hydraulic pressure that allows you to "put it in gear".  The
pump is driven from the input side of the transmission.

If the car is moving and you shut off the engine, the transmission is
still "locked in gear" (because it had hydraulic pressure) and the
output side of the transmission can operate the hydraulic pump and
continue to turn the engine over (the input and output of the
transmission are locked together).  Once you put it in neutral (with the
engine off), the input and output are no longer locked, and the input
side stops turning - and the hydraulic pump stops pumping.  Now if you
put it back in gear, it won't turn over the engine (or the pump) as
there was no hydraulic pressure to keep things "locked".

Tim Mullen

Chantilly, VA
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