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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 11:16:59 -0600
Nolan wrote:
>> Someone suggested that if you left the car in gear after you turned
>> the engine off that the transmission would turn the engine over
>> to keep the power steering and brakes working.
> Only a manual transmission does this.  Automatic transmissions
> disconnect because the engine is what drives the hydraulic pump.
That was me.  And I beg to differ with you about the automatic.

Yes, if the car is not moving then the transmission can't turn over the
engine - that's why you can't push start an automatic.

However, the engine turns over the hydraulic pump in the transmission.
Once that is pressurized, and the car is moving, the transmission is
still coupled to the engine (through the torque converter) - as long as
the car is moving, there gears are still engaged, and the pump will be
turned.  It will keep the engine connected to transmission as long as
the car is moving (at least a little bit), and you will continue to have
the engine turning the power steering pump.

> Simple test, turn the ignition key back on.  If the engine is still
> spun over, it will instantly begin to run.

Done this many times.  It works just fine (although it may not be good
on the engine).

> Try your test again at 70 mph, and try to bring the car to a complete
> and total halt.  That you will find to be quite different.  Now
> make the mistake many people make, and try to "control" the
> vehicle instead of simply stopping it immediately.

And that last sentence is the important part.  Most any car out there
should be able to stop from 70 mph at WOT.  If the person actually tries
to stop it instead of trying to slow it down and control it.  One stop -
yep.  Drag the brakes for a few miles - nope.

Tim Mullen

Chantilly, VA
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