Re: coasting in neutral

I appreciate all the excellent replies from everyone. Thanks for all the 
info, it has been really great.

The reason why I wonder about this (and why it is a benefit to me) is that 
I drive a 1983 MB 300D-turbodiesel. The car has more or less the 
aerodynamics of a brick, but it gets me 30MPG in comfort, so all is well, 
IMO, especially when I use biodiesel and vegoil in it. Anyway, down this 
one side of a bridge I go over, there is a nice long downgrade, then a 
short straightaway with slight hill, and then a tollbooth. If I let off of 
the throttle at the apex of the bridge (at 55mph), and go down with the car 
in gear, Ill decelerate to 35 MPh by halfway down the bridge, and be at 
idle speed by the tollbooth. It has that kind of drivetrain losses.

If I shift into neutral at the bridge apex (at 55mph), I coast down staying 
near the same speed all the way down the bridge. I then slowly approach 35 
mph when the speed limit drops from 50 to 35, approaching the toll booths, 
and am at about 20 at the toll booth. At that point, nearly fully stopped, 
I shift into drive and go off again.

I am not dragging pads on any of my 4 disc brakes, I use synthetic diff oil 
and MB ATF. There is just a lot of drivetrain loss, and so for me it is 
seemingly economical to coast down the downhill, rahter than adding a 
slight throttle to keep the speed constant going DOWN a rather steep 
incline.

Thus my question.

I am glad that I most likely didnt harm much by doing it (yet), but I have 
started leaving it in gear on the way down... I dont want to wear clutch 
packs or cause insufficient lubrication by the time 1/2-3/4 mile rolls 
around at the tolbooth.

So any other comments would be great, and otherwise, thanks very much for 
the info!

JMH

>
>
>Coasting with an automatic will not usually offer any gain
>over just letting it do it's job.  This will cause more wear
>on the selector system any may very well produce additional
>wear on the forward clutch pack because of the additional
>application cycles - many late OD transmisions usually keep
>the forward pack engaged at all times when a forward
>position is selected.  There may also be some reduced
>lubrication to some parts of the trans because of the engine
>operating at idle.  Also, it is not legal to coast in
>nuetral in many states because of the lack of engine braking
>control and additional load that may be placed on the
>brakes.  The best thing to do with an automatic transmission
>is to leave it alone to do it's job.  Engineers have been
>paid many millions (billions?) of dollars to figure out how
>to make it work reliably over many tens of thousands of
>miles.  Why second guess them?  You may also be interested
>to know that an automatic transmission has internal
>sacrificial materials designed to wear out thus eventually
>requiring replacement.  This is the same concept as a clutch
>in a manual shift vehicle.  Either may very well outlast the
>vehicle or the owner with a little care and skill in
>driving.