Re: [A/S] Re: Dodge diesel with standard transmition.

["Jim Dunmyer" <jdunmyer@xxxxxxxxxxx>]

Kerry,
 There is no general rule, each transmission is different, even within a
given manufacturer. Your owners' manual should tell you what is correct for
YOUR vehicle and transmission.

Many automatic transmissions control the main hydraulic pressure in the
transmission (they are all hydraulically actuated, you know) by the throttle
pressure. Light throttle -> lower pressures; this is to give smooth shifting
by allowing the clutches to slip a bit as the various gear engage. When you
have a lot of throttle on it, the pressures are increased to prevent
slippage when it shifts.

On SOME transmissions, when the thing gets into "High Gear" (overdrive,
usually 4th), and you back off on the throttle as you get up to speed, the
line pressure drops off. This can allow the clutches to slip if the load is
heavy, such as when towing a big trailer. Slipping clutches will
self-destruct very, very quickly, you'll not be able to detect the problem
on your transmission temperature guage until it's way too late.

On transmissions such as above, the line pressure is kept at "maximum" when
the transmission is prevented from shifting into O.D., so the clutches will
not slip. Such transmissions normally WILL allow the torque converter to
lock up when the vehicle is up to speed.

The manufacturer has a vested interest in keeping your transmission alive
and will always have instructions in the manual telling you what they
recommend. Of course, YOU own the vehicle, so YOU can damn well do what you
please, but if you think you know more than the engineers who designed it,
you're kidding yourself. They don't always tell you WHY they recommend a
specific action, but you really should mind what they say.

My 3/4-ton Dodge with the 47RH transmission is OK to tow in O.D., from
everything I can find in the manuals. The other Dodge truck's manual
(1/2-ton truck) was quite specific about pushing the "O.D. Lockout" button
when towing, so I always did so.

Again, there's little sense in discussing it here, everyone needs to RTFM
for his/her own vehicle.

                                                        <<Jim>>