Re: [VAC] towing in overdrive

[Jim Dunmyer <jdunmyer@xxxxxxxxxxx>]

Scott,
 You said it all in the last sentence:

RTFM (Read The er, Fine Manual)

The GM 2500 series uses a different transmission than the 1500 series,
for instance. The former can use overdrive when towing, the latter
definitely cannot.

My Dodge Ram 1500 says to not tow in overdrive, period.

It isn't always a matter of the transmission's 'hunting' between
overdrive and direct when very small grades are encountered as some
people think. "I leave it in overdrive as long as it doesn't shift back
and forth too much." The THM 700 R4 that's used in GM's 1500 series
trucks drops the hydraulic pressure when the transmission shifts into
OD, which can lead to clutch slippage and transmission failure if you're
towing. When you lock it into Direct, the line pressure goes to max and
stays there, preventing clutch slippage.

That's the only transmission that I'm *really* familiar with, but
there's a good reason why many models of trannys have the 'no OD'
specification for towing.

                                <<Jim>>



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