Re: [A/S] Towing Question

["Jim Dunmyer" <jdunmyer@xxxxxxxxxxx>]

Jim,
 I believe your owner's manual tells you to tow in Direct, NEVER in OD
(4th). The reason is that when the trans shifts to 4th, the main line oil
pressure drops off and is adjusted by the throttle pressure. (more throttle,
more pressure). The reason for this action is to give smoother shifts. BUT:
the lower line pressure will allow clutches to slip under heavy load; this
will be much worse with larger engines because they don't need as much
throttle to haul the load, thus allowing line pressure to be 'low'. When you
select Direct in your transmission, the line pressure is forced to "max",
thus preventing clutch slippage.

When the TCC (torque converter clutch) locks up, the oil continues to
circulate, as the pump is coupled mechanically to the engine. Of course,
that low line pressure (see above) can cause the TCC to slip, eventually
burning it up. I don't know for sure, but I'd bet that the TCC will lock in
3rd IF "Direct" is selected on your shifter. It will not lock if the
transmission has simply downshifted because of load, causing excessive heat.

Remember that a slipping clutch(s) in the transmission will cause excessive
heat, but you won't see it on your temperature guage until it's way too
late. The temperature rise seen on the guage is due to an unlocked converter
that's working hard. Uphill, downhill, or backing up will cause the
temperature to rise very quickly.

You're correct about shifting to Neutral at the side of the road. Many
transmissions (I'm not sure about the 700R4) don't circulate any oil through
the cooler loop when in "Park", so you'll get very little cooling.

If you're really interested in seeing how the pressure changes in the
transmission, get a guage and appropiate tubing to connect it to the port on
the LH side of the transmission, very near where the shifter lever is
attached. The guage should go to about 300 PSI, as the normal line pressure
is 180, IIRC. You want the tubing to be long enough that you can have the
guage in the cab while you go for a drive.

                                                                  <<Jim>>