Allison newbie: tow/haul mode

[Ian7]

Hi, As stated before, I'm new to Allison's.
The owners manual is very vague on the tow/haul mode. Says to use it when towing heavy loads, but says nothing about what it actually does, and when. When I'm towing my 12,000# gooseneck I always have the tow/haul illuminated, but on a hilly road (think I-77 in WV for example for those that know it), do I need to do any more than just leave it up to the tranny to sort out when to shift as we inevitably slow down while climbing, or do I have to be ready to pull the transmission out of "D" and into 3 or 2 or 1, and when and why or why not?
Many thanks.

[DmaxMaverick]

T/H mode not only adjusts the shift points, it also locks the torque converter much earlier (20-25 MPH, 2nd gear). Unless you can maintain above 55 MPH with light throttle continuously, use T/H to prevent TC unlock and repeated "gear hunting", especially in rolling hill conditions. Briefly switching out of T/H above about 50 MPH at light throttle will force an upshift, and is OK if the power and load will allow holding that gear. Otherwise, allow the higher RPM's or get more power to hold it. Locking out OD is also helpful in rolling hill conditions, as it prevents OD for the brief periods it will use it.

[Ian7]

Thx Dmax, but your answer sounds like I worded my question badly. Sorry, I'm not suggesting pulling the tranny out of "tow/haul", I always tow with it on, I was wondering if when laboring up a steep climb if I need to pull the tranny out of "D" into 3 or... or just leave it alone and let the Allison take care of it no matter how low our speed drops? thx.

[DmaxMaverick]

If you are unable to maintain speed, it should downshift, automatically. Pulling it from D to 3 will bypass direct (4th). So, if you are in OD and begin to slow, going to 3 will hit the redline, and may buck quite a bit. I suggest leaving it in D, lock out OD as necessary, and let the computers do the thinking. If it lugs, it will downshift. If the pedal pressure is too light, it will happen later, but you will slow, quicker. If you want to maintain speed, lean into it early (anticipate), let it shift as conditions require. If you delay shifts and slow down, it will still downshift. Downshifting a little early by increasing pedal pressure earlier, helps to maintain speed. If you are on cruise, it doesn't hurt to "help" it a little, in anticipation of a grade or hill.

[rapidoxidationman]

I force the issue on downhills by dropping down however many gears is necessary to maintain my speed with a minimum of brake input. a torque converter that is locked up thanks to the tow/haul function will also not generate as much heat due to fluid friction.

[Ian7]

thx guys, much appreciated.
I''d already figured it seems to prefer being in 'manual' mode while on the long ups and downs, I'm only in cruise control on the flats.

[Defender]

Tag along question.....will the Allison "braking" work whether O/D is on or off? Either way? Of course I am in Tow/Haul.

[DmaxMaverick]

Tag along question.....will the Allison "braking" work whether O/D is on or off? Either way? Of course I am in Tow/Haul.

Yes. T/H engine braking works with OD on or off.