Need a little info on towing?

[Big_Daddy_T]

When do these trucks downshift. Say I had about a 10000 pound load would it shift into third if I hit a small to medium sized hill? Could I tow at 65-70 with a chip up a 4-6% without being glued to the egt gauge?

 

[Steve M]

My bone stock SO 47RE/4. 10 will hold O/D with cruise on from 70mph down to about 55mph before it downshifts while towing 10,400 lbs. A 4-6% grade is going to call for a shift to third so I lock out O/D before I even get there. The HO/48RE will be alot stronger and hold on for alot longer but I assume the scenario would be the same with the downshift. If you're running stock power, you don't need to stare at the gauges. I give a quick glance now and then. With the VDO gauges, less than straight up on the needle is safe.

 

[sdbelt]

I pull 12k lbs with my 48RE & HO. Before a lengthy hill of 4-6%, I will hit the OD off button, as the stock motor won't pull a steep hill for very long, and the shift happens too late to maintain good momentum. I can pull a 4% hill at 65+ mph, and a 6% hill at 60 mph (usually).



When pulling in OD, I like to cruise in the 70-75 mph range, because momentum, combined with the engines power sweet spot, make this a very comfortable speed range (I have 3. 73 gears). For shorter hills, or rolling hills, this speed range means no auto shifting for the 48RE.



For longer hills or rolling hills at a lower speed, then I go OD off.

 

[DBVZ]

I think the 48re is programmed to hold in OD longer than it should before a downshift to 3rd. When climbing in OD at 15-1700 rpm, if you hit OD off you get into a better power and torque range and the truck just feels better pulling hard when it is turning over 2000 rpm. If you immediately hit OD on, the transmission will stay in 3rd until you top the hill. Max power and torque are at about 2600, and it drops off rapidly above that; so if you want to maintin 75 or 80 pulling uphill, a downshift to 3rd is probably not good. It seems to me it knows the right time to shift up to OD, but is slow to shift down to 3rd. I guess if you have a short grade to climb, staying in OD works fine if you stay above 1500 rpm. If it lugs down below 1500, or you have a long grade in front of you, shifting down to 3rd just takes pushing the button. If you push it a second time, after the downshift, you can just let it shift up on its own. My $0. 02.