NumberCruncher

I recently returned from a two week road trip to Colorado pulling a 2,000 pound 6x12 enclosed cargo trailer. I used tow/haul mode a little bit and noticed something I can't quite put my finger on.

When pulling up hill, the rpm's would jump a couple hundred revs but the transmission gear indicator didn't indicate a down shift. Would this be the torque converter unlocking? If so, why would that affect the rpm? I assume it was okay to drive it like this but I typically went out of tow/haul mode and just used select shift to drop the tranny down a gear so I knew what was going on.

The truck needed about 80% throttle in third gear to maintain 50 mph going up an 8,000 foot pass. I imagine a 5,000 pound load would require 2nd gear and 45 mph. This with the 5.0. Maybe this is normal and I know at 8,000 feet you are losing 25% but I was surprised by this.

NC

mbopp

The RPM increase is because the torque converter is unlocking and you're not direct coupled 1:1 anymore, now there is some slip involved.
Tow / haul raises the shift points. Did the TC unlock when you were out of tow / haul? How steep was the grade?

NumberCruncher

As soon as I went out of tow/haul mode the torque converted locked up again. I thought the torque converter was like a clutch as opposed to a gear. Why would unlocking cause the revs to climb?

This was a pretty steep grade our of Durango Colorado towards Telluride. I am sure portions were at least 6% and it was also at 8,000 feet so it was no small requirement. My only real concern is that I only had a 2,000 pound load and that was a cargo trailer no wider than the truck and only about a foot taller. I couldn't imagine what would have happened with a 5,000 pound load.

NC

MPETE

iTrader: (1)

a LOCK-UP converter functions as both. when unlocked, it is essentially a clutch allowing slip between the engine and trans, but when it "locks up" the RPM's will drop just like it engaged another gear.
its just another piece to the better mpg puzzle. what you experienced was normal.

sgtpatiolantern

Mine does the same. It feels funny, but all is good. These newer six speed transmissions don't have exactly the same feel as the old school three and four speeds. Sometimes they have a largely different feel by how they are taking advantage of the power band and changes in road conditions. It freaked me out at first, but it gets familiar quick!

tomb1269

I thought the torque converter was like a clutch as opposed to a gear.
-Yes and no. The torque convert works based on fluid dynamics. Think of it like 2 paddle wheels in the water. The engine turns one vane or paddle wheel which causes the fulid to move. As the fluid moves by (thru) the other vane or paddle wheel it cause the paddle wheel to move and thus you turn the turn the drive shaft (or eventually as there are many more places for that fulid to flow and parts to move). Now as you can assume the fluid does not cause the 2nd paddle wheel to move at the same speed and therefore you notice higher RPM. The lockup does just that locks the engine side vain to the drive shaft side vane resulting the vanes or paddle wheels moving at the exact same rate.
Hope this help you understand your tranny a little better. And I would agree with the proceedure you used. Whenever pulling a long grade under heavy load (1 ton + 8000ft (i.e. 1.5 miles above sea level) = Heavy load for a truck programed to run at an evelation closer to sea level) I would select a gear and let the truck do it job. When the tranny starts hunting for a gear is when trans fluid starts to get really hot. Just make sure your giving the engine plent of power. I would expect to have it turning around 3500rpms + or - a couple hundred, maybe more if the new 5.0 Coyote is a high rev engine.