Auto Trans Gears/Overdrive

Ok, I have a 2009 LB Sport 4.0 Auto trans. This is a five speed transmission correct? I can select 1-2-3-4-or D (4 gears and 1 overdrive?) When I am cruising at freeway speed, say 70mph. I will be at about 2100rpm. Occasionally when pulling a hill into the wind the truck will do a small down shift and my rpm's will go up to 2500 or so. Now at the same speed if I grab my shifter and move it into the "4" position my rpm's will surge up to about 3000rpm's. Is the small down shift the trans coming out of overdrive? but that would suggest it was a five speed plus overdrive. Am I making any sense? I wish there was a way to force the small down shift for towing, like and overdrive lockout, if that is the case?

 

Sounds like the small downshift, may just be the torque convertor unlocking. Drive 70 and just tap the brake, you should see the same rpm jump

That or downshifting it manually unlocks it with the downshift and not auto

Id say the answer is one of the above, probably the first judging by the change

you have 5 gears total. D is 5th gear, and is an overdrive (ratio < 1)

4th gear i believe is 1:1

If you want an overdrive lockout, drive in 4th. Same thing

 

I thought of the torque converter but it would not make sense to unlock under load, you would create a ton of heat?

 

It does not make a tremendous amount of heat. Unlocking the torque converter provides a small amount of torque multiplication, so it is similar to dropping a gear.

I seem to recall reading that this transmission can do TC unlock in two stages, but I am not entirely sure what that means.

 

Old thread, but dw77x describes exactly what I've seen towing a 3500# trailer back from Texas. On the straight, the auto stays in 5th. On a small grade the rpm's go higher, but not as high as when I force it into 4th gear. So if this intermediate 4.5 gear is really the torque convertor unlocked, should I allow it when hauling the trailer or force it down to 4th? There were a lot of grades between Texas and Ontario and some were long and steady. I've got the tow package with tranny cooler but everything I've heard about unlocked torque convertors is that they generate heat, and you don't want to leave them unlocked for long. ??

 

I've had the same question in mind for some time about my 06. Try this. On a level smooth road drive with shifter in 4th and tach at say steady 2000 rpm (around 60km per hr). Keep the gas pedal steady. Now while watching the tach, drop the shifter into D. There will be an rpm drop to around 1600 rpm, then shortly the tach will fall to about 1100-1200 rpm. This pattern shows up at different cruise speeds though the relative rpm proportions seem to change a little.
I prefer to keep my shifter in 4th while city driving (under 70km per hr), and when towing heavy loads. Otherwise in D this "shifting" behavior has the trans hunting back and forth between the 5th speed and, from what I can guess from other posts, the torque lock mode. Also, in town if I leave it in D and need a quick acceleration if its in 4th the tranny response is alot faster and smoother than gearing up from D.

 

hokay. 4th gear it is on long grades.
I didn't realize that it was not 4th gear until the trip was almost over.
Tranny should be ok, hopefully, as temperatures were cold most of the way.

 

Yup, the torque converter unlocks when upshifting as well to smooth out the transition. It's what it's supposed to do I guess.

I've also heard that gas mileage isn't affected that much when you run at higher RPM's in 4th, versus lugging it a bit (throttle further to the floor) in 4.5th (with the torque converter unlocked).

So my only real problem with 4th is the increased noise.