When to tow in All wheel drive or 2 wheel drive?

[Bill]

Chevy/GMC vehicles actually have a Tow Mode button, and I would love to have some technical detail on exactly what it does. I believe - and I have no substantial backup for this - that the Tow Mode does a couple things. First, it changes the shift point RPM, much like you are doing manually on your Toyota, Rickst29. Second, I think (I hope!) that it causes the torque converter to lock up more of the time, spending less time in the partially-locked states that are normally used. The partially-locked states give a more comfortable ride because they simulate a whole range of partial gears between (for example) 3rd and 4th, or between 4th and 5th. But partially-locked is also a heat generator, and becomes a real problem with the extra load of towing a trailer.

Ford (mine, for instance) and other vehicles have an Overdrive Lockout button, which simply tells the tranny not to use the upper gear or gears. But as near as I can tell, behavior in the lower gears is unchanged. I don't believe that this is the same as the Chevy Tow Mode.

If anyone has access to a comprehensive description of what Chevy's Tow Mode really does, I would love to see it.

Bill

Bill,

Ford also has a "Tow/Haul" mode rather than an OD Lockout on some models (at least the current superduty trucks). Looking at my truck's service manual, it does the following:

- Uses all gears (including O/D)
- Changes the shift points so that they occur at a higher speed for a given accelerator pedal position
- Torque converter will lock up at lower speeds with a given accelerator pedal position
- Upshifts are temporarily delayed while decreasing accelerator pedal position during hill cresting to reduce excessive transmission shifting and to prepare for engine braking
- "Engine braking is provided in all forward gears without the requirement of moving the selector level"
- Manual "1", "2", and "3" selection is still available
- Grade braking downshifts happen when "positive vehicle acceleration is sensed", a "near zero" accelerator pedal position is obtained, and a minimum amount of time has expired since the last grade braking downshift". It's deactivated when you press the accelerator more than the threshold.

If I remember my Chevy right, it was similar. It turned on engine braking, made the torque converter lock up sooner, and changed the shift points. It also caused you to get 5 (or was it 7?) turn signal "winks" instead of 3 "winks" when you just quickly tapped the turn single indicator and increased the voltage of the charging system (presumably to better charge a trailer battery). It also used a different "learning memory" in the transmission than the normal mode (the transmission apparently learns when to shift over time - and that information is obviously different when towing than not). That was on a 2007.5 2500HD diesel. O/D was still used in tow haul mode.

Think I've got the same engine/tranny as Rickst29. It's a new vehicle to me and on our recent trip from Texas to Ontario I was paying more attention to the trailer than the truck.

It wasn't until about halfway back that I realized that the downshift on slight grades was not to 4th but really the torque converter unlocking. So up to then we spent a lot time with an unlocked torque converter. But it was cold and the truck does have a tranny cooler, so hopefully no permanent damage was done. A tranny flush is due at the next service too, so that may help.

My only problem with 4th is the increased noise. I think they tune these things to sound tough when accelerating.

[Bill]

Grakin -

That's EXACTLY what I wanted to know! Many thanks for posting it. I wish my Explorer had a Tow/Haul, instead of an O/D Lockout. Other than that, it is a great tow vehicle.

Bill

[rickst29]

Originally Posted by brulaz

Think I've got the same engine/tranny as Rickst29. It's a new vehicle to me....It wasn't until about halfway back that I realized that the downshift on slight grades was not to 4th but really the torque converter unlocking. So up to then we spent a lot time with an unlocked torque converter.

I'll use the word "clutch" instead of the words "torque converter" in this post. I forgot to say that the cause for bad gas mileage (and the excessive wear-and-tear on the tranny clutch and fluid too) is running "unlocked" for extended periods.

You should downshift to a gear where you can raise your foot up, just a bit, to see the 100-150 RPM dropoff which occurs when the clutch locks up -- and also maintains that locked state as you push your gas back in, slowly, to accelerate back to the speed you want to go.
- - - - - -

Here's my original, and better written, instructions: Driving Toyota/Lexus SUV Automatic Transmissions

I've owned both the V8 and V6 models of "Gen4" 4Runners. The V6 was bought with insurance money as a slightly-downgraded replacement for the V8. (RIP. Here's the sad story: Totaled from behind by a driver who died at the wheel and slumped forward - onto the gas pedal. 9000 lb van conversion smashed into us from the rear, while we waiting at a light, at nearly 60 MPH. Two vehicles in front of us were also totaled within the resulting "accordion". Wife said, "You buy another one just like it!!", but the only "Sport" model in stock was a V6.)

The V6 is much more noisy than the V8 was, but we find it capable of handling grades up to 20% easily... and our 2619 is loaded heavy for travel, at least 200 lbs past the official GWV rating. (That's why we got it with the 3124's axle and tires.) Having years of experience with both, I strongly recommend the V6 model-- better mileage, no significant loss of capability if you drive it with high RPMs when necessary. Shift it like a manual, and the only difference is more noise. You put the right one in your Taco.

Thanks Rick that's a good write-up.

What's funny is that the cruise control was doing a lot better at managing the tranny than I was. It would drop very quickly through the unlocked torque converter down into 4th.

I was trying not to use cruise, thinking I could save some gas, yadda-yadda. Ah well. You live and learn.

And yes, the Taco V6 works just fine with the Elkmont too.