# tow / haul on chevy hd



## S-10 Plower (Nov 28, 2003)

Is the tow / haul button on the end of the shifter like OD or is that just when you tow a trailer or haul a heavy load? My buddy said it is the OD and i should drive with it on all the time for better gas mileage but i think he is nuts and don't want to wreck the trans. 

thanks for any input.

Mark


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## ksland (Nov 27, 2002)

It is not the overdrive..... It changes the shifting habits of the transmission. Those trannys are completely computer controlled which allows this to be switched easily.


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## TLS (Jan 31, 2000)

Driving with it ON all the time will KILL your mileage.

But plowing with it on is a real good idea. It basically holds shifts longer.....This way you won't be shifting into 2nd too soon (or at all). The less shifting the less wear and tear. 

Also keep it on while transporting between jobs. Keeps the revs up to recharge your battery and keeps the tranny cooler. Prevents OD unless your going 55mph plus. Lots of benefits for plowing. Keep it ON when the plow is ON and unless your towing, keep it off when it's off.


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## BigRedBarn (Jan 4, 2003)

The Allison 5-speed automatic transmission, as far as I understand it, has both the "tow/haul" mode and overdrive disable; while the regular automatic tranny has only the "tow/haul" mode.

The "tow/haul" mode (pushing the button on the end of the stalk quickly) raises the gear-change shift points (i.e., the tranny holds the gears longer for higher revs to prevent bogging down the engine when you've got a load). The tow/haul mode indicator is a little trailer to the right of the right blinker indicator on the instrument panel.

The Allison's overdrive disable (pushing the button on the end of the stalk and holding it for a second) disables 5th gear. I guess they did it this way because otherwise they'd have to change the gear shifter (as well as the "prendle" indicator on the instrument panel) to add notch for 4th gear. When you engage "3" on the Allison you disable both overdrive gears (4th and 5th). The OD disable indicator is a "D" with a square around it and a slash through it, I think, and is to the left of the tow/haul mode indicator on the instrument panel.

On the Allison, if you push the button both quickly and then again holding it for a second you get both modes (and both indicators light up).

With the Allison, on the stalk, I guess they use a small arrow to indicate a quick push of the button and the bigger arrow to indicate pushing the button and holding it for a second. To me (and I admit I'm a bit slow on the draw sometimes if you know what I mean) those arrows aren't all that obvious. It was only after trying it for several hours that I managed to figured those two arrows out (OK, not really, I'm just joking, it only took me 25-30 minutes [OK, I'm joking again]).

Yeah, I noticed that it's good to use the tow/haul mode while plowing as you can get the Allsion to engage 2nd gear while plowing pretty often which you probably want to avoid.

If you're drag racing (which is only for the race track and not ever for use for street racing because street racing is a no-no as my lawyer advises me to say) you can give the button on the end of the stalk a quick tap to get more revs out of the engine. Not that you'd ever race a HD truck, what with having a big block, 5-speed automatic, 4:10 gears, locking rear diff and 4-wheel drive (which means that you'd get the tires to lock up much better and not just sit there with your rear tires spinning going nowhere fast) you'd probably only blow the doors off of, oh say maybe, 9 out of 10 ricers, right? Heh, heh, heh... I love ricers with no doors... am I right or am I right?


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## TLS (Jan 31, 2000)

My guess was that he had a 6.0 4L80E.

But thanks for the article.


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## BigRedBarn (Jan 4, 2003)

TLS said:


> But thanks for the article.


OK, so I'm a bit wordy... verbose, even. I guess I make up for that by being quiet in person (usually, but not always).


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## steveair (Feb 24, 2000)

I have a 6.O with the 4l80e and find the tow/haul mode to be more of nuisance than angthing else. What I don't like about it is it tends to rev the engine out and then slams the trans into the next gear abruptly. I feel that 'slam' is more destructive to the the trans than shifting more often, but maybe I'm wrong.

The worst is tow haul mode in traffic. When going at slower speeds, it runs the motor at a high rpm, then slams it into second just when traffic comes to another stop. 

I've found that in 'regular' mode, you can pretty much control the trans just by how much gas you give or don't give. You can kind of keep the transmission in the gear you want without tow haul on. 

When pulling a heavy load, I've always been much happier just putting the the gear selector out of overdrive and not using the tow mode.


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## TLS (Jan 31, 2000)

Steve,

I agree with you on the rpm part. They could lower the T/H shift points slightly, or make them adapt to slow speeds better. I haven't "towed heavy" yet....just my 5K lb landscape trailer. If you tow 10K, T/H is probably needed with the high strung 6.0. 

Unlike you, I wish the trans shifted firmer both in T/H and normal. I like snappy shifts. Slow soft ones kill the bands, and shorten it's life.


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## lawnmedic (Jan 9, 2004)

The reason for the higher RPMs in T/H is keeping the trans coll and allowing for engine braking(which greatly increases brake life). I put over 10,000 miles a year pulling a 5th wheel weighing almost 10,000 lbs. and I have never found a reason to lock out overdrive. Truck now has 95,000 miles with nothing but oil changes and tires.


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