tow/haul mode

[Montana_89]

In reading about the Allison 1000, it stated that by "pressing the tow/haul button once, it changes shift pattern." That I understand! But, it also stated that by holding the button in a short time, the overdrive feature is blocked! All you Allison owners... whether diesel or 8.1, is this possible and do you do it? I pull just under 15,000 lbs. and I'm not sure if I am doing it completely correct. Please give me you expertise!

[Karl]

That is the way it works, however, I don't usually lock out the overdrive. My unit is about the same weight as yours, and I am pulling with a diesel. The only times I have locked out overdrive have been times that I have been pulling into a strong headwind and don't want the transmission shifting back and forth between 4th and 5th gears.

[Flastro]

Yep, you are correct, My 03 2500HD had the exact tranny with the Duramax, a quick push of the button, tow/haul mode is in place, hold the button for a couple seconds and the overdrive locks out.

[CountryGuy]

Art,

Yes, by holding the button in for a short time, overdrive is disabled. When you want to put it back into overdrive you hold the button in for a short time again. To toggle between tow haul mode simply push the button in quickly.

I tow in tow haul mode and with overdrive disabled. So when I first start out, I push the button quickly to get to tow haul mode and the push the button again but hold it longer to get it to disable overdrive.

The Allison 1000 transmission is a 5 speed transmission with 5th gear being the overdrive gear. In tow haul mode overdrive will not engage until about 62 MPH. I find that if I travel at this speed or more, engine RPMs will be in the low 2000 area. At these RPMs, I feel there is not enough adequate torque with my setup to maintain a steady speed other than on perfectly flat terrain. The transmission wants to hunt back to 4th gear too much in order to maintain the set speed.

So this is what works for me. I use tow haul with fifth gear locked out - this means that I am towing in 4th gear all the time. I set my cruise control between 55 and 60. My RPMs range from 2500 to 2800. I have more power because of the lower gear and higher RPMs. I rarely drop down to 3rd except on the steep hills. Another benefit to locking out overdrive is that you will have better engine breaking when descending hills.

I have experimented towing both with and without overdrive. I found that I had to set my cruise control close to 70 MPH on slight hills with overdrive on to keep from dropping back to 60 and dropping back to 4th. This is faster than I like to go. At lower RPMs, the engine doesn't maintain it's peak torque. On the 8.1 gasser peak torque occurs around 3200 RPMs. When I travel at lets say 58 MPH - a speed that I feel is safe for me - my RPMs are around 2850, which is closer to peak torque curve of 3200 RPMs.

I hope this helps.

Al

[NJ Hillbilly]

The O/D lockout is there to let You disable 5th if the trans is hunting back and forth from 4th and 5th. Shifting creates a lot of wear and heat.

The lockout is on the '03 and newer trucks. When I have a hunting problem with my '02 I try shifting out of T/H to see if it helps. I also shift out to force an upshift at around 60 or so, after the upshift I engege T/H again.

John

[Montana_89]

Thanks for all of your input.

[mobrownies]

Art,
There should be a light on your dash to confirm what mode you are in. I like the tow/haul mode in town and on two-lane rolling roads - better starts and stops. On Interstate it does not make much difference except on steep grades.

[Montana_1683]

Art:

I don't use the tow/haul side of my allision tranny. Trailer Life had an article in one of their magazines, I don't remember the issue, regarding this feature. I have traveled to Chicago, Minnesota, Oklahoma City, Tennesee, and various places in Missouri & Arkansas pulling a 26ft Prowler with a superslide. I found that if I don't use the cruise control, also suggested by Trailer Life, and anticipate any hills; the tranny rarely drops out of overdrive. This is at about 2000 RPM's and doing 70 MPH.

June we bought a Montana 3295RK, have taken 2 trips in it, Melvern Lake about 65 miles from home and to Bella Vista, Arkansas about 251 miles. Likewise, using overdrive without the cruise control only on a real good climb does the tranny drop down to 3rd gear. Still at the same RPM's and does good maintaining 70 MPH in the flatlands. In the hills of NW Arkansas the speed would drop to 65 - 68 without losing overdrive. The tranny temp gauge on the dash never budges from when running solo.

When I first started pulling, our first trip to Minnesota, I used the cruise control from Kansas City to Des Moines. I noticed that when the tranny down shifted, it not only went out of overdrive but went to 2nd gear then back to 3rd gear. Wasted a lot of diesel fuel doing this; also didn't like the hard shifting.

Gary

[NJ Hillbilly]

One thing that T/H does is it immediately locks up the torque converter in 2-5, out of T/H only locks it in 4-5. The grade braking is also more active in T/H.

John

[OntMont]

quote:Originally posted by NJ Hillbilly

The lockout is on the '03 and newer trucks.

GM issued a bulletin on how to add this feature to older trucks. GM dealer should know about it, or you may be able to find it on the internet. (I have not done it, so I can't comment on how difficult it might be, but it sounded pretty simple).

[NJ Hillbilly]

I read about it on the net. One requirement is that the trans has updated software to support the lockout feature. I do have the updated software but have yet to install the switch.

John