Tow Haul Mode

[Very Old Dog]

According to the owners manual, it says that you should use "tow haul mode" when the combined load is 75% of the Gross Combined Weight. The Max gross combined weight of a Duramax/Allison short bed extended cab 4x4 is 22,000lbs. When do you use the tow haul mode? And what do you figure/estimate your weight to be percentage wise.

The reason I am asking is that I am about to hook up a Trail-Lite TT RV 23ft vehicle and fully loaded it will weigh 5600lbs ( dry = 3500lbs) but I doubt that it will be carrying that much for weekends. Should I use tow haul mode or can I drive the vehicle under normal circumstances and just put it in "D" with normal overdrive? Thanks for your input.

[BigBob]

from my experience, my trialers in the 7000# range and I seldom use the tow haul mode except on fairly tall grades, or when slowing down to let the engine slow the truck and trailer as the transmisson down shifts,

in tow haul there are a few advantages 1/ once in 2nd gear the transmission goes into complete lockup(vs 5th ) , 2/ the shift points are higher for a more aggressive take off 3/ when braking the the progressive down shifting of the transmisson

the allison is a true five speed , it is not like cummins were the tow mode locks out 4th or overdrive while towing( reducing your top speed capabilities) , because of the complete lockup once in 2nd the torque converter is not slipping and adding any unnessary heat to the transmisson oil.

[Maverick]

Towing that much I would use the T/H. Besides the benefit of downshifting on grades, your tranny will run cooler in stop and go traffic and in the mountains as Big Bob said.

[Nixter]

Just try it out and decide for yourself. I rarely use mine with light trailers except for during city driving or mountainous terrain. I have never used OD lockout but I can see where it would be useful. With my last truck these features would have been more useful to me. My D/A has enough power that it doesn't need them for most of my applications. --Nick ;)

[DieselDixon]

I like the T/H mode for the down shifting. I find that I use the breaks less because of this and there have been a couple of times I had to break hard and the tranny down shifted quickly which helped slow me down as well.

[mike.morris]

I pull an 18' Ranger bass boat, and I have pulled with and without tow/haul mode engaged. Interstate driving made little difference in tranny temps, but in town, I found the tranny fluid temp would be 10 to 20 degrees warmer when not in t/h mode. I agree with the others that the engine breaking / downshifting is a great advantage especially when breaking hard. Hope this helps.

[NWDmax]

What Mike said!
Experienced the same thing pulling my 18 foot Nitro bass boat.

[Lone Eagle]

Very Old Dog, Maybe this will help.

Regular Mode

The converter is unlocked in 1st,2nd,3rd & locked in 4th & 5th.

Tow/Haul/Race

The converter is unlocked in 1st, locked or unlocked in 2nd & locked in 3rd, 4th & 5th.

Later! Lone Eagle ;)

[Oongawah]

I always carry my DMAX cocked, locked & loaded. Or is that my Star 9mm Model BM? :D :D :D

I do wish I had OD lock out for those rare occasions when EGT's are high. In T/H mode it does stay in the lower gear better when pulling hills. It's just one of those Tranny/Driver learning things. Have fun, Chuck.

[Norm B]

Hope this does not get posted twice. I lost it just as I was ready to post.

Re: Tow Haul and EGT. On my recent trip pulling my 27ft 5th wheel from Salt Lake to Reno on I80 I saw the engine temperature go above the thermostat hold point for the first time(26K miles). Twice in fact on the long grades near the Utah/Nevada border. Outside temperature was in the 90s. I ran the hills in cruise control at 3000 to 3200 rpm with out being in T/H. Do you think I was running dangerously high EGT? I kinda resolved to myself not to do this again but have not had the same kind of conditions to try it out of cruise at lower rpm.

I agree with the posts above and alway use T/H on long slow speed grades(loaded or unloaded) and find the transmission temp will run 10 to 15 degrees lower. The transmission temp was not an issue on the trip mentioned above.

[DieselDixon]

Originally posted by Norm B:
Hope this does not get posted twice. I lost it just as I was ready to post.

Re: Tow Haul and EGT. On my recent trip pulling my 27ft 5th wheel from Salt Lake to Reno on I80 I saw the engine temperature go above the thermostat hold point for the first time(26K miles). Twice in fact on the long grades near the Utah/Nevada border. Outside temperature was in the 90s. I ran the hills in cruise control at 3000 to 3200 rpm with out being in T/H. Do you think I was running dangerously high EGT? I kinda resolved to myself not to do this again but have not had the same kind of conditions to try it out of cruise at lower rpm.

I agree with the posts above and alway use T/H on long slow speed grades(loaded or unloaded) and find the transmission temp will run 10 to 15 degrees lower. The transmission temp was not an issue on the trip mentioned above. If you are totally stock there is no way you did anything wrong and your EGT's were fine. My 03 is totally stock and I put a EGT gauge on it before I went on my first trip (pre-turbo). I never saw the EGT's go over 1200, one time it hit 1200 and that was only for a second or two. I think having a stock truck the computer will never let this happen.

[Lone Eagle]

Oongawah, If you are going to drive the biggest, baddest diesel pickup you need to trash that 9mm and buy a Gov. Model .45 ACP. Later! Lone Eagle :D

[NewEnglandDmax]

Let me ask you all this, I am taking a trip up the 6000 ft Mount Washington in NH. On the way down, I plan to put it in 2nd or 3rd. I like the TH mode for the downshifting. I can still use the TH mode when I put the Allison in 2nd or 3rd, right? Also, Gotta go with the Smith and Wesson 10mm or a nice 44 mag. revolver.

[Very Old Dog]

Well folks, I brought home my new trailer and I used the Tow/Haul Mode. When I pushed the button it first went into Overdrive Off. Pushed it again and it went into Tow/Haul OD off and pushed it a third time and it was just Tow/Haul mode in "D" and that is where I wanted it. I drove along with smooth shifting and great acceleration. It really did not notice the 3500 lbs Trail-Lite 23ft trailer behind it. As a matter of fact it hardly moved when the weight of the trailer went on the hitch ball. You really do notice the extended acceleration before shifting, somewhere between 2500 to 3500 RPMs but that is ok. No increase in temperatures and shifts to fifth gear over 50 to 55mph. Runs very smooth and the prodigy brake controller works great. For those that are interested in the other towing attributes, I am using a Reese Trunion hitch for weight distribution and Reese High Performance dual cam sway control. Excellent. I cruised on I40 East of Knoxville at 65 very comfortably had it over 70 and it was extremely stable. I feel better at 65 myself and that probably will be my cruising speed. Filled up the diesel and I add Stanadyne Performance Plus to give it a boost and keep the injectors clean. For those interested, I order the Standadyne through USDiesel who I connected with on the Internet thanks to this website which has them as an advertiser. I want to thank all of you guys for your input.

[Very Old Dog]

Just one more thing: I purchased the brake controller wiring harness from the GM Parts department from my local dealership where I purchased the vehicle. The RV dealership mechanic installed the harness and connected it to the Prodigy brake controller with an in-line fuse and used the two screw holes below the steering column to mount the contoller. When we plugged into the trailer throught the connector factory installed, all lights functioned correctly and the controller worked appropriately as earlier reported.

In the fuse box under the hood, there was a blank labeled "Stub #1". The GM Dealer called GM technical support and asked what fuse went in there. It turned out that it was a 40 amp square Maxi fuse and this location is used to pass power back to the trailer power box to charge the battery and provide auxilliary function. The location labeled "Stub #2" was already filled with a 30 amp maxi fuse because the truck came with the Trailer Towing package and pre-set for the brake controller.

Now, I would prefer the 45ACP Colt Gov't. Service Model which I carried for 23 years in the Marine Corps and for 18 months in Viet Nam through mud, dirt, sand, water, rain and crap. One thing for sure, the 45ACP would come up firing all the time. The Berretta is a great piece, but I never put it through what the 45 went through. And the M16 was a piece of sh......t then so I switched to a WWII Thompson 45ACP. Heavy but worked when your life depended on it.

[Oongawah]

OK, You all talked me into it. Do you know where I can get a Gov't Colt 45ACP? The Star is easier to carry than my ParaOrdinance P45.

As far as T/H mode, is anyone running L4 in it? My EGT's are definately higher since putting on the 285's, and the 45 Gal tank. I wouldn't push it.