Tow/Haul mode

[lp5151]

question about when to use the tow/haul mode in my 2007 D/A 6.6. 6 spd allison. some say anytime you haul RV trailer/load others say only in the mountains??? anyone have any experience if tow/haul mode decreases MPG vs non tow/haul mode while towing trailer/load?:confused:

[Willcoc]

My 2 cents worth...I think my owners manual stated 80% or greater of the Gross towing, should use it (or something like that). After experinance, I use it as the load dictates. The larger the load, the more likely to use it. Use is more for the grade braking then on the speed up side. Really moves the shift points high so would use more fuel at that time.

[chipper]

My 2 cents worth...I think my owners manual stated 80% or greater of the Gross towing, should use it (or something like that). After experinance, I use it as the load dictates. The larger the load, the more likely to use it. Use is more for the grade braking then on the speed up side. Really moves the shift points high so would use more fuel at that time.

X2 , based on 50K towing

[tanker]

You will use more fuel in tow/haul because you are getting a longer run in each gear, so rpms are higher than a normal run, however you are locked up which prevents slippage, thus reducing heat and putting all power through to the drive train. I have the 05 w 5spd. Allison, and it won't shift into 5th until about 55 mph in tow/haul. Pulls great. Wouldn't have it any other way.

[50+]

Can anyone answer this. I just traded my LLY 5 spd in on a 6 spd LMM. I havent pulled my trailer yet. When in drive and tow/haul is selected will the allison shift into 6th gear or is it locked out. A salesman told my brother overdrive is locked out. I didint see this in the owners manual.

[50+]

I think I have answered my own question. Got the manual out again. As far as I can see tow/haul does not lock out 6th gear. If you select manual you can lock out any gear above the gear your in, when selected. So if you selected M while in 5th gear the only way to get into 6th would be a manual upshift. Going back down in the gear range would be automatic, except for 6th? Guess I'll know when I test drive in manual mode.

[JohnC]

AFAIKT, 6-M works the same as D

[Chris_S]

My LBZ has the 6 speed, and when I tow my 5th wheel I use the Tow/haul mode. It will shift into 6th once you are up to speed.

[50+]

Chris....Thats what I'm curious about. My gn trailer fully loaded will weigh between 11,000 and 12,000 lbs. I make 2-3 trips hauling horses to Wyoming and Colorado every year. My LLY stock would pull some pretty good grades and maintain 5th gear. I'm curious to see how the LMM does in 6th. I've only got about 850 miles on so far and havent leaned on it too hard, but what little I have I can tell the LMM is considerably stronger. I leave for Wyoming the 4th of April with 4 horses, so I'll find out.

[DmaxMaverick]

Keep this in mind......

5th gear is 5th gear in all the Allison 1000 trannies. They are all the same gear ratio. The addition of 6th gear is a double overdrive. If you are towing a lot of weight, 6th gear is probably not practical for all but the flattest, least-windy stretch of road at faster highway speeds. The Duramax, of all flavors, develops good torque pretty low, but that doesn't mean you should be running it at the lower end of the torque range all the time, or under extreme loads. If the tranny isn't upshifting, it probably is an indication it shouldn't. I'm not saying you should blindly trust the computer, but running too high a gear isn't good for the engine or tranny.

[50+]

Dmax.....Thanks for advice. I have realized that 5th gear in the 6 spd is the same as it was in my LLY 5 spd, based on rpm's. I will be heavy on this trip so I anticipate using Manual mode and locking out 6th gear. My truck is still pretty new, just turned 1000 miles yesterday.

[jharden1]

FWIW there is a break in on the rear end, too, for towing. If I recall 500 miles no faster than 55 or 60. My experience is put it in drive select tow haul and let it shift when it wants, the shift logic on the Allison is pretty good.

[Rollingon]

My experience, based on 60k of towing a 15,000 5th wheel, much of it in the mountains of the West. I'm definitely not a technical expert.

T/H is worthwhile except for the "5th gear hangup", where it won't shift into 5th gear until above 55 mph, even at low throttle position. I tow a lot on rural roads at 50-55, and the hangup is a real PITA. I wind up usually towing in Normal except for slow speeds, stop and go traffic, and going down a steep grade in a low gear. That's when the benefit of better torque coverter lockup is worthwhile.

Maybe the 6 speed doesn't have this problem.

[carco]

A lot less torque converter slippage when using T/H mode thus less heat build up in trans and longer life. I have seen quite high slip percentages indicated on the Edge box in normal mode. Fuel mileage is not affected much due to less slippage in T/H mode, better fuel economy, to offset the higher shift points, assuming you reach 5th in a reasonable time. Heavier loads should generally use T/H mode. bob..................