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Old 01-19-2011, 10:08 PM   #57
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Originally Posted by tinearpaul View Post
Not sure I understand why they make 3/4 ton trucks if the cost difference is so.
Tax and tags in some states once 10,000 GVWR is exceeded skyrocket, some insurance consider commercial (as does some states for scales).

Two of my three states (Maryland and California) are such states as is I believe Mass.

Some companies (such as Ford) allow an option to get a sticker degrading the vehicle to 10,000 lbs GVWR so non commercial folks are not affected by said laws and/or limitations set by GVWR sticker.

Thus I ordered my F-350 with said option - standard F-350 truck but with optioned tag and title of F-250....

That's the gist of it, do a search if you want my full explanation...
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Old 01-19-2011, 10:12 PM   #58
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Looked at Denali GMC 1ton SRW - for me King Ranch was easy choice...
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Old 01-19-2011, 10:13 PM   #59
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Originally Posted by webtrippin View Post
Neighbor at the park we're at now and I were talking yesterday, he has an 03 and I have an 04 Duramax. He said he's had the tranny replaced, blew a gear in the middle of an intersection when he wasn't towing. Said he thinks it was due to not using the tow/haul mode when he was towing before that, and now he uses it all the time.

Dunno if thats common or what, but I read in the manual previously that it should be used when towing heavy but no suggestions on what heavy actually means. He's got something that looks like an upper 20 foot TT, you know one of those box shaped ones.

I have also heard some other people having issues with the control module or valve body but not with the tranny itself.
Recommendation is that tow/haul mode be used when Trailer weight is 75% of max trailering weight or more. Doesn't hurt to use it if you are lower that the 75% figure, but it will use slightly more fuel unnecessarily.
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Old 01-19-2011, 10:22 PM   #60
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From the 2011 owners manual. Other years have similar wording.



Pressing this button at the end of the shift lever turns on and off the Tow/Haul Mode.




This indicator light on the instrument panel cluster comes on when the Tow/Haul Mode is on.
Tow/Haul is a feature that assists when pulling a heavy trailer or a large or heavy load. See Tow/Haul Mode for more information.
Tow/Haul is designed to be most effective when the vehicle and trailer combined weight is at least 75 percent of the vehicle's Gross Combined Weight Rating (GCWR). See "Weight of the Trailer" under Trailer Towing. Tow/Haul is most useful under the following driving conditions:
• When pulling a heavy trailer or a large or heavy load through rolling terrain.
• When pulling a heavy trailer or a large or heavy load in stop-and-go traffic.
• When pulling a heavy trailer or a large or heavy load in busy parking lots where improved low speed control of the vehicle is desired.
Operating the vehicle in Tow/Haul when lightly loaded or with no trailer at all will not cause damage. However, there is no benefit to the selection of Tow/Haul when the vehicle is unloaded. Such a selection when unloaded may result in unpleasant engine and transmission driving characteristics and reduced fuel economy. Tow/Haul is recommended only when pulling a heavy trailer or a large or heavy load.
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Old 01-20-2011, 06:31 AM   #61
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Watch your transmission temperature and you will be convinced to always use the Tow/Haul Mode when towing an Airstream, even on rolling interstates.
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Old 01-20-2011, 08:11 AM   #62
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Quote:
Originally Posted by webtrippin View Post
Neighbor at the park we're at now and I were talking yesterday, he has an 03 and I have an 04 Duramax. He said he's had the tranny replaced, blew a gear in the middle of an intersection when he wasn't towing. Said he thinks it was due to not using the tow/haul mode when he was towing before that, and now he uses it all the time.

Dunno if thats common or what, but I read in the manual previously that it should be used when towing heavy but no suggestions on what heavy actually means. He's got something that looks like an upper 20 foot TT, you know one of those box shaped ones.

I have also heard some other people having issues with the control module or valve body but not with the tranny itself.


Do you have any knowledge of how many miles he had at this point?
Like any mechanical component; there will be failures, but as noted I do not know of any (outside of this…which I guess we can consider factual?) of an Allison.
It would be great to know some of the deets…

I do know that we have had 3 trucks with tow/haul. They put it there for a reason. However; failure to use it, should not result in a blown tranny!

Bill

(p.s. I thought this was a Duramax/Alli thread?)
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Old 01-20-2011, 08:58 AM   #63
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I forget the exact mileage but I remember it being low. Maybe 60k miles or something. He's from Canada so was talking in kliks and I was doing the conversion in my head at the same time. Trailer weighs about 7k lbs.

I have never seen my trans temp move much at all. Loaded or unloaded my rule of thumb for watching it is ambient plus 100. The exception to this is towing up a steep constant grade in overdrive (bad idea don't do it) and I always kick the o/d off. I won't be able to hold speed if I don't anyway. Maybe someone with a programmer has a different experience but I am mostly stock.
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Old 01-20-2011, 09:12 AM   #64
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Allison temperature

My transmission temperature seldom varies. I never see it move except on a long climb in hot weather. Then it moves very little.

I normally run without tow haul and with the gear selector in manual. The truck stays in 6th gear almost constantly. As I approach a hill and feel the engine start to work, I hit the button to shift down to 5th, well before the Allison would shift down. That gets me over all but the steepest hills. Once on the upgrade, I hit the button to shift back up and let the truck decide when to shift back into 6th. This gets me the best fuel mileage and I never get a rough or double downshift.

I do turn tow-haul on when towing in the short ups and downs of the Texas Hill Country. At the speeds I tow (62), the truck stays pretty constantly in 5th with T/H on.
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Old 01-20-2011, 09:25 AM   #65
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Originally Posted by Pahaska View Post
I do turn tow-haul on when towing in the short ups and downs of the Texas Hill Country. At the speeds I tow (62), the truck stays pretty constantly in 5th with T/H on.
John,

That's my experience also. And I've noticed if I don't get it fast enough to get into 6th gear (about 64) my fuel mileage suffers.

It will go into 6th at lower speeds if not in T/H, but I figure GM put that feature on there specifically to save the transmission and allow the truck to "handle" the load easier, as in going down grades and slowing down, so I use it.
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Old 01-20-2011, 01:24 PM   #66
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We tow at 63 mpg for peak efficiency.
Try this; accelerate to about 65-67 in TH mode, when you see/feel the RPM drop down, lock your cruise control. Then tap the decelerate button until you hit 62-63mph. The revs will stay at ~1700 without downshifting and you will get the best fuel efficiency. You might call this “over compensating”…you have to go beyond the shift point
(~65-67 mph for the 6 spd Alli) and then back off (without going too far). Diesel engines achieve peak efficiency on either side of peak power (1800 RPM) so 1700 RPM should be ideal for efficiency and very near peak power. We were getting ~15 mpg towing like this, this past season we are getting ~16 mpg (the truck is approaching 50k miles and is used only as a TV/HV or for extended ski trips, not much around town). Efficiency seems to have improved a bit again this past year.
I think the next shift point down, and even more efficient is ~59 mph, I have been able to get ~ 20 mpg towing at this speed, but I find this too slow.

I have found no difference in fuel consumption towing at steady state speed in TH, not in TH, or in “M”.
But I do like having the engine braking feature which is only available in TH.
There is a significant difference in stopping with TH on. Kind of like throwing an anchor off the stern…
Play around with these features next time you are out. It is a wonderfully flexible power train. After 5 seasons, I am still amazed by its capabilities.

Notes;

o This is based on towing at 63 mph and achieving peak efficiency. If fuel mileage does not matter to you…then go for broke! But TH does make a significant difference in stopping. At any speed. It is a great feature in bumper2bumper traffic.

o I do not believe any of this applies to the 5 spd Alli which would have different shift points ( IIRC also does not have engine braking?).

Bill
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Old 01-20-2011, 01:47 PM   #67
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5 speed does have engine braking in tow haul mode. I use that all the time. Sometimes its a little slow to release though which is annoying.

I have been thinking about the diablo programmer because it has a tow performance and economy mode that supposedly adjusts power some but also shift points. Also has diagnosis and adjusting speedo for tire sizes too. Anyone have experience with that one?
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Old 01-20-2011, 07:53 PM   #68
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Does the engine also have a exhaust brake or is that just with the newer models ala the turbo?

Asking for a friend....
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Old 01-20-2011, 10:25 PM   #69
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Does the engine also have a exhaust brake or is that just with the newer models ala the turbo?
No there's no jake brake standard, just the trans programming that downshifts when you're on the brake going down grades or drop below a certain RPM.
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Old 01-20-2011, 11:39 PM   #70
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The 2011 Duramax powered GM pickups DO have an exhaust brake (via the turbo), which coupled with the Allison, gives truly amazing downhill (mountain) speed control. There are several after market programmers that can add this feature to older Duramax powered pickups.
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