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hriker
05-21-2012, 05:57 AM
I am still new to the RVing life and have a question about towing our rig. We have a Chevy Silverado 3500 with Duramax Diesel and Allison transmission. My question is regarding the tow haul mode for the transmission. Should we leave the truck in tow haul mode the entire time we are towing? The dealer indicated I could take it out of this mode when we get to highway speed. I have had a question in my mind about what is the proper way to utilize this and what is best for my truck. Any comments and recommendations would be welcome.

Thanks,
Harry

DMitch
05-21-2012, 06:08 AM
I have basically the same truck and I always tow with the tow haul on even at highway speeds. The Allison manual recomends it also so I figure there must be a reason they do.

PhotoPete
05-21-2012, 06:14 AM
I am still new to the RVing life and have a question about towing our rig. We have a Chevy Silverado 3500 with Duramax Diesel and Allison transmission. My question is regarding the tow haul mode for the transmission. Should we leave the truck in tow haul mode the entire time we are towing? The dealer indicated I could take it out of this mode when we get to highway speed. I have had a question in my mind about what is the proper way to utilize this and what is best for my truck. Any comments and recommendations would be welcome.

Thanks,
Harry

I believe the primary intent of the mode is to change shift patterns to accommodate the extra weight you are pulling. This would be seen most graphically in the start / stop nature of city and rural driving. It would also be seen in that zone of highway driving where the transmission wants to jump back and forth from higher to lower gear.

I have found that leaving the mode engaged for the rural and city helps smooth the work for the engine and transmission. I find that, at highway speeds with my light load i don't get the transmission jump so i disengage the mode at that point. I have noticed that i get better gas milage at highway speeds disengaged. and thats understandable as the truck runs at a lower rpm while disengaged.

I would suspect at your trailer weight you might fine it beneficial to keep it engaged more often than I need to.

Pete

hriker
05-21-2012, 06:26 AM
I have basically the same truck and I always tow with the tow haul on even at highway speeds. The Allison manual recomends it also so I figure there must be a reason they do.

I don't know that I have an Allison transmission manual. Is it available online?

danemayer
05-21-2012, 08:16 AM
Here's a couple of pages from the 2011 GMC manual. Several benefits of tow mode are listed.

I leave it in tow mode the entire time I'm towing. The only exception is if I'm at 55 mph and want to force a shift to overdrive, I'll push the button to release tow mode, and then press it again after the tranny shifts.

jayc
05-21-2012, 08:22 AM
Here are some suggestions that I found on FAQ about the Allison transmission on The Diesel Stop



Q. Tow/Haul vs. Normal Mode - What's the difference between Tow Haul and Normal Mode?



A. Tow/Haul (T/H) shift mode significantly changes the transmission's shift pattern to reduce shift cycling and to deliver better performance, control, and cooling when towing/hauling heavy loads. For instance:


Upshift points are raised at light to mid throttle position to use more of the engine's available power for accelerating.Downshift points are raised to enhance engine braking to help slow the vehicle.
During deceleration, the torque converter clutch (TCC) remains applied at closed throttle to much lower vehicle speeds to significantly improve the effect of engine braking.
During acceleration, the TCC is applied in 2nd range and remains applied in 3rd, 4th, and 5th. This improves the drivetrain efficiency and significantly lowers transmission sump temperature when towing heavy loads. In Normal mode, TCC generally applies only in higher ranges and is dependent on throttle position.




Back To Top (//heartlandowners.org/#TOP)





Q. Tow/Haul vs. Normal Mode - When should I use Tow/Haul?



A. T/H mode is recommended whenever you are towing or the truck is heavily loaded, for all the reasons noted in the above question.

Bob&Patty
05-21-2012, 10:26 AM
Yes, by all means leave the T/H engaged when towing. You can however disingage it when you reach your highway speeds. That way the trans will shift into TCC lockup. It will reduce your RPM's about 150. I do this when towing and after the RPM's drop I can then reapply the T/H button. That way I dont forget to reapply it the for the trans braking. Just the way I do it and has worked fine on the last 2 D/A trucks I have owned. Ther is also 1 other function you can use. Pull the shift lever into "M" and use the paddle shifter to lock the trans into a certain gear. All the information for the trans should in your owners manual.

hriker
05-21-2012, 11:28 AM
Thanks everyone. I had a feeling I should be using T/H mode all the time. I haven't experienced any shifting issues but the improved cooling and braking are pretty important!! I'm glad I asked. As usual everyone is very helpful!!

Hastey
05-21-2012, 12:13 PM
The only exception is if I'm at 55 mph and want to force a shift to overdrive, I'll push the button to release tow mode, and then press it again after the tranny shifts.[/QUOTE]

You know Dan, I think that is the only complaint I have about my Allison is having to do the exact thing you are talking about.

I have the edge monitor in my truck and it allows me to see what the transmission is doing. When in T/H mode it stretches out the shift points and also allows the torque converter to start locking in 2nd gear instead of 5th only. Keeps the converter from slipping while towing.

porthole
05-21-2012, 01:07 PM
Don't have the Allison anymore, but when I did I did the same as others, kept it in TH until I wanted to force the 6th gear shift.

The converter locking up early is a huge advantage.


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Duramax1
05-21-2012, 06:13 PM
I agree that forcing the transmission to shift into 6th will reduce the RPM's by 150 or so.

But reducing the RPM's does not improve the fuel mileage performance in fact, in my experience, it reduces the mileage performance.

I have a ScanGauge which is manufactured by Linear Logic. This instrument, which plugs into the trucks computer, provides many different readings on the status of the engine.

One of the gauge choices is to enable a real time fuel economy readout which I have used to validate the deterioration in mileage when shifting to 6th gear.

My experience has been that while towing on a perfectly level road at 55 mph and using cruise control in tow haul mode I will note the real time fuel economy. I will then force an upshift to 6th by disengaging the tow haul mode while continuing to use cruise control.

Immediately, the RPM's will decrease, but the real time fuel economy will decrease from what was being achieved in 5th gear.

Thus the benefit of a decrease in RPM's in this instance is being more than offset by an increase in the amount of throttle that is required to maintain the constant speed of 55 MPH in a higher gear.

Using cruise control ensures that it is a computer and not a foot movement that is changing the amount of throttle.

So in my experience, RPM's do not tell the whole story.

scottyb
08-01-2012, 10:57 AM
I can't find this using the "search", so I'll ppost it here. What is considered too high for transmission temperature, when towing with the D/A. My 2007 has a factory cooler with the towing package, but I assume it is smaller than it needs to be. I took delivery on my Cyclone yesterday and on the way home, it reached 204 at one point (ambient temp was 102). I have never really monitored it before, since I had never loaded it like this before.

lwmcguir
08-01-2012, 04:36 PM
I agree that forcing the transmission to shift into 6th will reduce the RPM's by 150 or so.

But reducing the RPM's does not improve the fuel mileage performance in fact, in my experience, it reduces the mileage performance.

I have a ScanGauge which is manufactured by Linear Logic. This instrument, which plugs into the trucks computer, provides many different readings on the status of the engine.

One of the gauge choices is to enable a real time fuel economy readout which I have used to validate the deterioration in mileage when shifting to 6th gear.

My experience has been that while towing on a perfectly level road at 55 mph and using cruise control in tow haul mode I will note the real time fuel economy. I will then force an upshift to 6th by disengaging the tow haul mode while continuing to use cruise control.

Immediately, the RPM's will decrease, but the real time fuel economy will decrease from what was being achieved in 5th gear.

Thus the benefit of a decrease in RPM's in this instance is being more than offset by an increase in the amount of throttle that is required to maintain the constant speed of 55 MPH in a higher gear.

Using cruise control ensures that it is a computer and not a foot movement that is changing the amount of throttle.

So in my experience, RPM's do not tell the whole story. We have always found this to be true when operating a tractor at near an overload condition. Shifting down a gear often lowers the fuel burn per acre hour. Lugging and engine rarely pays off.

Sandpirate69
08-01-2012, 06:05 PM
Normal operating temps for an Allison is 180F-220F. Mine usually runs about 200F when towing my rig on cruise control @70-75 mph on T/H mode. I've heard to downshift into 5th gear to get the trans oil to move faster through cooler, which in turn dissipates more heat. Personally, there's a larger tranny cooler that actually hooks up to the factory hoses. I will look for it again & post here for the Allison boys. :cool:

Westwind
08-01-2012, 06:30 PM
My 2008 D/A has the 6 speed and I will leave tow haul mod on until I reach highway speed and then I will disengage it so the Allison shifts into 6 speed overdrive and then I reingage the tow haul, I find I can squeeze better mileage out of the truck and the tow haul is engaged so if the grade gets too steep the Allison will down shift to handle it.
I've done this for 5 years and haven't have any problems - I feel this is an excellent engine transmission combination for what we do.

Birchwood
08-01-2012, 06:45 PM
I always follow the owners manual and never listen to a dealer .Whenever I tow my Landmark with my Duramax
the tow haul mode is on and also if its off the grade braking is off and you will wear out your truck and trailer brakes.

scottyb
08-01-2012, 06:49 PM
Normal operating temps for an Allison is 180F-220F. Mine usually runs about 200F when towing my rig on cruise control @70-75 mph on T/H mode. I've heard to downshift into 5th gear to get the trans oil to move faster through cooler, which in turn dissipates more heat. Personally, there's a larger tranny cooler that actually hooks up to the factory hoses. I will look for it again & post here for the Allison boys. :cool:

I talked to a guy today that owns a transmission shop in Austin and has a reputation for being an Allison guru. He confirmed what you are saying about temperatures. He said you can lower the temp some by running a synthetic oil in it. I am going to take it to him next week, to drop the pan and change the filter inside and the screw-on, and then fill it with synthetic oil. I would be interested in the larger cooler if you happen upon the name.

He also said they harly ever fail, and that I will have a hard time breaking it.

porthole
08-01-2012, 07:45 PM
Personally, I would skip the additional cooler. The D/A combo has a pretty good cooling system once warmed up.

Put the bigger pan on, that adds 4 quarts and a easy access drain plug.
Once you add a deeper pan and corresponding filter and a good synthetic you may not have to change your fluid for a long time.

Just change the spin on yearly or twice a year depending on the amount if your towing.
The Allison with synthetic can handle 240+


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porthole
08-01-2012, 07:46 PM
And your not going to lower the temp with synthetic


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Terry H
08-01-2012, 10:35 PM
All Allison transmissions in GM vehicles come from the factory with synthetic transmission fluid.

Hastey
08-02-2012, 08:06 AM
All Allison transmissions in GM vehicles come from the factory with synthetic transmission fluid.

to further add to what Terry just said is that if you are now running anything but the DEXRON VI synthetic. I advise change it immediately. Also, carry a spare quart or two with you in case you have to add. You just don't walk into a quickie mart and pick that up.

I've had my Allison out of my truck. It's no fun at all. I had to hire a guy to help me. Even GM puts two mechanics on it at a 12 hour shop rate. 14 hours of labor to put a $9.00 front seal in. Oklahoma Panhandle sand will eat them out of there quick.

The cheapest I found a shop to do it was $1200 plus parts.

porthole
08-02-2012, 09:40 AM
As long as we are on the D/A subject.
Long warm up idle times in cold weather are not good for the trans cooler lines.

Unless there has been a change, when cold the cooler circuit is also open, no t-stat to block the flow. That means cold thick trans fluid is still flowing (and at a good rate) through the lines to cooler and back.That is why you see so many cooler lines leak in the colder states.

The crimped hose ends on the cooler pipes can't handle s the pressure over the long haul. Replacing the 3 lines at over $100 each does not solve the issue.
There are aftermarket lines avaible that are superior the the factory items. If you have leaks, get the good replacements.

In 80000 miles I changed one line three times, one twice and the third I never did because it was too difficult.
Then I found out about the better stuff :cool:

dave10a
08-02-2012, 10:18 AM
The dealer indicated I could take it out of this mode when we get to highway speed. I have had a question in my mind about what is the proper way to utilize this and what is best for my truck. Any comments and recommendations would be welcome.

Thanks,
Harry

When a someone makes a comment that you don't completely understand, one should always ask why :-)

porthole
08-02-2012, 10:39 AM
5]I am still new to the RVing life and have a question about towing our rig. We have a Chevy Silverado 3500 with Duramax Diesel and Allison transmission. My question is regarding the tow haul mode for the transmission. Should we leave the truck in tow haul mode the entire time we are towing? The dealer indicated I could take it out of this mode when we get to highway speed.


When a someone makes a comment that you don't completely understand, one should always ask why :-)

Don't talk to anyone in the sales about your trans, including "service writers" at the desk. Your best bet is to talk to a tech that actually works on the vehicle and knows how the systems work.

The D/A combo are a terrific pair, well synced with computer controls. One of those controls is the T/H mode.
A few things are happening when you push that button. Line hydraulic pressures are increased so that the transmission clutches are able to keep pace with the load, up and downshift points are raised allowing the engine to do more work in the optimum torque range and most significant is that the torque converter is locked up from 2nd thru 6th.

Locking the converter means all the torque is going to the drive axle and not lost to torque converter slippage. The side benefit of locking is the fluid will run cooler since the heat build up is mitigated by not having the convertor slip.

In the non T/H mode the convertor still locks up, but not until 5th and 6th gear.

So what some folks are doing is getting up to speed but finding the truck is not shifting into 6th because of the programmed higher shift point. The converter is still locked, but switching off the T/H for a moment allows the truck to shift to 6th.

Your best bet when towing is to use the T/H mode. The trans will shift better with less slippage, the fluid will stay cooler, and that along with the less slippage means it will also last longer. Switch on and off if you desire to get into 6th gear.
And your engine/exhaust braking will work way superior with the convertor locked (think manual trans)

If you are not familiar with how the convertor works the easiest explanations is this.

Take two box fans and face them towards each other. Turn one fan on low, the other fan will start to spin, although just a bit slower because air is spilling off the fan blades.
Quickly switch up to high speed. The other fan will catch up, but because of the rapid increase of air flow even more air will spill off the blades and the 2nd fan will not ramp up at the same rate or speed.

Convertors work the the same using a fluid (that's why they are aka fluid drives). There are two "fans" inside a sealed housing, one attached to the crankshaft, one to the trans input shaft.
This liquid coupling and slippage is what allows you to stop at a red light and not have to disengage anything. The flow of fluid coming off the crank side is low enough to not work on the trans side. Step on the gas, spin the sucker up and the fluid starts to drive the trans.

[/SIZE]

Hastey
08-02-2012, 11:19 AM
In the non T/H mode the convertor still locks up, but not until 5th and 6th gear.


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I have the monitor screen in my cab for my Edge Performance Programmer. One of the things I monitor is the transmission and on my 5 speed and it shows the converter locking in 2nd gear on up. I'll forget to turn the T/H on after we take off and I can instantly tell that its off. It also shows me a % the torque converter is slipping while running.

porthole
08-02-2012, 04:30 PM
I have the monitor screen in my cab for my Edge Performance Programmer. One of the things I monitor is the transmission and on my 5 speed and it shows the converter locking in 2nd gear on up. I'll forget to turn the T/H on after we take off and I can instantly tell that its off. It also shows me a % the torque converter is slipping while running.

Got it - so let me quantify my comments with this - I should have prefaced my comments with 2006 and above, as that was when the Allison got a major overhaul and extra gear (although if you really feel like, you can add the 6th to yours.

So with your 2nd gear on up, is that in T/H or not?

Hastey
08-02-2012, 09:11 PM
Got it - so let me quantify my comments with this - I should have prefaced my comments with 2006 and above, as that was when the Allison got a major overhaul and extra gear (although if you really feel like, you can add the 6th to yours.

So with your 2nd gear on up, is that in T/H or not?

That is in t/h and I did not know I could add the 6th gear...........:confused:.......this is me thinking about spending money.....divorce.....weighing it all out.......money....wife kicking @$$.....I think I'll stick with the 5 speed.