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Old 10-27-2004, 03:04 PM   #1
Montana_2203
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2002 Duramax/Allison: 3400RL

Just curious if I should always keep the 'tow' button in when towing my camper... I am pretty sure you should but sometimes on level, long stretches of highway... as in I-95 southbound to Florida.... when you are up around 65mph.... it seems that it might be ok to engage the cruise.... however, I do not want to do anything that would mess up my truck... so, what's the consensus here?

2002 2500HD Duramax/Allison: 2005-3400RL

thanks,

 
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Old 10-27-2004, 03:16 PM   #2
Montana Sky
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I use the tow mode when towing in city traffic or bumper to bumper traffic on the freeways during rush hour. Once the I reach my cruising speed of 65 - 68mph I turn the tow mode off. If the transmission starts the game of searching for the right gear or hunting to find the gear I turn it back on. I also tow with the cruise on as well. You are correct, the long level stretches of highways are the perfect place to run in fifth gear. Just listen to your engine and it will tell you if you need to have it on or off. Also keep an eye on the trans temp.
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Old 10-27-2004, 03:37 PM   #3
Glenn and Lorraine
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Quote:
quote:what's the consensus here?
I concur with Montana Sky. With my 2500HD D/A I am in overdrive and on cruise control anytime I am on the open road such as I-95. I only kick it out of OD and cruise when in traffic or on a grade.
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Old 10-27-2004, 03:41 PM   #4
Montana_2203
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[quote]Originally posted by Montana Sky

I use the tow mode when towing in city traffic or bumper to bumper traffic on the freeways during rush hour. Once the I reach my cruising speed of 65 - 68mph I turn the tow mode off.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Ok, great... one other question.... this camper is heavy and although I think the truck is plenty for the unit.... does the 2500HD Duramax/Allison (mine is a '02 and has the tow package) generally come with all the stuff needed to do the towing... like trans cooler, oil cooler, heavy duty fan and all that stuff.... and although this is not a 'dullie' I have the proper tires and know about the proper inflation....I will check but I get the impression that you know your stuff so I thought I would ask here...
thanks......
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Old 10-27-2004, 04:10 PM   #5
Bill Hill
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You're really talking about 3 different things here: 1) use of the tow/haul mode, and 2) use of the cruise control, and the OD lock-out feature. Since you have the D/A, do you have boost & egt gauges? You really need both to tell you what your engine is doing.

First my thoughts on tow/haul mode. Use it whenever you're towing or hauling. It is designed to change the way the transmission shifts based on the additional weight, etc. It also engages the automatic downshifting mode, so that as the vehicle slows down, the transmission downshifts to act both as a brake (as much as an un-braked diesel will do) and to keep the rpms at the optimum level.

Use of the cruise control is something else. If you are on relatively flat terrain, it works fine, but you still need to be ready to kick out of it at any time, especially if you want to pick up a little speed to climb a hill.

The Over-drive lockout is the third component. This is where the pyrometer (exhaust gas temp gauge) really comes in handy. You can be in OD at 59 mph and 1850 rpm where the peak torque is, but you may be running much hotter than you want, like 1050-1150 deg F. If you kick it down to 4th you increase the rpm to about 2250, but your e.g.t. will go down about 200 degrees. This is a good thing.

I don't mean to sound like a lecture here, but this is something I struggled with for months after getting my '04 D/A. My first e.g.t. gauge seemed a little off, so I took it back to the installer. Turns out it wasn't right, but the new one read much higher temps. Took it back again, but it was right. The D/A does run a bit hot, so that's why you should have the gauge to help you adjust the throttle, tranny, etc. to get the maximum work with the least temperature.

Hope this helps, and I'm really not a hopeless pedant!
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Old 10-27-2004, 04:38 PM   #6
sreigle
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Are the GM's different than the Fords? I use tow/haul all the time when towing, without exception (well, occasionally I forget to turn it on) but also use cruise and keep it in overdrive all the time except when it shifts out on its own. I was under the impression the GM's could be done the same way. Tow/haul does not lockout the overdrive on mine. I've seen it running the same rpm at a given speed as when not in tow/haul. That's on level ground.

I figure if the tow/haul makes it easier on the engine and/or transmission then I'll keep it turned on.
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Old 10-27-2004, 04:58 PM   #7
Montana_2205
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Unless I forget, I always use the tow/haul mode. From everything my son and I have read, the transmission was designed specifically for the purpose of towing. The first time it was in tow/haul we were pulling the camper home from the dealer. As I was getting off the Interstate, it started downshifting as I let off the accelerator and pressed the brake pedal. It startled me at first, then I realized what it was doing. There is a short, but very steep hill about a mile from our house. The first time we went down the hill, it shifted down a couple of gears and the RPMs went up very high and I was a little worried, but I guess it was doing what it was suppose to do.

On our first trip, I used cruise control, but I soon learned that I could keep it from shifting as much if I was in control. It may be different on very flat roads, but I think I'll keep it off cruise control.

Scott
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Old 10-27-2004, 05:02 PM   #8
OntMont
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Quote:
quote:Originally posted by sreigle

Are the GM's different than the Fords? I use tow/haul all the time when towing, without exception (well, occasionally I forget to turn it on) but also use cruise and keep it in overdrive all the time except when it shifts out on its own. I was under the impression the GM's could be done the same way. Tow/haul does not lockout the overdrive on mine. I've seen it running the same rpm at a given speed as when not in tow/haul. That's on level ground.

I figure if the tow/haul makes it easier on the engine and/or transmission then I'll keep it turned on.
I do the same as you with my Chev. Someone once wrote "the Allison transmission is smarter than the average driver", so I let it do its thing. On those occasions when I forget to engage T/H mode, the truck still seems to perform OK, but I think I would rather have it T/H.
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Old 10-27-2004, 05:47 PM   #9
DHenry
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I only use the T/H in town or the hills, the rest of the time it is off. My Duramax tows my 3670 with ease. I do have the air shocks to level out the load though.
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Old 10-27-2004, 09:49 PM   #10
Montana Sky
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Steve,
The Duramax with the tow mode will also allow you to use 5th gear while engaged as does your Ford. I will clarify how I use the tow mode. When on flat highway roads I usually turn the tow mode off once the trans has shifted into 3rd gear. The only reason I do this is so that it will shift out of fourth gear sooner into 5th (O/D). I had found that if I left the tow mode engaged it will not kick into O/D until I reach 60-64mph bringing the rpm's into the high 2's. I dont feel it needs to hold the shift that long and that is why I turn it off to allow the 5th gear as soon as possible. I have never found a need to lock out the O/D yet. Another thought, the boost and EGT guages that were mentioned above, I am getting mixed stories on. Most of the dealerships I have talked with about these guages tell me I dont need them. As long as I keep my eyes on the tranny temp and engine temp that is all I need to know and worry about. Some say with the Allison transmission and all the computers onboard, they will set off a warning light long before any damage can be done. I am still considering having these two mounted on the pillar of the truck. Need to get more info before I do anything yet.
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Old 10-27-2004, 10:01 PM   #11
Montana Sky
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Speezack,
I have the 2005, 2004, and 2003 brochure here in front of me and this is what they say for the Chevy Silverado. If your truck has the Heavy Duty Trailering Package then you have the following, trailer hitch platform, seven pin wiring connector, auxiliary transmission oil cooler, trailer brake control harness and seven-way to four way adapter. I can tell you that I have the same truck and coach as you and have not had any trouble towing this coach. Been up and down a few mountain passes in Northern Idaho, Montana and Wyoming and the truck walked up and crawled down just fine without a hitch. In my opinion you have all the truck you need to tow the 3400RL.
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Old 10-28-2004, 04:59 AM   #12
tnorfitz
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I don't know about the D/A combo, but I have a 2002 GMC Sierra 6.0L that we are ready to trade in for a 2005 GMC Sierra CC 4X4 D/A. On the 2002, the tow / haul just adjusts the shift pattern. It hold each gear until higher RPM's are met. This makes it easier on the tranny by keeping the RPM's up. It will go into overdrive on straight stretches, but it likes to jump out of overdrive easier with a load being carried, or the slightest incline in the road. When we pulled our 19' Wildwood TT, we found it easier not to use the Cruise, but just monitor the speed manually. In certain cases, we even dropped it into '3' and travelled down the road at 65 - 70. I am looking forward to seeing how the new truck will work. I was told the Allison tranny in tow / haul also adjusts the shift pattern for higher RPM shifts, but also helps brake when you let up on the gas, which helps in downhill coasting. Can't wait. The truck comes off the production line this week.
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Old 10-28-2004, 09:13 AM   #13
padredw
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Quote:
quote:Originally posted by tnorfitz

I was told the Allison tranny in tow / haul also adjusts the shift pattern for higher RPM shifts, but also helps brake when you let up on the gas, which helps in downhill coasting.
I can testify from experience that what you have heard about the downhill is absolutely true. It is one of the best features of this engine/transmission team. In fact, I never use the tow/haul except in the mountains (or steep hills), but then we are towing a Montana 2955RL which is not one of the heavyer trailers. I also do not use cruise while towing. I tow in overdrive at about 65 MPH on level, faster downhill where legal and slower uphill.
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Old 10-28-2004, 11:53 AM   #14
Karl
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We have a GMC 2500 Duramax/Allison also. I do use the Tow mode when towing, however, I often will hit the button briefly to go out of tow mode to allow the tranny to shift into 5th just a bit sooner than it would in tow, then I go back to tow mode. I do this especially on two-lane roads where I will be driving at a speed just a bit below the "sweetspot" which seems to be 63 mph/1800 rpm on my unit.

There have been a few times in mountain driving, and more times driving against a severe headwind that I have used the "lockout" of 5th to keep the tranny from doing the seek and shift.

I did ask my dealer about my habit of undoing "tow" to allow the upshift, and he/they did not feel that that would be any problem.

I applaud GM/Chev for arranging the marriage of Duramax/Allison and hope they have many offspring!
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Old 10-28-2004, 01:58 PM   #15
sreigle
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Thanks everyone. I hope noone objected to a Ford guy asking a question in a GM thread. It was a legit question and I like to understand these things. Thanks for the replies.

Montana Sky, your GM gauges may be better than the Ford gauge. The boost gauge on mine works well so I'll just use the one on the dash. On the prior Ford I had pillar pod gauges for water temp, EGT, and trans temp. The dash on the Ford has water and trans gauges but they're glorified idiot lights. They work as gauges until reaching the normal range. They then sit in one spot until the temp goes above or below some preset threshhold. I want to know when it is starting to heat. The gauge moving to Hot is too late. Picked up the new truck this past Monday and have an appt this next MOnday to have the gauges installed. After watching those gauges on the traded truck I'm a believer. If your dash gauges work as real gauges then you probably don't need the aftermarket gauges.
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Old 10-28-2004, 10:22 PM   #16
Montana Sky
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Steve,
Thanks for the info. I think I will be checking into getting the EGT, boost, water temp gauges installed this coming spring. No need to spend the money now since the coach is in storage until spring.
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Old 10-29-2004, 02:44 PM   #17
tnorfitz
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Haven't gotten my 2500HD in yet. How do you lock the tranny out of 5th gear with the D/A combo? Is there a special button, or do you move the shift lever to a lower position. On my 2002 GMC 1500HD, there is no way to lock out overdrive, unless you shift it into '3'.
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Old 10-29-2004, 03:35 PM   #18
Karl
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All you do is hold the "Tow/haul" button till the little idiot light tells you it is locked out. Hopefully your dealer will take a drive with you to show you all the options. If he/she doesn't offer, insist upon it, and be sure to ask as many questions as possible. Remember, she is YOUR servant till the deal is complete---that means when the vehicle is in your hands and you are completely satisfied!
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Old 10-29-2004, 06:12 PM   #19
sreigle
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Tnorfitz, I meant to congratulate you on your new soon-to-be-delivered truck but got carried away and forgot. I think you'll like the engine/transmission combination. Although mine's a different brand, the help slowing down the vehicle on a downgrade is fantastic as I'm sure it is in the GM's. There have been times on twisty mountain downhills whre a line of vehicles ahead of us constantly are on and off the brakes that I've actually stepped on the brake just to let the cars behind us know that, yes, our brake lights do work. I know I don't like being in a tight downhill situation thinking the guy ahead of me has no brakelights and you just know a FW going downhill has to be using the brakes frequently. Enjoy the new truck.
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Old 10-29-2004, 06:50 PM   #20
tnorfitz
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Thanks for the info on how to lock out 5th gear. Now I am wondering if that works the same way on the GMC Sierra that I have now. Maybe it is just a function of the Allison tranny.
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