View Full Version : 500 Mi Breakin Tow - Good & Bad
My wife and I decided to take a drive and get those 500 miles at 50 MPH out the way, so we took off from Henderson, NV and headed west for the Outlet Center just west of Barstow...aprx. 150 miles, with our 5500lb TT. The westerly half of this drive has a couple of real good, long grades, especially Baker headin' east.
The Good - Compared to my old 6.2, I could hardly feel the TT and had power up the kazoo. Got 14.4 MPG round trip. Truck had 3100 miles when I started, so I was pleased with the fuel economy this early in the game. Temps were solid the whole trip, except up Baker grade, the tranny hit 220 for a bit, but not too long.
The Bad - When in cruise control, not in tow mode, when starting to climb a grade and the speed dropped to about 47-48 MPH, the Allison downshifted 2 speeds and immediately spun from 1500 RPM to 3100. Scared the s**t out both of us! It then seemed to realize this isn't right, and shifted back down to 2000 RPM. This happened time and time again, even with the converter locked out. Using tow mode was better as the truck would never shift...stayed at 2000 and crawled up anything. But, it doesn't like to shift into tow mode with cruise control at 50. You have to get out of cruise and take the torque off the tranny to allow it to shift to tow mode. Well, that would be ridiculous to do all the time.
So, what seemed to work best, when coming to a grade, is to take it out of cruise control. The tranny worked great. Downshifted 1 gear at a time, and was perfect. I think when we start normal towing at 60 to 65 MPH, we will be up in the horsepower curve a bit more and maybe cruise control would work fine and the tranny wouldn't have to downshift at all?
Any comments, suggestions, or insight would be very helpful as to what towing methods works for you. Man, I love this Truck! :D
FirstDiesel
08-17-2003, 06:44
If your towing why aren't you putting it in Tow/Haul and leaving it there??
I find that towing up a grade in tow/haul mode
at about 2500 rpm and 1000 egt's works best
once the rpm's get down to the 1800 rpm level
or lower you have to follow it down with either
the o/d lock out or a lower gear - bringing the rpm up and the egt's down. In stepping on the brake in tow/haul mode you begin to lock in higher
rpm's - the braking feature - if it scares you pop out tow/haul and then back in again - it will adjust shift.
Towing up a grade is a job - Tow/Haul mode -
O/D lock out and in - and the shift lever. Keep those rpm's up over 2200 and the egt's below 1300
It is Rocket Science!
I love my D/A - It requires you to become a student of Torque and Horsepower. If you are just
willing to be a passenger - take the big hills at
35mph in 2nd and 3rd -t/h - o/d out and keep the rpm between 2200 and 2500 - and don't let the towing hype of these pages let you wonder.
I drive with the juice in level 2 - with gauges and my last installation will be a 4" flow thru exhaust to get my egt's down by 100 to 200 I hope
FirstDiesel
08-17-2003, 09:10
I guess I'm a fan of the KISS method. I hook up the trailer and drive. On flat roads it's in normal and in the hills it's in T/H and I drive.
Larry!
I guess I agree with your approach - It is still important to keep the RPM's up and the EGT's down
Which then requires additional steps -
That's about as simple as it gets!
Simple is always best - peachin
AbqGeorge
08-17-2003, 10:46
trip,
I'm a bit confused.
"....Truck had 3100 miles when I started. "
Why are you driving 50 mph at this point? The 500 mile break-in period is for the very first 500 miles. It has nothing to do with towing other than they recommend you don't during the first 500? At 3100 miles your ring and pinion is nicely broken in. The "sweet spot" on the D/A is around 68 to 72 mph. Add a bit of Juice (level 2) and you seldom shift out of OD. Put it in T/H and cruise and listen to your favorite CD or radio station.
I must have read it wrong - too!
There are two 500 mile break-in periods?
1. the first 500 miles of driving
2. the first 500 miles of towing?
As for the "sweet spot" I guess it's true
on level towing - but can you maintain
this on a 5 mile 5 - 6% grade - heavy hauling
(which I would define between 15,000 to
22,000 CGVW)
I don't have the answers - maybe a few - I'm looking for feedback from them that are "walking the walk!
Trip,
In Tow/Haul mode the Allison will not shift into 5th until you hit about 60mph. When T/H is off, it will hit 5th at 50. If you pull much of anything at all, your truck won't likely hold overdrive on hills at below 65 or 70. The rpms are too low.
I pull a 9500 lb camper and didn't like all the shifting in and out of overdrive so I "Juiced it". It very seldom drops out of OD now. On long hills, I force a downshift to keep the rpms at 2200. That keeps the exhaust temps down. I usually tow with T/H on. If I am on a flat road where traffic keeps me to 55, I sometimes turn off T/H so it will shift to 5th.
The Duramax/Allison doesn't shift like anything I've ever had before. It does some quirky things sometimes and it took a little getting used to but I love it. smile.gif
Continue to enjoy,
Lee
FirstDiesel - This truck doesn't seem to need the extra RPM on flat or near flat grades with our trailer. I want to keep the Rs down to increase my fuel economy and, over the long haul, make the engine last. That's why I'm not running T/H mode all the time, but that is an option worth considering.
AbqGeorge - The manual on pg 4-64 does recommend "...during the first 500 miles that you tow a trailer, don't drive over 50 mph..."
Peachin & glclary - Good info...if I remember right, max torque was around 2100 and only went down slightly after that as horsepower increased, so what you said makes good sense.
Thanks for all the responses and the help. We finished our 500 miles yesterday by going in the other direction into Utah. On the way home we made our 500 mile goal, and brought her up to 65 and was turning about 2000 RPM. This was much better, downshifts were one at a time and less frequent. Can't wait to go to Tahoe on Labor Day. Thanks again for the feedback! :D
I keep the RPM's as LOW as I can within reason. I run in the Juice's torque band (1700-2200peak) and my EGT's tay low. While the addition of RPM from a downshift will, in some cases, lower EGT's, if you step it down hard like the cruise tries to do to make up, the EGT's will get high...
We have around 8,000 miles on our truck pulling various trailers. Can tow at about any speed but have found our truck is the most efficient (meaning best mpg's and lowest EGT readings) when run at 1,900/2,000 rpm range which equals somewhere between 63-65 mph .... the faster you run it over that setting, the more fuel she uses, get over 70 mph (which she can easily run) and she really gets thirsty. Have also found that in reasonably flat country, use of the cruise control has little impact on mpg's. In hilly/mountain driving use of the cruise will cost you mpg's....Jim
DURAMONSTER
08-18-2003, 16:41
Originally posted by JEBar:
We have around 8,000 miles on our truck pulling various trailers. Can tow at about any speed but have found our truck is the most efficient (meaning best mpg's and lowest EGT readings) when run at 1,900/2,000 rpm range which equals somewhere between 63-65 mph .... the faster you run it over that setting, the more fuel she uses, get over 70 mph (which she can easily run) and she really gets thirsty. Have also found that in reasonably flat country, use of the cruise control has little impact on mpg's. In hilly/mountain driving use of the cruise will cost you mpg's....Jim This is exactaly what I have came across also.
Yup! Me Too - I feel the same way -
I'm glad Kennedy brought up the rpm
curve - for the juice - I have always enjoyed
his "BS" and found most of it to be true -
He has done it and is doin' it!
Now that I have some good advice of where the "sweet spot" and on cruise control (thanks to all), what about EGTs? I'm not going to add any boxes, truck stays stock, but will do alot of towing in some pretty steep country, but never plan on towing over 65 mph. Do I need a gauge to keep an eye on EGTs?
a64pilot
08-19-2003, 06:45
Trip,
If you leave it stock, you can't hurt it IMHO. But if your the type of person that likes to know what is going on in your engine then gauges ae nice, but not necessary if it's stock.
Turbo Al
08-19-2003, 10:19
Yes two breakin recomendations
first 500 miles
AND
first 500 miles of towing.
Your Ring & Pinion are NOT broken in untill you tow!!
Did I just hear a bunch of OPPS's???? :eek:
Originally posted by peachin:
Yup! Me Too - I feel the same way -
I'm glad Kennedy brought up the rpm
curve - for the juice - I have always enjoyed
his "BS" and found most of it to be true -
He has done it and is doin' it! The turbo is also a MAJOR key here...
In T/H my truck won't shift into OD until 65-70 mph and that is in cruise or out. If you want the truck in cruise and want it shift before the higher speed simply turn of the T/H and let the trans shift and then turn T/H back on. No need to turn the cruise control off. When towing I want the torque converter locked all the time possible. This method has worked great and with the juice towing at 65 mph I get no down shift on grades except the steepest ones or very long ones, even in cruise.
This truck has made me lazy. Put in cruise and T/H with juice on level 2, enjoy the scenery, watch the gages and traffic and let the truck do it's work. This truck is so smart that it will figure out what it needs to do if you will just leave it set. The trans somehow seems to figure it all out.
I also agree with JE Bar and Duramax on the tow RPM and speed giving best fuel econonmy.
Did I say I love this truck?
Tom
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