Duramax/Allison Downhill Breaking

rturnrvn · February 16, 2005

03 LS ext cab. using Hypertech Power Programmer in stage 1 program pulling 15,000 lb. plus/minus. In Tow mode with OD locked out the engine breaking is supposed to control downhill speed. It does that but with too much agression. At 45 MPH the allison will downshift to 2nd gear and the engine speed almost pegs out "4500 rpm". Had to select Neutral and free wheel down the 5% to 6 % grade. How can i avoid this from happening. Have been told that 4500 RPM is in safe zone but really seems to be straining the engine. Is the info above a problem or acceptable parimeters.

Thanks

Jerry

bluenote · February 16, 2005

The ecm/tcm programming will force an upshift before it will over-rev the engine. It is a bit shocking when it revs up really high, but it will not hurt anything.

mamachala · February 16, 2005

You might try getting on the throttle a little to make it think you don't need to brake. I had the same experience and busted a baffle loose in the muffler, luckily it was under warranty. It will really scream sometimes, more than I want.

Jack

Shawn T · February 16, 2005

This is kind of ironic. Five years ago, before Allison came along, there was no such thing as grade braking. That was the downfall of an automatic transmission. Now they have an excelently engineered tranny that is the best of both worlds and people are complaining again. I have the D/A combo and I tow around 15,000 lbs about two or three times a year. There is a simple solution to this "problem". Either speed up to 50 mph or back off to 40 mph. I just can't see this being an issue. Buy a 6 speed and then you can select your own gear.

silverado3500 · February 17, 2005

This is kind of ironic. Five years ago, before Allison came along, there was no such thing as grade braking. That was the downfall of an automatic transmission. Now they have an excelently engineered tranny that is the best of both worlds and people are complaining again. I have the D/A combo and I tow around 15,000 lbs about two or three times a year. There is a simple solution to this "problem". Either speed up to 50 mph or back off to 40 mph. I just can't see this being an issue. Buy a 6 speed and then you can select your own gear.

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As Timothy already said, there is a simple solution. Buy a 6 speed. The allison is a great tranny as far as slushboxes go, but even with the all the computer programming, the transmission still has no way to know what is in front of you. Only you, the driver can plan ahead, with a manual, you can change gears as necessary for the road conditions, and you can take into account factors that the auto cant, such as rain, beginning or ending of a descent or incline. They can make a computerized transmission that shifts great, and handles a load well, but it is still a blind system. Thats why we're the drivers.

2jranch · February 17, 2005

Why would you "put it neutral and free wheel and go down a 6 degree slope". What's wrong with a little brake pedal. Even the big trucks with "jake brake" use brakes to maintain a down hill speed. Free wheeling is really stupid, especially on grades. "nuff said".

rturnrvn · February 18, 2005

This is kind of ironic. Five years ago, before Allison came along, there was no such thing as grade braking. That was the downfall of an automatic transmission. Now they have an excelently engineered tranny that is the best of both worlds and people are complaining again. I have the D/A combo and I tow around 15,000 lbs about two or three times a year. There is a simple solution to this "problem". Either speed up to 50 mph or back off to 40 mph. I just can't see this being an issue. Buy a 6 speed and then you can select your own gear.

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Want to thank all of you for your input. I see my concerns were without merit. Just needed input on how to control this beast.

Dont remember complaining about the problem, was just looking for someone with experience. Couldn't get any info from GM on this subject.

On the other hand if i had wanted a 6 speed i would have purchased it at that time.

rturnrvn · February 18, 2005

Why would you "put it neutral and free wheel and go down a 6 degree slope". What's wrong with a little brake pedal. Even the big trucks with "jake brake" use brakes to maintain a down hill speed. Free wheeling is really stupid, especially on grades. "nuff said".

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I reserve my comment at this time. Thanks for your input.