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Old 02-22-2009, 04:38 PM   #1
mtheo
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Allison trans, anybody have this problem

I have an 2002 dura max, and was wondering if anybody had this problem.
I was going down a fairly steep grade, in tow haul mode, the Allison kicked down a gear and the motor was turning about 3500 rpm and holding back the rig as it should.. Then for no know reason the Allison started free wheeling. I had to give it a little gas to get it to re-engage. Did this twice on the way home.
Anybody have any suggestion.
Any help wouuld be appreciated
Mark
 
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Old 02-23-2009, 08:19 AM   #2
goin2themountains
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Has never happened to me, but sounds scary enough. If you are sure it was freewheeling(as in neutral on shifter), if t'wer me, I would be scooting to a tranny shop or the dealer as quick as possible. Might the RPM run a little higher than 3500, and it kicked into a higher gear?
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Old 02-23-2009, 10:10 AM   #3
kilch123
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I don't have the allison, but on the Dodge forum I subscribe to, they talk about a 'torque converter lock in' while the exhaust brake is engaged. Does yours have that feature? It may be the wiring/control of the EB that's causing the torque converter to unlock
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Old 02-23-2009, 01:25 PM   #4
dsprik
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Mark, I have the same 2002 Allison you have. I have 162K on it. I have gone up and down the Eastern US mountains with my 3400. I have never experienced the tranny "letting loose", so to speak. How was your trans temp when this happened?
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Old 02-23-2009, 01:33 PM   #5
Trailer Trash 2
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Beleive it or not my 96 ford used to do that even if I was out of OD, if I was going down a hill and didn't touch the accilerator it would free wheel untill I taped the gas peddel, then stay hooked up for a while then do it again and if I touched the brake peddel it would unlock the converter right then. dont know why either.
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Pulling a 2004, 2980 RL an oldie but goodie.
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Old 02-23-2009, 06:16 PM   #6
mtheo
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It wasn't scary, but more of an iritant. The temp was not up either, just was AS if the tourque converter unlocked.
I call the near by Allison shop and will head down there tommorrow. They will hook it up to the computer, for $85.00 and hopefully be able to tell what is up.
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Old 02-24-2009, 02:27 AM   #7
Clyde n Deb
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There are a couple of directions to head on this one. First question might be has the filter been changed recently? More telltale will be checking for codes. Computer controlled. In and out of downbraking can be affected by tapping the accelerator. A good diagnostic check should reveal the problem.
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Old 02-24-2009, 10:08 AM   #8
mtheo
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Got back from the Allison shop. No codes showed up. They had never heard of this before. They drove it and didn't think there was anything wrong with it and the problem might be a wiring problem in the tow/haul switch.
Changed fliud and filter at 50K and plan to change filter at 75K.
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Old 02-24-2009, 12:55 PM   #9
gpats
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The allison has a feature that will protect the engine when it gets to the RPM range that will damage the engine--I think that it might do what you are describing--
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Old 02-25-2009, 04:09 AM   #10
mtheo
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Rpm's never went over 3500, which is below red line.
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Old 02-25-2009, 07:50 AM   #11
MacDR50
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From the Allison Site
Q. Automatic Grade Braking - What happens on ice if it downshifts and slips?
A. Grade Braking monitors the front and rear wheel speeds/slips and can determine if the vehicle is slipping. If this occurs, grade braking will be exited and the transmission will up-shift to the normal range depending on throttle position and output speed.

Could be an axle sensor issue? Just a thought.

Added on Edit:
Allison FAQ Site.
http://www.allisontransmission.com/s...tegoryID=11#85
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