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Help, several times I have found my 07 GMC Duramax 1-2 feet farther down my driveway from where I parked it, rolled backwards. Once I parked, shut it off and about a minute later while finishing a conversation with my wife the truck rolled about 2” back. I called a buddy who is a GM mechanic and he said there is no way that the truck can roll in park, its either in park or it will roll away immediately, I certainly believe him.
Then the other morning I found my truck about 4 feet from where I parked it, (yes I was stone cold sober when I parked) I took it straight to the dealership and they said it checked out fine, I’m stumped. The truck only has 51000 km (32000 miles) on it. I’m not crazy and no one is playing pranks, and no its not parked on ice. I was told at the shop to use the park brake, I don’t feel like that’s a fix but I don’t want it rolling across the sidewalk again either. My driveway is a slight slope and there was no sign of the tires sliding where it stopped, thinking it’s a creeping movement like what I felt when sitting in it. Anyone heard of this let me know please.
 

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Please fill out your signature. The parking pawl spring is known to get weak on some Allisons, and it slips. The 2001-2005 Transgo full shift kit has an improved pawl spring fix in the kit, plus does wonders for the rest of the tranny as well. The 2006 and up Allisons are supposed to have the improved parking pawl, and other issue fixes stock. Hope this helps, Wade.
 

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Discussion Starter #6
Surely the parking pawl either engages or dosn't, once the weight of the truck is on it I cant see it disegaging letting the truck roll a bit and reengaging. I wondered about the transfer case but that would either be in neutral and the the truck would roll untill it was stopped or it works properly.
 

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Do a test---- find a hill, stop the truck, place in park, then take your foot off the brake. If it rolls back, the shift lever is not engaging the pawl all the way.

By the way--- April 1 was last Thursday! :rof
 

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Please fill out your signature. The parking pawl spring is known to get weak on some Allisons, and it slips. The 2001-2005 Transgo full shift kit has an improved pawl spring fix in the kit, plus does wonders for the rest of the tranny as well. The 2006 and up Allisons are supposed to have the improved parking pawl, and other issue fixes stock. Hope this helps, Wade.
have you even seen the insides of an allison? What you just said about the park pawls is hog wash. They are known to get weak??? Those things are MASSIVE and are designed by allison to hold 30,000lbs parked on a sloped grade all day long.

ben

here is a picture. I dont have small fingers. It is way bigger than anything you will find in ANY other car or truck automatic transmission.
 

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I have no idea, I have never heard of it happening before. Maybe the park pawl isnt engaging fully. There is a spring that forces the park pawl "out" and into the output planetary carrier but if that spring isnt pushing hard enough maybe its not grabbing properly.
 

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Do you have a kid? Around the age of 15 or 16?
 

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It is all mechanical. If you stop and place the shift lever into park position, it is possible that the pawl is on the space between teeth and not engaged into the park gear. Then when you exit, the vehicle may roll a couple inches as the pawl drops into the park gear. Normal operation of all automatic transmissions.

It will not roll 3-4 feet! The only way it will do that, is if the linkage is way off and not moving the park shift rod into the park position, (I doubt that or you would have other issues) or you left it in reverse/neutral and exited the vehicle and only the engine compression was holding it.

Did you test it like I suggested on the above post? No-??
 

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Discussion Starter #15
I have no idea, I have never heard of it happening before. Maybe the park pawl isnt engaging fully. There is a spring that forces the park pawl "out" and into the output planetary carrier but if that spring isnt pushing hard enough maybe its not grabbing properly.
If the pawl isn't engaging properly could it slip and re-engage, allowing the truck to roll a couple inches like it did when I was in it???? I called 4 local GM servive departments and GM's customer service center, no one had heard of this, which is good and bad. My kids are tiny and I have two keys, both on me.
 

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maybe you sleepwalk out and move your truck in your sleep..i've strangled a lamp infront of my dad when i was younger and use to steal his shoes just about every night while i was sleeping..its possible.
 

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Discussion Starter #17
The spring does not push the pawl out-- it does the opposite-- it pulls it away so it does not engage into the gear. The shifter shaft moves a internal shift rod and that rides against the pawl- when you shift into park it pushes the pawl into the park gear. It is all mechanical. If you stop and place the shift lever into park position, it is possible that the pawl is on the space between teeth and not engaged into the park gear. Then when you exit, the vehicle may roll a couple inches as the pawl drops into the park gear. Normal operation of all automatic transmissions.

It will not roll 3-4 feet! The only way it will do that, is if the linkage is way off and not moving the park shift rod into the park position, (I doubt that or you would have other issues) or you left it in reverse/neutral and exited the vehicle and only the engine compression was holding it.

Did you test it like I suggested on the above post? No-??
The linkage was all checked at the dealership by a personal friend who checked it from to to bottom. The transmission works flawlessly, seldom moves much after putting it in park. To test it as sugested I think I'll park it half way up ramps, leave it over night, or a few days on the weekend, block it so it can't leave the property and see what happens.
 

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Discussion Starter #18
maybe you sleepwalk out and move your truck in your sleep..i've strangled a lamp infront of my dad when i was younger and use to steal his shoes just about every night while i was sleeping..its possible.
Buddy, my wife is like a little dog, not annoying like a little dog (thank god), but she dosn't miss anything......I can't sneak out, trust me.
 

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It is all mechanical. If you stop and place the shift lever into park position, it is possible that the pawl is on the space between teeth and not engaged into the park gear. Then when you exit, the vehicle may roll a couple inches as the pawl drops into the park gear. Normal operation of all automatic transmissions.


actually, no. If you take an allison apart, and you'll find TWO separate springs in the allison park pawl setup. The second one that forces the pawl out into the output planetary carrier isnt visible in the picture I posted. ;)



or you left it in reverse/neutral and exited the vehicle and only the engine compression was holding it.
thats impossibe. Engine not running = pump not turning in the trans = no line pressure = impossible to apply any clutches/hold the truck back.

ben
 

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The linkage was all checked at the dealership by a personal friend who checked it from to to bottom.
they might have checked the linkage going TO the trans from the shifter (ie, the shifter cable)...but I 99.99% guarantee they didnt check the linkage in the trans or the park pawl setup itself.

ben
 
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