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Discussion Starter #1
This was probably covered but, I havn't come acrossed it yet....

My 2003 with 21,000 miles has an intermitant glitch that bothers me. Every once and a while when coming to a stop light/sign... the transmission gives a bump just before the truck stops....sort of feels like you are bumped from behind....what causes this???

Thanks
DRG
 

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It's the Ally dropping to first gear. A common problem in the early models - I almost got out of my truck to punch the guy behind me once! There's a TSB and a reflash to resolve it. I dunno the number - but your dealer should know if you tell them the problem.
 

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My truck does that as well. I also seem to get a false nuetral, kinda stuck between gears till i give it a little throttle. Maybe I need to have a reflash as well. Anyone have the TSB #? I wonder if that will be free or If I have to pay...
 

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It was free when I had mine done in May of 2002.

AHA! found it on a Google search:

Service Bulletin

Bulletin No.: 02-07-30-020
Date: May 2002

Chevrolet/GMC

Technical

Subject: Harsh or Delayed 2-1 Downshift, Neutral Feel at a Stop, Shift Busyness, DTCs P0708, P0847, P0872, P0875, P1711, P1713 (Reprogram TCM and, if necessary, Reprogram, PCM)

Models: 2001-2002 Chevrolet and GMC C/K 2500/3500 (3/4 and 1 ton) Series Pickup Models (Silverado and Sierra)
With Allison® Series 1000 Automatic Transmission (RPO M74)

Condition: Some customers may comment on a harsh or delayed 2-1 downshift, a neutral feel at a stop or shift busyness (excessive shifting). Upon investigation, the technician may also find one or more of the following DTCs set:

• P0708
• P0847
• P0872
• P0875
• P1711
• P1713
These new calibrations will address the following conditions:

2001 2002
Delayed 2-1 downshift at a stop 2-1 downshift quality concerns
Flare and bump on low speed coast-down and throttle reapply Cold shift quality concerns
2-1 closed throttle neutral feel *Shift busyness
Harsh 2-1 downshift DTC P0708, P0847, P0872, P0875, P1711, P1713
Shift busyness 2-1 closed throttle neutral feel


Correction: Reprogram the Transmission Control Module (TCM) with the new service calibrations, which were available from the Techline starting March 24, 2002 on the TIS2000 version 3.5 or later. These calibrations are electronic calibrations and are NOT available from GMSPO.

Important: 2002 Vehicles with 8.1L Engine---
If the concern is shift busyness, the PCM must also be reflashed to gain maximum benefit from the new TCM service calibration. This calibration was available from Techline starting March 10, 2002 on the TIS2000 version 3.0 or later. If the concern is not shift busyness, this step is not required.

This additional step is not required on vehicles with a 6.6L engine (RPO LB7) or 2001 vehicles with an 8.1L engine (RPO L18).
 

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"Bump"

I've got a new 06 and I'm getting this same problem ! It does
not occur when it is cold. It's driving me crazy ! Some members
here think a break in is required and the transmission is still
learning but I'm beginning to have my doubts.
 

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Could also be a dry yoke spline.When your stopping the suspension dips then recoils and you can feel slight bump when the driveshaft moves in and out.

Worth a shot
 

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Bump before stop

Could also be a dry yoke spline.When your stopping the suspension dips then recoils and you can feel slight bump when the driveshaft moves in and out.

Worth a shot


I called Allison direct and the engineer says to take it
to the dealer. It has a sticky valve. I'm aggravated at this but
at least he gave me his name and direct ph# to give to dealer
for technical assistance.
 

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I called Allison direct and the engineer says to take it
to the dealer. It has a sticky valve. I'm aggravated at this but
at least he gave me his name and direct ph# to give to dealer
for technical assistance.
If it had a sticky valve you would have a code most times. First thing I would do is put a Tech 2 on it and clear and reset the TAPs. Allison can do this and so can your dealer or any shop with a Tech 2.
mike
 

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My '01 had this same issue until the dealer re-flashed the PCM.

Everythings A-OK now.
 

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Discussion Starter #10
Took the truck into the dealer this morning....tech drove it and of course could not duplicate the problem...said that he checked the settings and the tranny had the latest....was told to drive it and if it continues to give me trouble bring it back to see if it set any codes...

will this problem set a code??

thanks
DRG
 

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"Bump" downshift

Took the truck into the dealer this morning....tech drove it and of course could not duplicate the problem...said that he checked the settings and the tranny had the latest....was told to drive it and if it continues to give me trouble bring it back to see if it set any codes...

will this problem set a code??

thanks
DRG
I took it back this morning for a 2nd time and made them give me a loaner car. The technician called and said this was normal for an Allison. The
first time they dropped the pan, poked around and reflashed the
ECM. They obviously do not know what they are doing. I talked to
the Allison factory direct and they advised the dealer technician to call.
Will it throw a code if the solenoid is just sticking and not electrically
"open". I'm gonna hang tough. I just paid 40K for a truck..
 

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LONGHORN Dad, if it's only happening when it's hot it may be a leaking C5 piston.

As for your question about the solenoid the answer is yes and no. A code will set if the valve does not move enough to send back a signal within a certain amount of time. If it's just slow or moves just enough to send back a signal but does not stroke all the way it may not set a code.
 

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Transmission bump

LONGHORN Dad, if it's only happening when it's hot it may be a leaking C5 piston.

As for your question about the solenoid the answer is yes and no. A code will set if the valve does not move enough to send back a signal within a certain amount of time. If it's just slow or moves just enough to send back a signal but does not stroke all the way it may not set a code.


The Dealer called and said to come pick it up. They cannot do anything
untill it throws a code. They did acknowledge the bump. I called Allison
and they have opened a "case" on it and will be in contact soon to
resolve my issue. Talking about having a regional manager drive it.
I wonder, is there others out here that have a crew cab that is
experiencing the same feel ?
 
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