Lurch from park

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Mdubbed

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Occasionally, when I start my 2004 4x4 Tahoe, G80, 4L60 trans truck, it gives a little 'lurch' forward, even though it's in park.
Everything else seems fine, no noises or slipping or erratic shifts or anything.
I've read/searched most of the forum and haven't seen anything concerning this. Has anyone else experienced this?
 

dubyagee01

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My 05 Denali does it sometimes. Usually when its cold. Its not a lurch but a bump where it seems to try for drive for a split second.

It hasnt done it since I replaced the battery with a new one. Might have been a voltage fluctuation during cranking
 
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Mdubbed

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Thanks for the responses

From Merriam Webster's:

lurch
verb (1)
Definition of lurch
(Entry 1 of 5)

intransitive verb

1 : to move with a lurch suddenly lurched forward

Semantics aside, yes, the truck lurches or bumps (as dubyagee prefers), forward.

Mine does it as soon as it starts, not when cranking.
Seems like something internal to the trans, like a check valve bouncing with initial pump pressure or something.
Just wondered if it might be indicative of some imminent failure.
Seemingly not, as Illinois has experienced it for some time.
Maybe a trans expert that knows/has experience with it will chime in.
 

dubyagee01

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Not semantics my paranoid friend. My truck bumps. Yours can do whatever it wants.
 

Mudsport96

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No this is a Lurch

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But anyway... here you go an information bulletin


After Cold Soak Models:
2009 and Prior GM Passenger Cars and Light Duty Trucks (including Saturn)
2009 and Prior HUMMER H2, H3
2009 and Prior Saab 9-7X with Automatic Transmission

Some vehicles may rock or move slightly forward or rearward while in park at start up after cold soak. This condition may be accompanied by a clunk noise. This is a slight movement that is more often seen visually, rather than felt, when viewed from the outside and using the auto-start feature, if equipped.

This slight movement is due to the residual transmission fluid in the clutch packs that creates a partial apply on start up. This movement is stopped by the parking pawl and/or transmission fluid exhausting completely from the clutch packs.

This slight movement has no adverse affects on the transmission and no repair should be attempted. This condition is normal. This can be verified by comparing with another identically built vehicle under the same cold conditions.

To prevent this condition from occurring, the parking brake should be utilized as per the Owners Manual recommendations anytime the vehicle is parked.
 

Mudsport96

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No prob. My tahoe does it too, my old 96 blazer did with the first and 3rd 4l60s but the 2nd one didnt. The Silverado doesnt. So its hit and miss on the clutch pack bleeding down or holding fluid. But, as soon as the pump makes good pressure everything goes back to where its supposed to be in park.
 

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