Bonneville automatic transmission issue

Shentar

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So a friend of mine has a 96 Pontiac Bonneville. For years he's had a problem with the transmission. When the car is cold, it won't shift out of park. He has to wait for the car to warm up for the transmission to work. Keep in mind, this isn't really dependent on the weather, although it takes less time in the summer than it does in the winter. What exactly would cause something like this? His mechanic says he can't find anything wrong with it at all. I'm curious.
 

EyeMWing

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Many things, none of them working.
Won't shift as in the lever won't move, or won't shift as in the lever moves and the transmission doesn't respond?
 

Spectre

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Old and worn seals or passages/pistons/valves in the valve body or upstream in the hydraulics. Something isn't getting enough pressure or is bypassing when cold then seals up as the metal expands when the transmission heats up. Rebuild time.
 

Shentar

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06 Porsche Cayman S, 90 Miata
Won't shift as in the lever won't move, or won't shift as in the lever moves and the transmission doesn't respond?
Level will move, but the transmission doesn't respond.

=SpectreOld and worn seals or passages/pistons/valves in the valve body or upstream in the hydraulics. Something isn't getting enough pressure or is bypassing when cold then seals up as the metal expands when the transmission heats up. Rebuild time.
That being said, and based on the value of the car, its probably just best to use till it finally goes, right? The car isn't in good shape astheically (paint blotches, missing a mirror and huge scrapes down one side, headliner falling through, missing interior trim pieces). My friend has been driving it like this since 2006 or so at least.
 

Spectre

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I would also recommend keeping a fully charged cell phone to hand and a premium membership to AAA around. Eventually it'll die, usually at the most inopportune time.
 

EyeMWing

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Many things, none of them working.
Old and worn seals or passages/pistons/valves in the valve body or upstream in the hydraulics. Something isn't getting enough pressure or is bypassing when cold then seals up as the metal expands when the transmission heats up. Rebuild time.
This. That car will have a 4T60E transmission in it - you can rebuild it into a 4T60E-HD. You could also change over to a 4T65E(-HD) from a later model, but that's any sort of rebuild is likely past the point of diminishing returns. Even the 65E-HD units go bad eventually (just ask PunisherBass how much THAT sucks)
 
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