1991 trans am stock automatic transmission
It drove fine yesterday but now every gear is like it’s drive. Pulled the pan off and linkage shifts okay. Not too sure where to go from here if anyone has any ideas?

 

Do you mean that when the Gear Selector is in:
-Park
-Reverse
-Neutral
That the Transmission operates as if the Gear Selector is in OD?

Or...
Do you mean that when the Gear Selector is in D1, D2, and D3...
That the Transmission operates as if the Gear Selector is in OD?

 

when reverse and neutral are selected the transmission still operates in drive

 

Help us understand here:

What position is the actual transmission shift linkage in when this is going on? As in, you put the "handle" inside the car into whatever, and the transmission just carries on as if you hadn't done a damn thing?

Afterwards, when you got up under it and watched the transmission linkage as your assistant moved the handle from here to there, what did you see? Did you see the linkage go from D to R to P to L to whatever, or, ... what?

 

If the Linkage is operating properly...

Either the Manual Valve of the Valve-Body, is disconnected from the Linkage, or the Manual Valve is Broken, or the Valve-Body has a Cross-Leak/ Damage.

 

Too many neutral drops, or aggressively rocking a car stuck in snow, will do that. "Rocking" the car will sometimes break them loose again. It should be a death sentence for a 700R4 but I had one do that, and it went 7 more years of daily driving after getting it unjammed.

 

or the forward sprag is gone

 

If the Input Sprag Fails...
The Trans will operate NORMAL with the exception that there will be no 3rd or 4th Gear operation.

The Gear Selector operation would be perfectly fine.

 

The 4L60E in my 99 Tahoe failed in this manner. It welded clutches together when it started to slip. ALL gears were forward.