Why transmission not shifting

There could be a number of possible reasons why your G30 Chevy van is not shifting out of 1st gear. Some potential causes could include:

1. Faulty shift solenoids: The shift solenoids are responsible for controlling the flow of transmission fluid through the valve body, which in turn affects the shifting of gears. If the solenoids are not functioning properly, it can cause the transmission to get stuck in 1st gear.
2. Low transmission fluid pressure: If the fluid pressure in the transmission is too low, it can prevent the gears from shifting properly.
3. Faulty transmission control module: The transmission control module (TCM) is responsible for controlling the shifting of gears in an automatic transmission. If the TCM is faulty or has malfunctioned, it can cause the transmission to get stuck in 1st gear.
4. Internal transmission issues: There could be internal issues within the transmission itself that are preventing it from shifting out of 1st gear. This could include worn gears or clutches, or other mechanical issues.

It is recommended to take your van to a qualified mechanic or transmission specialist to diagnose the issue and perform any necessary repairs.

Even overheated transmission fluid would not expand this much. If too much fluid has been put in, it can begin to foam. You haven't mentioned any indication of air bubbles on the stick. It won't shift because you have too much fluid.

Too much fluid can damage the seals, yielding leaks. None of this is good news. Here is advice:

https://mechanicbase.com/transmission/slightly-overfilled-transmission/

Sounds like it maybe slipping, try checking the transmission fluid level and add as necessary to full mark of near full mark, which is in the operating range, could do what I did with my windstar minivan, add in the Lucas Transmission Fix, for your Ford Taurus you'll need Mercon ATF ( Automatic Transmission Fluid ) unless its a manual transmission or differently specified which then will need different fluid, check the owners manual, repair manual or phone Ford and ask them for transmission fluid type. Keep in mind that the wrong fluid type in transmission and or wrong amounts ( overfilled ) or ( underfilled ) can affect the transmission's proper operation.


Also check your coolant, when coolant level is low the light will come on the dash cluster and add as needed, Fords usually use the green coolant,green colored coolant or could use the universal type coolant. Check the owners manual, look in a repair manual or ask Ford technician for the coolant type.

Check transmission fluid level if low on fluid it will suck air and transmission forward clutch can not apply. If fluid is full and clean looking RED in color shift control solenoids are the problem and internal. BROWN and BLACK fluid indicates the forward clutch was slipping and now has no holding power for movement. this case the transmission needs reconditioning.

If the fluid is full and there are no external leaks, and it is still malfunctioning, I would try to flush and refill the transmission with new fluid to see if this rectifies the problem. If it doesn't, then there is a problem with a shift solenoid where the transmission will have to be reserviced and perhaps torn down and rebuilt again (I know this is dreadful). Try to see if there are any codes stored on the computer for the transmission that might point to a clue about the problem you are experiencing with it.

5 QUARTS FOR FLUID FILTER CHANGE. IF REPLACING TORQUE CONVERTER OR TRANSMISSION OVER HAUL. YOU NEED 13.8 QUARTS. WHEN YOU CHANGE FLUID AND FILTER.BESURE YOU HAVE TRANSMISSION FLUID LEVEL TO THE FULL MARK BEFORE DRIVING VECHICLE.LET ENGINE IDLE UNTIL GET WARM BUT CHECK TRANSMISSION FLUID WHILE ENGINE IDLING.IF FLUID LEVEL DROP A LITTLE ADD A LITTLE MORE TO GET FLUID LEVEL AT FULL MARK.ONCE ENGINE GET OPERATING TEMPERATURE.SHIFT TRANSMISSION THROUGH ALL GEARS TWICE ONE AT A TIME.CHECK TRANSMISSION FLUID LEVEL.SHOULD BE ON FULL MARK.DRIVE VECHICLE FEW MILES CHECK FLUID LEVEL.IF FLUID LEVEL.FULL YOU GOOD.IF STILL LOW ADD A PINT AT A TIME.ONCE FLUID LEVEL CORRECT. SHIFTING OKAY TIME PLAY.YOU GOOD TO GO.

SOUND LIKE TRANSMISSION FLUID LOW OR YOU NEED A TRANSMISSION FLUID AND FILTER CHANGE.THE 4T40E OR 4T45E IF YOU DONT SEE TRANSMISSION DIP STICK.BEST TO DO A FILTER AND FLUID CHANGE.YOU NEED 7 QUARTS OF TRANSMISSION FLUID A NEW TRANSMISSION FILTER AND PAN GASKET.I WOULD BUY FILTER AND PAN GASKET AT DEALERSHIP.YOU NEED A LARGE DRAIN PAN TO CATCH TRANSMISSION FLUID.IF YOU HAVE A TRANSMISSION DIP STICK. BEFORE YOU FIRST BEFORE STARTING THE ENGINE CHECK TRANSMISSION FLUID LEVEL ON DIP STICK.SHOULD BE ON THE FULL MARK.IF NOT ADD FLUID TO FULL MARK.THEN CRANK VECHICLE LET IDLE UNTIL ENGINE HOT OPERATION TEMPERATURE ABOUT 10 MINUTES.THEN APPLY BRAKE PEDAL.THEN SLOWLY SHIFT TRANSMISSION SHIFTER THROUGH ALL GEARS 2 TIMES.THEN PUT TRANSMISSION IN PARK.CHECK TRANSMISSION FLUID LEVEL.IF NOT AT FULL MARK ADD TRANSMISSION FLUID UNTIL LEVEL CORRECT.

CHECK TRANSMISSION FLUID SOUND LIKE VECHICLE SLIPPING DUE TO LACK OF FLUID. CHECK TRANSMISSION FLUID ON DIP STICK. WHILE ENGINE COLD FLUID LEVEL ON DIP STICK SHOULD FULL MARK.CRANK ENGINE LET VECHICLE IDLE TO WARM.THEN HOLD FOOT ON BRAKE SHIFT THROUGH ALL GEARS FEW TIMES CHECK TRANSMISSION FLUID LEVEL IF LOW ADD FLUID UNTIL YOU GET TO FULL MARK.IF YOU HAVE THE TRANSMISSION WITH NO DIP STICK.YOU NEED TO CHANGE TRANSMISSION FLUID + FILTER. YOU NEED 7 QUARTS OF TRANSMISSION FLUID.BUY DEALERSHIP TRANSMISSION PAN GASKET ITS THICKER MADE DIFFERENT WONT LEAK FLUID. THE TRANSMISSION GASKETS AT AUTO PARTS STORES TOO THIN LEAK FLUID BAD.

Trying changing your transmission fluid and filter. The fluid gets gummed up and causes very rough shifting. It may also be low as well. I would suggest a full back flush where all fluid is pulled out of the system including the torque converter whereas a simple fluid and filter change will not do that. Also, there is a transmission fluid filter on the transmission lines, it looks very much like an oil filter. I believe that will greatly help your problem.

Transmission is worn and previous owner has added transmission fluid additives like Lucas transmission oil to try to make it last longer. The fluid is burn and needs to be changed, best thing to do is to have the transmission fluid and filter changed and add some additives to the fluid and try not to drive it to hard.
It shift's hard when your driving at normal speeds because the fluid is thicker then it should and the transmission line pressure is higher due to the thicker fluid. At WOT the transmission slips so it seams smoother and that's why the fluid is burnt.
Good luck and hope this helps. Do not do a trany flush, the transmission is already worn out, but the dirty fluid will make it worst too.