3T40 Autmatic Transmission suddenly won't engage Drive or Reverse

This transmission shifted smooth and strong through all gears until today when it stopped all of a sudden to engage either Drive or Reverse. No previous signs of slippage, hesitation, stalling or lack of power whatsoever.

We checked the linkage to the transmission and it works as intended, nothing loose or broken, everything is in place. If there was something slightly different with it from other similar vans we have then it had a slightly delayed engagement in Drive (it took a second to engage it after you moved the lever) - on all other vans we have the transmission go into Drive almost instantly.

Van is a '92 Pontiac Trans Sport/Chevrolet Lumina APV with the 3.1L V6 Chevy TBI engine with the 3T40 automatic transaxle.

Any idea on where we should start tackling this issue?

If fluid level and condition of fluid, is ok, I'd drop the pan and look for metal in the pan.....

Did this happen while driving, or all of a sudden you went to start the car, and it wouldn't move?

Fluid level is ok.

We parked it and after we got back there was no reaction in either Drive or Reverse.

GM manual for 95 transport lists the follow, should be very close to 93:
No drive in all ranges:
oil level-check and correct
torque converter- converter to flex plate bolts missing
oil pressure-pressure regulator valve sticking in bushing
-worn pump seals
-oil pumps shaft broken
differential-differential damaged or broken
drive link-broken drive link
-object between drive link and sprocket
manual valve- fallen out retainer clip
manual linkage-misadjusted
input shaft-loose or broken away from forward clutch drum
reaction carrier-broken at low roller clutch cam
You say you have verified fluid level proper, and shift linkage connected and adjusted proper, I think those are the only external checks. Suggest dropping the pan, and checking for broken parts. Pay particular attention to transmission filter and grommet holding it in place-it might be damaged, allowing air rather than oil to be drawn into transmission. Not sure if you can pull side panel off, if so you might be able to see drive link, check to see if broken. If, after all this, it looks like you may have to go really deep to find out what is wrong.
Jeff

Yes..'93 3t40 is like jeff indicated.
I'll verify for more info in my '93 manual but in the mean time take some inspiration from these...
www.avigex.ca/xport/3T40auxvalve.jpg
www.avigex.ca/xport/3T40controlvalve.jpg
www.avigex.ca/xport/3T40diagramm.jpg
www.avigex.ca/xport/3T40rev.jpg
I wish you can solve this problem

See the hardware involved in these 3 conditions:
Drive range first gear: Converter filled, Forward clutch, roller clutch holding
pressure to F. clutch, Governer, 1/2 shift valve, 1/2 accumulator

Manual Lo: (converted filled), forward clutch, Lo/reverse clutch
pressure to F. clutch, 1/2 throttle valve,, 1/2 shift valve, Lo/reverse clutch

Reverse: (converter filled), direct clutch, Lo/reverse clutch

I had that problem with my Grand Prix. The trans was rebuilt using the stock torque converter a few months prior.
The car lost all ranges . The torque converter bearing was destroyed sending metal through the trans. THe filter picked up the metal and no fluid pressure.
He replaced the converter with a 2500 stall speed unit. Much better driving at low speed..

Definitively solved the problem by swapping the transmission with a known good one.

Now the TCC has gone south (it comes on ragardless of speed, stalling the engine).

Does anyone know how to fix it without too much hassle with taking the subframe and transmission down again?

TCC normally comes on with an electric command. SO...I first suspect something happened in the wiring or computer logic......???
First unplug the TCC wiring from the transmission

http://www.avigex.ca/xport/3T40tccplug.jpg

..then TCC should be off all the time.....if not, something has gone haywire within the transmission solenoid.

If pulling the plug does remove the TCC....I would install a switch on the wiring to be able to apply TCC at will, like on the open road....it would give time to consider a definitive option later....if needed...

Thank you LMP! Alreayd unplugged the TCC and the engine doesn't stall at low speeds now.

I have found a documented repair of the TCC on this page (in german).
http://www.transsport.net/index.php/reparaturen-umbauten/reparaturen/94-94er-ts

Doesn't seem all that difficult, would give it a try once the weather gets better in this side of Europe.

OK then it proves the problem is in the electrical command, outside the transmission....
THough I do not speak german, the link you posted deals with the inside of the transmission. I'd think the source of your problem is not part of this procedure..

.....well...a test can be sone to verify if problem is in or out of transmission.
As said, the ON command comes from the computer. But the solenoid is connected this way: one of the wires is +12V...ALWAYS present with key ON. THis is normal. The other wire , other side of the solenoid coil, is GROUNDED by the computer to activate TCC. There is a remote possibility that the ground is made inside the transmission...faulty/chaffed wiring, as I say, very remote possibility. THis can be tested with an ohmmeter, one probe on either of the 2 wires of the transmission TCC connector and the other probe on ground/transmission body: a low ohm reading (0 to 30 ohms)would tell a ground fault inside the transmission. Open Ohm reading or very high ohm reading which is without a consequence (possible through lightly conducting fluid) tells everything iselectrically OK inside.

The solenoid is bad. It is not a problem outside the trans. I have seen this on my 3t40 trans of my APV as well as on both my 80's Buick Regals and when I had a 92 Beretta. The inside of the solenoid collapses over time onto the shaft causing it to stick. Once the trans get warm, the solenoid engages but doesn't release. If you are handy you can dis-assemble the solenoid and drill it out a bit. Or just replace it. If you replace it the problem and come back after a time. Leaving it unplugged affects gas mileage to the downside. You can take the side cover off to get to it without having to take frame members off. The hardest part is the wiring. I just cut the wires and soldered them back together. I'm sure crimping the wires would be okay since the wire splices are not subject to moisture.

..... Once the trans get warm, the solenoid engages but doesn't release......

That is relevant! Excellent.