Possible transmission problem on 1991 Volvo 740

Hi: I just bought a 1991 Volvo 740 GLE Wagon with around 280000km. It worked perfectly fine by the last owner. I took it home and drove it for around an hour on a hilly trip. At one point I was stopped at a red light, and when I tried continuing the car would not drive. The engine was running fine, but the car would not move. When I switched to 2 it did not move either. When I finally switched to 1 it continued driving. Shortly after, the car would not drive at all in any gear, not even Reverse. As of Sunday when I brought the car to the mechanic to look at, the car is driving fine. He even took it on an intense test drive and he could not find any problem at all. The only thing that I could have done was perhaps switched to 2nd gear while going at around 70 miles per hour, for a few seconds. Can you think of what could have caused this to happen and then now they cannot find any trace of the issue? Thanks for the help.

Asked by for the 1991 Volvo 740
I don't have the amswer to this fault, But i would like to say that the same thing has happened to me. i have a similar year 740 with similar milage.on my 1st long drive in the car, the transmission started to slip and then lost all drive in all gears. I pulled over, shifted through the gears with no effect. Turned the car off and started up again and away it went for 20 minutes. Gear changes were sometimes smooth, sometimes rough. Plenty of fluid in auto. If you have found the issue, i'd love to know about it.
2 more answers
These transmissions have issues with the overdrive relay sticking, but that just affects 4th gear. The kick-down cable is another common problem, it normally affects the shifting, but I would have that checked, make sure it is not binding.
Intermittently not having any gears sounds like a transmission, but your mechanic sounds good, they will figure it out when it does act up.
apparently the auto transmission clutched begin to flake off on these older models, clogging up the oil filter, which in turn stops the oil flow thru the torque converter which means no drive output to the wheels. This can be temporarily helped by an auto trasmisiion oil change, and cleaning out the filter, but that is a bandaid solution. Really it's an auto-rebuild.
Sorry... but i know through experience.