I took my Corsica 1993, 90K miles, to a mechanic to diagnose a problem (the car starts shaking sometimes when switching lanes on a highway).

The mechanic could not find anything wrong with the front wheels or steering, and said that he turned off the "transmission lock up converter" (I may have remembered this wrong), to see whether the problem is with the automatic transmission.

I could not understand from his words what this means in practice. I have a 1,000 mile trip in front of me this weekend - is it safe to drive a thousand miles with this thing turned off?

Many thanks in advance.