2001 audi quattro tt had problem sometime changing gears while driving it would sound like gear box fell out. Wouldn't go back into gear. Kill the engine and restart gears would work. Why?

SOURCE: audi a3 1998 automatic transmission cannot shift into gear

if a standard check clutch

SOURCE: Transmission Fluid. Pontiac G6. 2006

The trannsmission is a sealed unit and there is no dipstick. Check to see if you have a leak. More than likely it sounds like your low on fluid at least a 1/2 to a whole quart. Since these are sealed units it should be taken to the dealership to have looked at. If there is not any leaks then I would add 1/2 qt of tranny fluid and try driving so see if it helped. If it helped a little but the same problems are still there add another 1/2 qt. If it doesnt solve the problem then your tranny needs to be looked at.

SOURCE: my audi tt quattro 2004 model yesterday stopped changing gears

Release bearing problem.Change the clutch Assembly

SOURCE: 1998 saturn manual transmission will not engage in any gear

Well, there is one thing for sure the trany is damaged. You will be further ahead looking for another junk yard trany rather than worry about what is going on inside since there is probably parts and pieces inside that would still give you trouble without completely overhauling it, plus a junk yard trany, standard would be easy to come by.

SOURCE: Audi A3 2.0 tdi sport(2005 "55") Clutch/1st & reverse gear

sounds like a bent tooth on a syncro gear in the trans