Clarification:
If one axle pops out of engagement with the side gear in the transaxle, that (nonengaged) side will just spin (because it's a differential), and
neither wheel will be driven.
Saw this happen on a Nissan Sentra (FWD) once, after a shop had replaced the clutch. The car worked fine for a few days, then suddenly there was no "go." Found out one of the output shafts had slid partially out of the trans.
The GM axles are retained in the transaxle with snap rings; I suppose it is possible for a snap ring to fail or be omitted. I didn't say it was likely - in fact it's probably very unlikely - but it is worth checking, before you bother pulling the transaxle out. Real test is: raise and support rear of car, rotate one tire forward and observe the other tire - it should rotate the opposite direction. If it doesn't, check axle engagement to the transaxle.
Do measure the stroke of the clutch slave cylinder as suggested, to verify that the external (hydraulic) linkage is working properly. Finally, if you determine you are going to pull the transaxle and replace the clutch, please read this: http://members.yourlink.net/dragon/parks/clutch.htm
Thanks. Stu shut up now
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[This message has been edited by StuGood (edited 07-02-2002).]