Drop the rear end cover plate and inspect the carrier housing for an oblong hole where the spider gear pivot shaft goes through it. It's a chronic problem area on rear ends from those years, and if the transmission has ever had a shift kit installed it's much more likely to happen.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!