A SAAB 340B IN CRUISE AT 17000 FT DECLARED AN EMER AND DIVERTED DUE TO FAILURE OF THE L DC GENERATOR AND SUBSEQUENT OVERHEAT WARNING LIGHT AND ENG VIBRATIONS.

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WHILE CRUISING AT 17000 FT MSL; ACR FLT XYZ FROM EVV TO DTW EXPERIENCED MASTER CAUTION ANNUNCIATOR IN CONJUNCTION WITH AN OVERHEAT OF THE L DC GENERATOR. PERFORMED EMER CHKLIST. AS INSTRUCTED; WE SHUT DOWN L DC GENERATOR. L DC GENERATOR LIGHT ILLUMINATED INDICATING GENERATOR WAS DISCONNECTED. OVERTEMP LIGHT EXTINGUISHED AFTER 2 MINS INDICATING TO CREW THAT OVERHEAT CONDITION HAD BEEN RESOLVED. MAINT CTL WAS NOTIFIED OF SIT. WE BOTH AGREED (ALONG WITH COMPANY) THAT FLT COULD CONTINUE TO DEST SAFELY AS VMC CONDITIONS PREVAILED ALONG OUR RTE OF FLT AND DTW. APPROX 10 MINS LATER; L DC GENERATOR LIGHT RE- ILLUMINATED. DISPATCH WAS NOTIFIED THAT FLT WAS DIVERTING TO INDIANAPOLIS; IN. THIS WAS AT THE DISCRETION OF THE PIC AND THE FLC AS A WHOLE TO DIVERT TO INDIANAPOLIS. THIS WAS BASED UPON THE FACT THAT THERE WERE NO MORE PROCS TO BE FOLLOWED. NOTIFIED ZAU OF SIT AND DECLARED AN EMER. SIMULTANEOUSLY; L ENG BEGAN TO VIBRATE WITH ASSOCIATED VARIATIONS IN TORQUE INDICATIONS. WE DECIDED TO KEEP ENG RUNNING AS ALL OTHER INDICATIONS (OIL PPP; TORQUE; ITT; NG) WERE RELATIVELY STABLE AND ENG WAS PRODUCING PWR. FLT PROCEEDED INTO INDIANAPOLIS; IN; WITHOUT EVENT. FIRE TRUCKS WERE PRESENT AS ACFT ROLLED OUT ON RWY 23R. WE BELIEVE THIS PROB AROSE DUE TO THE FACT THAT THE GENERATOR DRIVE SHAFT LOCATED ON THE NG (COMPRESSOR) SHAFT ACCESSORY SECTION HAD FAILED AND NOT COMPLETELY SHEARED AWAY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT WHEN THE MASTER CAUTION LIGHT AND THE GENERATOR OVERHEAT LIGHT CAME ON; THE GENERATOR WAS SWITCHED OFF WITH NO IMMEDIATE PROB AND WE CONTINUED ON AS SCHEDULED. THE RPTR SAID WHEN THE OVERHEAT LIGHT CAME ON AGAIN IT WAS ASSOCIATED WITH AN ABNORMAL ENG VIBRATION AND THE DECISION WAS MADE TO DIVERT. THE RPTR SAID WHEN MAINT STARTED WORK IT WAS DISCOVERED THE GENERATOR WAS COMING APART AND THERE WAS EVIDENCE OF DEICING FLUID ON THE INTERNAL PARTS OF THE UNIT. THE RPTR SAID THE RPTR HAS KNOWLEDGE OF AT LEAST 3 OTHER DC GENERATOR FAILURES ON THIS TYPE ACFT AND ONE OF WHICH CAME APART IN THE SAME MANNER.