CESSNA P210 PLT HAS VACUUM SYS FAIL AND ACFT HAS ALT EXCURSION.

Narrative

ENRTE FROM BNA ARPT TO JQF ARPT; NEAR THE TIME STATED ABOVE IN CRUISE WITH THE AUTOPLT ENGAGED; I WAS GIVEN PERMISSION FOR HDG DEVS 'AS NEEDED' FOR NAV AROUND ACTIVE TSTM CELLS. DURING THE TIME I WAS CIRCUMNAVING A CUMULO NIMBUS CELL; THE ACFT ENTERED AN EXTREME NOSE DOWN PITCH ALT; EXCESSIVE BACK PRESSURE WAS APPLIED AND THE AUTOPLT DISENGAGED. AFTER THE AUTOPLT WAS DISENGAGED; I WAS ABLE TO REGAIN PITCH CTL AND RETRIM THE ACFT FROM ITS FULL NOSE DOWN SETTING. AS I WAS RETURNING TO 13000 FT; I NOTICED FALSE INDICATIONS FROM THE ATTITUDE INDICATOR AND NO SUCTION. THE ATTITUDE INDICATOR IS THE ONLY PRIMARY INST ON THIS ACFT OPERATED FROM VACUUM AND THE 'FCS' RECEIVES PITCH INFO FROM THE ATTITUDE INDICATOR. THE DIRECTIONAL GYRO IS SLAVED. LEVELING BACK AT 13000 FT I ADVISED ZTL THAT I HAD A VACUUM FAILURE AND NEEDED TO STAY CLR OF THE CLOUDS AS MUCH AS POSSIBLE. I WAS TOLD THAT THERE WAS XING TFC AT 12000 FT AND THAT A PLTDEV OF 400 FT HAD OCCURRED AND TO CALL THEM. THE FLT WAS CONTINUED PARTIAL PANEL TO JQF ARPT. MAINT PERSONNEL WERE CONTACTED TO TROUBLESHOOT THE DUEL VACUUM SYS. BOTH VACUUM PUMPS WERE FOUND TO BE SHEARED AT THE SHAFT AND THE VACUUM OUT INDICATORS WERE INOP. REPAIRS WERE MADE AND THE ACFT RETURNED TO SVC WITH A NOTE ON THE SHUT DOWN CHKLIST TO CHK THE VACUUM OUT INDICATORS AFTER ENG SHUTDOWN.