A B737-300 ON CLBOUT AT 6000 FT TO 16000 FT WAS UNABLE TO TRIM NOSE DOWN. DECLARED AN EMER AND DIVERTED. NO MANUAL OR AUTOPLT TRIM ENGAGED.

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DURING THE CLBOUT WITH THE FO (ME) ACTING AS THE PF AT 250 KTS AND PASSING THROUGH ABOUT 6000 FT; THE ACFT WOULD NOT TRIM FORWARD. THE MOTOR ACTED AS IF IT HAD REACHED ITS MECHANICAL LIMIT; HOWEVER; IT WAS ONLY INDICATING ABOUT 3.5 - 4.5 ON THE TRIM GAUGE. THE ACFT COULD BE TRIMMED AFT; AND SUBSEQUENTLY TRIMMED BACK FORWARD; BUT WOULD NOT TRIM FORWARD ENOUGH FOR THE ACFT TO BE IN TRIM FOR THE 250 KT AIRSPD. OP OF THE TRIM MOTOR WAS SMOOTH; AND THE ACFT WAS FLYING WELL; BUT REQUIRED SOME FORWARD PRESSURE ON THE YOKE. BOTH THE FO (PF) AND CAPT (PNF) ATTEMPTED TO USE THE TRIM BUTTON ON THE YOKE TO TRIM FORWARD. THE CAPT COMMANDED A SHALLOWER CLB (1000 FPM) ON THE FLT DIRECTOR AND REQUESTED A LEVELOFF FROM ATC AT 13000 FT. I MAINTAINED 250 KTS WITH THE AUTOTHROTTLE ON. WE THEN AGREED TO A CLB TO 16000 FT AND A DIVERSION. WHEN IT BECAME APPARENT THAT WE WOULD LAND OVERWT; WE REQUESTED A DSCNT TO 10000 FT WHICH WAS GRANTED. BOTH THE CAPT AND MYSELF REVIEWED THE FLT MANUAL FOR ANY APPROPRIATE CHKLISTS INCLUDING JAMMED STABILIZER. THE CAPT ELECTED TO PERFORM THE VISUAL APCH AND LNDG USING A NORMAL CONFIGN OF 30 DEG FLAPS AND AUTOBRAKES 3 DEGS. IN ACCORDANCE WITH THE CHKLIST; HE ALSO ELECTED TO HAND FLY AND KEEP THE AUTOTHROTTLE OFF. AT NO TIME DURING THE FLT WAS THE AUTOPLT ENGAGED. WE ALSO ELECTED TO LOWER THE LNDG GEAR EARLY TO BURN DOWN EXTRA FUEL WHICH WAS SUCCESSFUL IN BURNING DOWN ENOUGH FUEL FOR A LNDG JUST BELOW MAX STRUCTURAL (113.9K ON FINAL). THE LNDG WAS UNEVENTFUL AND THE EMER (WHICH WAS OFFICIALLY DECLARED ON THE DSCNT) WAS CANCELED. TRIM THROUGHOUT THE REST OF THE FLT WAS USED 'JUDICIOUSLY.' MAINT WAS CONSULTED DURING THE FLT. THEY ALSO RECOMMENDED A LNDG SHORT OF DEST AND MINIMAL USE OF THE TRIM. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE NOSE DOWN TRIM WAS LIMITED AND AT 250 KTS HAD NO NOSE DOWN TRIM AT ALL AND REQUIRED FORWARD PRESSURE ON THE YOKE. THE MANUAL STABILIZER TRIM WAS NEVER USED AND THE AUTOPLT WAS NEVER ENGAGED. NO INFO WAS RECEIVED FROM MAINT ON THE ACTION TAKEN FOR THE TRIM RPT.