B757 CAPT; DURING CLBOUT; PURPOSELY DISCONNECTED THE AUTOPLT; SELECTED CTL WHEEL STEERING; AND BEGAN TRIMMING AILERON AND RUDDER. VNAV WAS NOT ENGAGED AND THEY BLEW THROUGH THEIR ASSIGNED ALT BY 600 FT.

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ON A VERY UNEVENTFUL EVENING; WE LEFT DTW; FLYING THE PALACE 2 SID. AFTER A RWY 21C TKOF AND A SHORT VECTOR TO 235 DEGS; WE WERE CLRED DIRECT TO DUNKS; CLBING TO 10000 FT. AT ABOUT THAT POINT; WE WERE CLRED TO 17000 FT. AS WE PASSED 13000 FT; THE CAPT SWITCHED AUTOPLT MODES BY DISCONNECTING THE ENTIRE AUTOPLT WITH THE CTL YOKE PUSH BUTTON; THEN SELECTING 'CTL WHEEL STEERING' WHILE FINE TUNING THE AILERON AND RUDDER TRIM. NEEDLESS TO SAY; 'VNAV' WAS STILL DISENGAGED. VERY SHORTLY; ATC DIRECTED WE STOP OUR CLB AT 15000 FT; WHICH I SET INTO THE ALT WARNING INDICATOR WITH LESS THAN 1000 FT TO GO. AFTER RESPONDING TO A SECTOR FREQ CHANGE (HEAD DOWN); I LOOKED UP TO SEE 15400 FT ON THE ALTIMETER. THE CAPT SMOOTHLY MANEUVERED THE AIRPLANE TO A 2000 FPM DSCNT TO 15000 FT. HIGHEST ALT SEEN WAS 15600 FT. NO PLT OR ATC CTR RADIO XMISSION. UNDERSCORES 'AUTOMATIC APATHY.' I HAD SEEN AN AUTOPLT MODE LIGHT AND PERCEIVED VNAV TO BE ENGAGED WHEN SUCH WAS NOT THE CASE. SHOULD HAVE STAYED 'HEADS UP' AND DELAYED RADIO RESPONSE. XCHK OF MCP SAW THE 'LNAV ENGAGED' LIGHT; BUT DID NOT RECOGNIZE THE LACK OF VNAV.