1988 Subaru Subaru

4WD STATIONWAGEN GL , AFTER ACCELERATING TO DRIVING SPEEDS, LOUD CLICKING OCCURS, IMMEDIATELY FOLLOWED BY RAPID INTERMITTENT LOCKING OF FRONT WHEELS, FOLLOWED BY FULL LOCKUP OF ALL WHEELS, FORCING VEHICLE TO SUDDEN AND COMPLETE STOP. ENGINE DOES NOT DIE, AND WHEN ACCELERATOR IS DEPRESSED, TRANSMISSION RETURNS TO NORMAL FUNCTION. DEFECT - EVEN AT LOWER SPEEDS OF 15-20 MPH, CAUSED SUDDEN LOCKUP IN TRAFFIC, NEARLY CAUSING 3 REAR-END COLLISIONS WITH FOLLOWING VEHICLE AND 1 FRONTAL COLLISION WITH BRIDGE WALL DURING 1 MILE TRIP TO GET VEHICLE OFF THE ROAD. PROBLEM SEEMS TO APPEAR AFTER ACCELERATION TO DRIVE SPEED IS DONE. ONCE SPEED STABILIZES, LOCKUP OCCURS, AND CAN BE MINIMIZED IF ENGINE IS SPED UP WITH ACCELERATOR, BUT ONCE STARTED, RESULTS AGAIN IN FULL LOCKUP ONCE ACCELERATION IS LET UP. THIS IS A HIGHLY DANGEROUS CONDITION THAT APPEARS TO HAVE ABSOLUTELY NO WARNING UNTIL IT HAPPENS. I SUSPECT IT IS POSSIBLY A CONTROL COMPUTER PROBLEM, A VACUUM-RELATED SYSTEM PROBLEM AND / OR AN INTERNAL TRANSMISSION PROBLEM. VEHICLE WAS IN 2-WHEEL DRIVE MODE AT ALL TIMES. NO DRIVING WAS ATTEMPTED IN 4-WHEEL MODE. I'M NOT SURE IF VEHICLE HAS ABS BRAKES, BUT THIS WAS A REMOTE CONSIDERATION ALSO. LOCKUP FELT LIKE IT STARTED IN THE TRANSMISSION/TRANSFER SYSTEM, THEN RELIABLY PROGRESSED TO A BUCKING MOTION OF ENTIRE VEHICLE, AND AFTER 3-4 FORWARD-BACKWARD OSCILLATIONS, ALWAYS PROGRESSED TO A FULL LOCKUP OF ALL WHEELS TO A SCREECHING HALT. AS SOON AS VEHICLE STOPPED, IT COULD BE DRIVEN ONCE AGAIN AS IF NOTHING HAD HAPPENED.