United States 94V143000
THOMAS BUILT BUSES, INC.
The problem
A SUDDEN HYDRAULIC PRESSURE LOSS DURING HARD TURNS RESULTS IN A MOMENTARY LOSS OF POWER STEERING ASSIST. THE PRESSURE LOSS OCCURS WHEN THE HYDRAULICALLY DRIVEN ENGINE COOLING FAN TURNS OFF IN THE TURN.
Risk
THE DRIVER REACTS TO THE LOSS OF POWER STEERING ASSIST BY OVERSTEERING, WHICH COULD RESULT IN A VEHICLE ACCIDENT.
What owners should do
THE HYDRAULIC CONTROL VALVES WILL BE REPLACED WITH VALVES OF A NEW DESIGN. UNTIL SUCH TIME AS PARTS ARE AVAILABLE, OWNERS WILL BE INSTRUCTED TO DISCONNECT THE FAN CUTOFF SWITCH SO THAT HYDRAULICALLY DRIVEN FANS WILL RUN FULL TIME, ELIMINATING THE PRESSURE SPIKE.
Units 1150