Following the design changes on the Valiant models, the Duster also received a new hood, grille, front fenders, bumpers, and taillights for 1973. The taillights on previous years mounted from the inside and had a flush appearance. Starting in 1973, the taillights were mounted from the outside and were trimmed in chrome. These remained unchanged through 1976. New U.S. safety regulations called for 5-mile-per-hour (8.0 km/h) front bumper impact protection that was accomplished through a shock absorbing and stronger bumper rail with rubber guards.
Simpler single-piston slider-type disc brake calipers were introduced for 1973 (standard on 318-powered cars and with power-assist on 340 models), replacing the Kelsey Hayes four-piston calipers. Disc brake-equipped Dusters now had the more-common 5 lugs on 4.5" wheel bolt pattern. All 340 and some 318 engine-equipped cars received the simplified 8.25" rear axle assembly (with wheel bearings riding directly on the axle shaft and endplay being take by C-clips); these axles also featured the 5-on-4.5" wheel bolt pattern. (This axle assembly replaced the 8.75" "drop-out" arrangement seen on some 1966-'72 A-bodies). The 225-powered cars retained the 5 lugs on 4" pattern on vehicles with the standard drum brakes. All models received larger front wheel bearings and increased spindle diameter. Electronic ignition became standard across the board.
A new, metal sunroof was optional for 1973. The rear window defroster/defogger was upgraded to an electric-grid style for 1973, which replaced the previous recessed package shelf air blower.
Source: Wikipedia, 2012