Three problems related to differential unit have been reported for the 1998 Ford Ranger. The most recently reported issues are listed below.
Strong odor of gear oil was found coating some of the exhaust system and much of the underside of the truck floor and other components in the area of the differential. Pontential of fire or an accident resulting from seizure of the differential (from lack of oil ) is feared.
Driving on i90 west with no problems nor warning the rear end suddenly locked up completely, severing the driveshaft and rotating the differential so that it embeded itself in the spare tire (mounted under the vehicle). Result was an immediate loss of control, vehicle swerved to the left and ran off the freeway into the median. Rear wheels were completely locked up and un-movable. Investigated by wsp (report # 0570977). Clearly an extremely unsafe vehicle defect. Ford dealership (evergreen in issaquah, wa) mechanics all concurred they had never seen anything like it.
Rear differential locked up at 50mph, causing vehicle to skid and throw it off road down into an embankment. One occupant was injured. Vehicle was totalled. Dealer cannot duplicate the problem.