The 1985 Wagons had the push button 4WD. The 1986-91 Wagons had the viscous coupling in the driveshaft instead. Neither car had a true center differential, but the viscous coupling acted as one. Making a sharp turn on pavement with a 1985 4WD Wagon will cause binding in the drivetrain and force the tires to slip, since there's no diff to compensate for the different wheel speeds in the front and rear axles. Someday I'd like to get a 4WD Wagon, and I want to combine the viscous coupling with an '85 tranny (if it's even possible) to get the best of both worlds.