Fourth gear clutch(s) gone. The result of letting it slip too much OR the servo cover now leaks so badly that it won't hold the band or clutch. Try driving in 3 and see what happens. If no joy, it's for sure repair time.

Check the servo covers on the passenger side for evidence of fluid leaks. They will ONLY leak when the servo is applied, so you will leave a trail on the ground when that particluar gear is engaged only (I remember a Ford automatic we rebuilt once -- only dipped in first gear because the very narrow first gear servo cover gakset rolled on installation. Real pain the the sitting part to repair...)

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!