The power from the trans goes through the over running clutch (ORC) and direct clutch in the overdrive unit. I have never seen a failed ORC and direct clutch in the over drive as long as the trans was assembled correctly. The same direct clutch and ORC is use daily in the diesel units as the gas units.

The direct clutch is also used in reverse and is used to slow the vehicle down on coast in forward gears.

The clutch that needs proper attention is the overdrive clutch because the correct shim must be used on the OD piston to time the release of the direct with the application of the OD.