Problem reverse gear 4.2 liter automatic transmission

To the community, I have a problem with the reverse gear on my V8, 4.2 liter automatic transmission. All driving stages can be switched as it should, the gears also switch through, even the reverse gear can be inserted. Nothing's happening, not even a jerk. Oil's controlled, right. Maybe the sliding box glued or something? What could that be? Thank you for your help. Greetings Jan.