When I installed my Reese, it had 2 small rubber bumpers in the kit. They are about 1" in height and 1" in diameter. They sit under the head on the cross member (from leg to leg). If I tip the hitch head forward I can make contact with these bumpers and the hitch stops moving. There is just enough friction to hold everything in place.
These bumpers are nothing special. I suspect anything similar would work in their place. They just attach with 1 small 10/32 screw/nut onto the cross member in existing holes.
Bruce A. Wittmeier
2001 Ford F250 PSD, Ext cab, Shortbed, Island Blue/Silver, 4X4 Off-road, SOF Auto, Alum Wheels, Chrome Step, Line-X bedliner, Reese 16K slider, Jordan Ultima 2020, AirLift Airbags, Sunnybrook 30RKFS
I had a cluncking problem both when towing and when uncoupled. Switched to a gooseneck adapter and completely eliminated the problem.
Several manufactures are available. I selected the adjustable unit shown at gooseneckadapter.com because I needed a really short unit when pulling with a flat bed truck. Then easily adjusted for my standard pickup.