a tongue 22 at each end thereof for fastening to the under carriage of the cargo bed b holes 24 are located on the tongue 22 to receive bolts 24 fastening to the under carriage of the cargo bed via supporting rails r commonly found on the cargo bed underside the air hammer 20 includes a base plate 26 which mounts onto the bight portion 18 a of the u shaped channel within the legs 18 b so that it nests within the hollow of the u shaped channel the base 26 fastens to the bight portion 18 a of the channel by means of fasteners 28 thus a hammer head 30 of the air hammer faces an underside of the cargo bed b the hammer head 30 of the air hammer 20 is the working surface which pulses against the underside of the cargo bed b as shown by the dotted lines in fig5 the hammer head 30 reciprocates between the positions shown in solid lines and dotted lines so that repeated blows are provided to the underside of the cargo bed b by motion of a hammer head along the direction of the double ended arrows z when the accumulator a of fig6 is delivering approximately 90 pounds per square inch of air pressure the hammer head 30 will deliver approximately 4500 blows per minute once the air system has been enabled manipulation of valve v 3 via the switch 4 will direct air to both air hammers 20 referring to fig7 the hammer head 30 is disc shaped connected.