ZF Gearbox "Clunk" Noise

As a mechanical engineer my guess is the clunk is coming from where a spiral pinion gear is not set (either shims or crush washer is used) to the proper lash on a spiral cut gear. A few thousands off can cause quit a clunk. Seems I read a lot of posts with the same problem but ZF does little to rectify the noise....... I think it comes down to who assembled the drive.

Under your selector valve see if there is a orifice plug on your supply inlet. You can get them for a Air break line supplier or from a gear box marine like Karl Senner llc. You can add these plus to slow the flow of the fuild in your ahead and astern engagement. If you install one that is too small just slowy drill will the next size drill bit to the hole size if you drill it too big your be back a square . Once you get the right timing you want for take up time the shaft spins and engages your set. Looks like a triangle pattern under the selector you will have ahead A and B and astern A and B then the top will be your supply. Try that to slow your flow of fuild and banging should stop