I found this topic while searching for happijac maintenance. This is the best information I've found anywhere. Thank you for posting this!
I have happijac 4500's, 14 years old. I purchased this camper this spring and the jacks are in dire need of service. I have 2 completed and they work great. My problem with the remaining 2 is that I am unable to pull out the manual socket. I have removed the C clip and the sprocket is loose on the inside but the socket will not come out. I have tried everything I can think of short of welding in a coupler nut and using a slide hammer. The drawback to this is the socket will be ruined.
Any thoughts would sure be appreciated.