I somehow misplaced my good one (spelled old) and finally checked at Sears for a reliable replacement (my original source), but they no longer carry ball chucks, just the tall variety with built in gauge for $20 ! So, I tried Harbor Freight and they have them for $2 -- yay ! However, most times I press it against a tire valve, I hear a little thunk as the ball post slips off the valve post .

Tuesday, I bought another thinking the first might be defective, but this one was even worse! So, I decided to take a shot at correcting the problem. I inspected the ball post and found there was very little indentation at the tip (to capture the valve post), plus one side sloped off as though mismanufactured (China). Soooo...

I opened the ball chuck, removed the post, filed the top flat to remove the slope (soft metal), used a sharp punch to indent the post center, and used a shallow tip drill to shape a mild cone.

I put it back together and tried it, but although the ball post no longer slipped off the valve, I'd removed enough metal from the post that the tire valve no longer opened (needed a thinner rubber seal :?)! So, went to Home Depot (with fingers crossed), picked up a 78ct package of four 3/16" soft rubber washers from a hardware fastener aisle drawer, and happily found that just two were enough to properly seal -- after which the little bugger worked perfectly !

So, I once again have a properly functioning ball chuck and the other'll go back to Harbor Freight (though since the return trip'll probably cost more than the refund value, I may just modify the other as a spare -- still got two washers ).

==================A Little Later==================

Just modded the other one, a pretty quick operation and now I've a spare !