I have used an old Sears 2-ton floor jack for automotive repairs for over 40yrs. Always dependable, never needed maintenance. The other day I needed to check my brakes and used it to lift and remove a wheel. While the wheel was in the air I stepped away for a minute and when I returned the jack was all the way down. I pumped it up again and gave the handle an extra twist to snug the valve. I again had to step away and when I returned the jack was again all the way down. So I pumped it up a third time, giving the handle a real hard twist and just watched it. For around 20secs there was no movement, then suddenly the jack dropped down as if the valve had opened!!

This 20sec 'death timer' failure mode was very repeatable. 20secs is just enough time to crawl under for a "quick look", something I just maybe did a few times in my reckless youth. I hope we are all smarter than that now and know that jack stands and wheel chocks are your friends.

These old jacks are common and repair kits and videos are available. The reason for leak-down failures is usually not low fluid, but that the main piston seal becomes worn and stiff with age and develops cracking or clearance with the cylinder bore. My seal had not cracked which might help explain its unique malevolent behavior. All new seals and check valves exorcised those evil spirits.

 

Machines will kill you and not care.
There is no mercy in them.