What causes tow bar failure? Most often abuse, and sometimes age. Folks with the tow bar industry say that the most common form of tow bar abuse is backing up, a definite no-no, or because of jackknifing the toad when a panic stop is made and there's insufficient or non-existent towed vehicle braking. The stresses placed on tow bar components because of these actions can severely compromise or kill your tow bar system. NEVER back your toad vehicle with the tow bar, it's as simple as that.
But what about age? At what age should you consider retiring your tow bar? Like the joke among us old folks runs, it's not so much the age, it's the mileage. Your tow bar is a lot like you: Every mile you put on the tow bar begins to slowly wear away at the joints. There's not any real practical "joint replacement" operation available for tow bars. At least once a year, experts recommend, push and pull on your tow bar, feel for looseness. If it feels loose, have it inspected by a professional.
What applies to the tow bar also applies to that all-important connecting surface to the vehicle: The baseplate. Here's an inspection habit for you. Every time you hitch up the toad car, grab those connecting points. Pull up and push down. You should feel "give" in the toad car's suspension system, yes, but never should you feel looseness or give in the baseplate or connecting bracket. If you feel any give or looseness, towing can put you a big risk. Don't tow, get it fixed.
Check out your tow bar manual for lubrication instructions, and follow the suggestions given. Tow bars and accessories need to be cleaned and lubed with regularity. And when you're not using the tow bar, store it away from the weather. Rust can cause you grief over the long haul.
Need a new tow bar system? Have a reputable shop do the install, and ask them to walk you through the hitch up procedure. Smart RVers will want to use their phone or video equipment to make a record of how its done for future reference. Keep a copy of the owner's manual in the rig and in easy reach.