Jeep

My old Jeep still runs well. I don't drive it much so it's still under 100K miles. In July I had an auto shop replace the left front axle because of a torn CV boot. (CV stands for Constant Velocity. It’s a type of flexible joint in an axle. A CV joint is covered by a flexible rubber-like “boot” that keeps the grease inside and the dirt outside.) Ever since the axle was replaced I've heard a faint tinkling sound from the left front wheel. It sounded like a ball bearing shaken in a glass jar. After several months of listening to the annoying sound, I took the vehicle back to the shop. At first, the mechanics were as mystified as I, but they found the source of the sound.
 
My Jeep has machined aluminum alloy wheels. Instead of a hubcap, there is a disc about 2 inches in diameter that covers the hole in the center of the wheel. With the cover disc removed you would expect to see the end of the axle, an axle nut, and a castellated nut cover with a cotter pin through the axle. The nut cover and cotter pin prevent the axle nut from loosening.
 
When the mechanic popped off the cover disc, the nut cover was lying inside the wheel! The original mechanic apparently forgot to install the nut cover, and being too lazy to remove the lug nuts, remove the wheel, remove the cotter pin, install the nut cover, replace the cotter pin, put the wheel on the axle, and install the lug nuts, he simply tossed the nut cover inside the wheel’s axle cavity and installed the cover disc. The tinkling noise was the metal nut cover bouncing around inside the wheel’s axle cavity. Unbelievable!
 
If the axle nut had backed off - and there were about 6 threads between the nut and the cotter pin - the wheel would have loosened enough to ruin the wheel bearing and hub race. When you take your vehicle to an auto shop, you're really rolling the dice.