What is the worst mistake you made doing your own wrenching?

On my 1st gen, stupidly used a breaker bar to tighten the two long bolts holding the brake caliper on. No surprise that one snapped right off. Many hours later using my friends harbor freight drill press to bore a hole through the broken bolt and finding the correct tap screw at Fastenal, it was back together using the proper tools.

 

I am a hack wrench and work with apprentices pretty regularly. Owning your mistakes is part of the learning process. I tell the apprentices that and I will discuss mistakes. Only difference between me and an apprentice, is I get paid more to learn. If you can't admit fault for something you did then it's all ego.

 

Ever got a windshield out? Me neither.

I was probably 18 or 19 .......CAAARAAAAACK!!! Nothing really wrong with the old one, near new. Just redoing the body completely on an actually nice Datsun 510. I loved that thing. Engine was a runner for the day.....It was mechanically ok and wanted to replace the rubber seal on the windshield and broke it center top. Ugggg. I think I got one at the junkyard. I've broken my fair share of 6mm and 8mm studs. OH yeah I broke a banjo bolt once by overtightening - amazingly soft and weak.

 

During the replacement of a timing chain on my first car (67 Mustang coupe w/a 289 V-8), I dropped a bolt down the hole while installing the distributor. I convinced myself it made it all the way down to the oil pan and "believed" I was safe and proceeded on. The engine started just fine so I did the victory dance and headed down the road. The first bump in the road dislodged the bolt and it fell between the chain and the crank gear. Needless to say it never made it to the pan and destroyed both gears, the chain, the front timing chain cover and the camshaft. There are plenty more, but this was one of the biggies.

 

Installed a really used engine in a really used truck. Didn't bother to take the oil pan off and check things over first. After about 100 miles I heard a bang and lost oil pressure. There was a mouse nest in the motor and it plugged up the oil pump screen, broke the pump drive shaft. Would have needed to pull the motor again to fix it so she went to a kid taking auto mech. for free.

 

Worst thing, probably tightening a bolt at the wrong angle on my brand new fox shocks and ended up rethreading the hole at the wrong angle, making the shock sit funny. Had to re-tap the hole.