Scissor jacks may be good for changing a tire but I had the bright idea that I would alternate back and forth with one to jack up my car to maximum height so I could do some exhaust work. This involved using pieces of wood to build up the base for the jack. The higher I got the harder it became, and I couldn't figure out why. A plastic ring popped out of the jack with enough force that it could have taken out my eye. And then the car collapsed off the jack opposite from where I was working. Here's a pic:
The jack is destroyed, that plastic washer ring is gone from where the jack is turned and one of the legs popped out of the base. Basically the higher you go the harder it is to balance and the more pressure that comes from that. Keep that in mind if you ever have such a "bright" idea like I did. I ended up buying a floor jack that can roll to keep its balance. Still it's always possible for the car to pivot if you are going back and forth and don't watch the opposite jack and the back tires (both back tires were chocked both ways but the one on the side I was working came up off the ground, and I suspect the other jack might have tilted, not sure which happened first).
I'm now looking for a single point to jack up both sides of the front of the car at once. Any suggestions? I will need to remove one of the tires so I can't just drive up on ramps (which I also have).