Yea, the supports gotta be just right. But also, if you are working and change the weight distribution in any way at all, that shit can come crashing down. For example, removing a wheel and tire. Pulling the transmission. Hell, even draining the oil out of the pan could change the point of balance and you're fucked. I'll never work under a 2 post. Fuck that noise.
You set the supports, lift the vehicle about a foot off the ground, jiggle the hell out of the vehicle to try to knock it off the lift. If it survives that, you're safe. A popular mechanic on YT Rainman Ray does it every time for safety.
I've seen videos on yt of cars that have been sitting on a 2 post for days getting worked on and all the sudden they come crashing down. Too risky in my book when you have a 4 post alternative that is a bazzillion times safer.
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