Originally Posted by Dave57210
The more important Q; What the heck are you doing that requires you lift it so high? Please say U R not going under there while its on a jack!
Define "so high" ? A typical floor jack tops out at 19" high. If you're lucky maybe 23".
I dunno about you, but that won't touch the frame on my stock height 2wd 2nd gen dodge.
One would assume that he'd use jack stands (which are readily available in heights over 19"..), but he has to pick the truck up somehow to get it -on- stands. (and no, lifting by the diff housing is both not good and not always an option for the work that needs to be done)
Now, to the OP's question - I don't agree with the rest. 5" of extra height (dont stack them!) isn't going to kill anyone. If not a single one of the naysayers on this thread have never put a stack of 2x4 or 4x6 on top of a floor jack, well, I'll eat my Tilley. Of course you wouldn't get -under- the truck while it's supported that way.
It's not the way I'd do it - but I've been working on cars that need high lift jacks pretty much as long as I've worked on cars. I'd normally say "head down to harbor freight, by their 2 ton high lift long frame jack. $150-200, 30+ lift." - except it's gone from the website now, so they may have finally stopped carrying them. I've worn out 2, and am my third (in 15 years). Might be worth checking if your local store still has some in stock, they'll know what it is (because they are like 4 feet long).
There are some other "quality" jack options, but they tend to cost significantly more $$. If a $500-1000 jack is an option, let me know and I'll dig up my notes.
If it's just occasional use, though, I'd say just buy the extension and take due precautions. They're not significantly different than the way many 2 post lifts are setup for truck adapters, which are also perfectly safe when used as designed. Sure, the arm chair mechanical engineer in me wants to go on and on about the side loading blah blah blah. But in reality, if it -does- fail (and you are lifting safely), worst that will happen is the truck falls straight down, on it's wheels. Hell, that's what happens if the hydraulics blow out in your jack while you're lifting, too. Maybe the jack will kick out a bit, with small but not insignificant force.