At 11:53 AM 6/4/2011, Rocket J Squirrel wrote:
>Would such a jack be helpful when working on a not-level car? I find
>that when all four tires on on the ramps, the van seems mighty stable
>and high enough off the ground for me to feel comfortable.

It's more stable than before...probably.  If you've spiked those
ramps into the ground then definitely; otherwise you're still
depending on ramp-to-ground friction with the same vectors
involved.  But.  From your numbers I'm guessing you have to raise the
wheels about six inches to level the vehicle.  That means your
driveway is about a thirteen per cent grade, or a bit under four
degrees.  Your Westy at gross weight is shoving 5300 lb straight
down, but the driveway is converting that to about 350 lb of
horizontal vector.  This total doesn't change just because you've
transferred the sliding surface from the tire patch to the bottom of the ramp.

Once you start lifting things up in the air, it gets hairier, and the
problem is that the vectors get worse in a hurry if things start to
go.  So if it starts to move and lift one side of the jack stand or
jack, the horizontal force will rapidly increase and either squirt
the stand out or slide the vehicle and topple the stand.  Even if it
just starts to roll, you're dead meat if you can't leap out of the way.

I'm with Scott.  Find or build a flat place to work, or get out from
under.  Not that we care about you or anything, but reading gory
stories can ruin your morning. ;-)

Yours,
David