About the only place to put a single floor jack to get both front wheels off the ground at the same time is under the crossmember just behind the oil pan. If your floor jack has a small pad, it may dent the crossmember. So I use a jack with a large pad, and spread the load further with a wide block of wood.
I have seen some very trashed crossmembers, so I prefer to use two jacks under the spring pans or front jack points.
I concur, the crossmember directly behind the oil pan is the way to go. I put a piece of oak 2x4 about 12" long on the jack to distribute the load over the entire crossmember. Once up, jackstands go under the jacking points and away it goes.
As for the rear, the differential housing is your best bet. Once again, use a good piece of wood (something soft so it gives a bit), jack it up, and then put your jackstands under the rear jack points and your're good to go.
this gets complicated when i want to bring the whole car up level. (for trans/diff refills. i do it once a year. why not)
even tho i have a low-profile jack, and use 2x6 boards to roll-up on, its sketchy to get a jack under the diff when the front is raised. (i even have rhino ramps.) maybe im just chicken. i psych myself out of alot of work when it comes to lifting the spider. i always owned and worked on Jeeps, with lots of clearance. the spider , should it fall, has no room for survival of anyone underneath.
and frankly, who wants to take chances with a handsome face like mine.
but im getting more ballsy about it. most work is on the sides near the edge where my head doesnt have to be under the car
The other thing I always do is leave the jack under either the front crossmember or diff in addition to the jackstands just to provide an extra safeguard. Another thing that I do sometimes if I have the wheels off is to stick them under each corner of the car. So between the jackstands, jack, and wheels (if possible) there's a lot under the car to keep it up should something fail. Getting crushed under a car isn't high on my list of things to do either
I bought a low-profile jack from Sears, and just jack up one spring cup at a time in the front. Although you could do the crossmember with a piece of wood, I figure it's probably worth the extra effort for the added safety factor.
The Jacking points on the Spider seem too close to the center of gravity on the car. In the photo you can see I use heavy-duty stands, lifted near their limit. I have a great deal to do under the car, and I am a big fella', so...
I have never had a car shift while up in the air like my '81 Spider has. I am going to lower it a bit more than I would like because of this. I don't want the mass to move out past the jacks stability point. A very scary proposition.
Someone on another thread had cautioned when lowering the car, to lower the front or rear first?
In my case, I lower one notch at a time on each stand, using the spring cups in front and the trailing arm attach points in the rear.
It feels very nose heavy while resting on the standard jacking points.