Above the springs the W126 and W123 have rubber spacers... you should be able to see the rim of this rubber spacer (sometimes referred to as a shim) poking down from the top of the spring "pocket". On the edge of this spacer you should also be able to find a number of nubs.
For the front I believe you can get 1,2 or 3. Compare this with the back springs - here you can have 1,2,3, or 4 I think...
Now I'm not saying you need the same number on the front and the back - that isn't necessarily how it works - but if you happen to have 1 nub on the back and 3 on the front then you could be getting a bit of a wheelie effect.
If you want to see a bit about checking if your suspension is level I have gone through the FSM procedure with self made special tools (a bit of wood) for my W123 in this thread:-
How I adjusted the toe in / out, camber and caster on my W123 300D
Scroll to post # 4 - to save yourself some reading!
If this doesn't help then I guess the best way of sorting this out is to check the uncompressed length of your springs - this means taking 'em out... so before you get to doing complicated things check for simple things like wheel size and tyre sizes first.