Well, in that case you've got something wrong. I suppose theres is one degree of freedom, spin of the shock rod, that is pretty much unaccounted for.
Sorry, it's a bit hard to figure out what's wrong without any more details.
Are you modelling a true MacP, with a leading link and a lateral link, or a modern one, with a L type lower arm? If the latter then you need to look at the inner arm bushes, you cannot treat both of them as ball joints.
Cheers
Greg Locock