I did not get you by ( what you learned from that ) i have done the quarter car model using Using picture 1
The Y in the Above picture related to bump I have fixed both front and rear wheels and apply the Base excitation on the two front wheel This is the picture for the four Fixed support for modal Analysis

The total mass of the chassis was 469 kg I have used two springs Sprung mass stiffness ,Unsprang mass stiffness , I did not know the meaning of joints in the model And I have not include the spring rate