Mazda Repair: suspension/shocks on Mazda 626, health food store, mazda suspension

Question
My Mazda 626 station wagon, year 1999-2000, is riding very low over the rear wheels.  Examination by two mechanics gave the diagnosis that I should replace the shocks.  I replaced first the left shock, which seems to have improved the ride somewhat, and the knocking sound which was there before has stopped.  

But the left side of the car, where the shock was replaced, is riding at least one inch lower than the right side, where it was not replaced.  And I would say that the right side is also riding very low, as though the car was heavily loaded.

I understand that the original owners of the car, a health food store, did a lot of driving with pretty heavy loads in the back.

Can you tell me what is happening here?  I would not think that replacing the shocks would affect how high the car rides, as the two mechanics seem to believe, but what do I know?  However, my feeling is that some other part of the suspension is at fault.  

HOw is this Mazda suspension?  Torsion bars or coil springs?  Can you explain why it is riding so low?  Is there something called adjusting the shocks to make the ride higher?

thanks for any help and explanations you can give me.
regards,
david troutman

Answer
shocks are either gas charged or oil charged if they are worn out and have lost whatever it is charged with it'll cause the car to ride lower then normal also check for broken springs they can also be a cause of the noise or worn shock mount which if your replacing shocks you should replace anyways as they wear about the same and what needs to be removed to replace them is already off when replacing the shocks.

push on the corner of the car with force and see how much it bounces 2-3 times is alright anything more is a key sign of shocks being worn out not the best test but for a backyard it's all you got. for the spings jack the car up removing the load off the springs and with force move them around hit them with a rubber hammer you'll hear if there broke it'll make and odd sound that just doesn't seem right.

you can also visualy check the shocks for leaks.