Recently I noticed that the back of my Datsun 120Y is not even, one side is droped lower than the other, that is the right side is dropped lower than the left side. What is causing this and how can it be fixed??

I noticed the same thing on my car. I came to the conclusion that after 33 years of the driver getting in and out of the car that it had just sagged a little bit...

I dunno if that is the answer though.

Are both the rear wheels inflated to the same PSI??? I know it sounds silly but it could by why, but yeah like Loster said a driver getting in and out of a car for over 33years something may have worn

Cheers
Damo

I recently rebushed my door hinges, the bushes are still available from Nissan they were not that hard to do and made the doors sit perfectley( with a bit of adjusting)
Ade

I guess if I retention the spring leaf on the right it will even out. Both my front springs are new with new shocks so I guess I would only have to do the back.

This I think is something all Datsun owners will experience.

I drive a 1977 1200GX Sedan and have also the same problem.
I have 185/60 R13 wheels all round and have noticed that the driver's side back wheel touches the arch when going through some dips in the road.
What must be remembered is that about 70 to 80% of the time only a driver is in the car. What does that mean? Only the driver's sides springs are carrying most of the load.
So after about 30 years I think they will get a bit "tired" of carrying the weight.

This is not too serious.
The spring leafs must just be removed from the back and retensioned according to specs.This is done by heat treating them and bending them back to get the desired tension.
Remember to replace the rubber bushes aswell while the leafs are off.

well, a cheap option would be to swap rear springs left to right. This way the car might sit flat when driver is installed. Over time you will have 'free' retensioned springs

If you have a company that does springs, then the best option in the long run is to remove the springs & have them reset. This will make them both the same & you can have them lowered at the same time if you want.

Be sure to fit new bushes, urethane ones if you can get them, & replace the shackles if they are worn. A new set of shock absorbers & you won't know yourself. It will feel like a new car.