1973-77 rear springs
 

Does anyone know if '68-'72 rear springs are the same as the '73-'77 rear springs? I'm looking to put a set of Moroso trick springs on the back of my '76 Grand Prix and I'm not sure if they are the same.
Thanks in advance.

Not the same
 

As far as I know, they're not the same. Get a pair from Summit Racing or Ames Performance from their catalog. Better yet call them and they'll ensure you get the right one.

They are not the same, if you are just trying to raise the rear end a bit, I used to put same year El camino Springs in, I tried A-Body Station Wagon Springs once, but they were a little to Stiff of a ride. But the 73-77 El camico springs always worked on my 75-77 GP's.

74-77 should be the same, the 73 springs are a bit lighter as they did not have the 5mph bumpers on the back yet.

I thought that they would be different. Some websites list rear springs as fitting '67-'77 A-Body cars while others split it up from '68-'72 and '73-'77 respectively. I'm not really looking to change the ride height. I wanted to use Moroso trick springs on the rear, but they don't make them for these cars. I'm going to get rear springs from Belltech and going to look into an airbag to help compensate for flex on the right rear spring to try and even out the starting line launch. I hope all that makes sense. :)

On a side note, if you're looking for another source for springs that will fit our 73-77 A-body, the '94-'96 Impala-SS springs are a direct fit. I installed a Hotchkiss kit on my Can Am at all 4 corners in 2018 intended for the Impala-SS and they were a direct bolt-in.

That's definitely good information. So the spring rate is the same between a mid 70's A-body and an early 90's B-body?

That makes sense as I was told years ago by a GM Chassis designer that the 77-95 B-Body Chassi was based off of the 73-77 A-Body Chassis. I know for a fact that front Sway bars and front spindles swap between them.
never thought about rear springs though.

I never said anything about spring rate. I said they were a bolt in. The spring kit I purchased lowered the car about 1-1/2" from where it was with the original springs. Ride quality is tighter than it was but not harsh like a tuned F-body.

I understand other parts are interchangeable as well, such as the steering gearbox. Apparently those 90's B-body frames were just about identical to the '73-'77 A-body frames.

Steering boxes from 1985-1996 Caprice police or Impala SS are a huge upgrade over the original 1970's variable ratio, zero road feel boxes. The Caprice hydraulic fittings are o-ring, but Lee MFG. sells adapters, and the input shaft spline count is different for 1973-76 A bodies, but a direct fit for 1977 A bodies. You will need a different rag joint for those earlier A bodies.