[Joe's Garage]

We haven't put them on a GP, but most 1970-72 GTOs with old, tired springs will go up about 1-1.5" at the bumper, even without any extra load.

It just depends on how worn-out your original springs are.

Height is only one part of the equation. Grand Prixs were designed to ride smooth, and some of them had the factory air-shock system to keep them level. THOSE have really soft rear springs and used the shocks to compensate for it. And they ride really smooth.

The other part of the equation is SPRING RATE, or how much weight it takes to compress the spring a certain amount - I think it is 1".

Here are your three choices:

5385 wire diameter = 0.59"
6319 wire diameter = 0.53"
CC501 wire diameter = 0.61"

Thicker spring wire is harder to compress, thinner is easier.

The Grand Prix is heavier than the GTO, so it kinda makes sense that the factory GP rear springs would be slightly thicker than a factory GTO rear spring. And it also makes sense that the Cargo Coil 'CC' springs would be even thicker.

If you can find someone with an older MOOG catalog, from the late 80s or early 90s, they used to have a specification section with spring rates and anticipated load for each part number, along with the free and installed heights.

When I was working the parts counter at my local speed shop, we could use all those specifications to calculate how much higher or lower the car would sit with various springs.

We used to install a lot of LeMans station wagon rear springs into GTOs back-in-the-day. As I recall, the back end came up about 2" and the ride firmed up.

Good luck!