[Mark66]

I am trying to determine the center of gravity (NOT the center of gravity height) for my 1966 4 door Bonneville and Grand Prix so that I can safely use a 2 post symmetrical lift. Although the 1966 Pontiac Chassis Shop Manual clearly identifies the proper location for the lifting points on the cars, it appears to be silent as to the location of the center of gravity (or maybe I can’t find it). As the lift arms allow for quite a bit of horizontal travel when initially locating them under the car, I need to know where the center of gravity of the car is so that it can be properly aligned with the center of the lifting posts.
I have seen some on-line center of gravity calculators that I may use if I have no other choice – in the past I would simply my head with the center of the lifting post while sitting in the car. But as I get older and more safety conscious I wonder if this is correct. Maybe there was an obscure Pontiac Service News Flash or Craftsman News issue that covered this but I have not seen it.
So what is the best way to determine the location of the center of gravity on 1966 Big Pontiacs?

[Keith Seymore]

You can get four corner weights and do the math - or - just take two floor jacks (one on each side) and pick the car up off the floor, moving the jacks slightly fore/aft until the car balances.

That's how we did it 60 years ago, only back then we used scissor jacks.

K

[rustedgoat]

It's between the bow and stern. I'm starting to love those big cruisers.

[Mark66]

Keith:

You suggestion would certainly give the correct results. My only concern i using your approach is the possible effect on a frame that is 54 years old and the risk that I might bend the frame just enough that the doors no longer close. Perhaps by putting long, narrow steel plates between the scissor jacks and the frame I could spread the pressure enough to avoid the risk of bending the frame.

But thanks for the idea.

[Scarebird]

If the car is running, go to a State Patrol or other axle scale, weigh, and do the math.

[barrierblue66]

Mark66,

Have had my '66 GP up on my 2 post lift many times over the last 5 years. To initially find my center, I lifted just enough to clear the tires from the floor, and used a level across the lift arms. Once I had a good, level reading, I marked the floor for this car, which is different than the position of my '63 Cat Safari.

1963 Catalina Safari
1966 Grand Prix