Just a little update for my racing friends on something several of us have been working on this off season. Many of us that are trying to race our older muscle cars have had issues getting our triangulated four link rear suspensions to do something they weren't ever really designed to do...keep both rear tires planted when cornering hard. I have tried many band aids on Barney which all have helped a little, but none really solved the issue completely so I decided it was priority number one this off season. I'm tired of my rear wheel drive car lifting the inside rear tire in the air on corner entry.
My first thought was to put a Watts link on the car to lower the rear roll center. The issue is with the lowered ride height, the very short upper control arms are at an extreme angle and this puts the roll center somewhere up around 18" high or so. A Watts link (or Panhard bar) is sometimes used to lower that roll center to a fixed height but what we found is that the axle housing also migrates left and right while the axle is articulating and if you try to hold the roll center in a fixed position, it puts the rear suspension in a bind.
I first discovered this by doing a little demonstration on my rear axle which you will see in this video. The shocks, springs, and sway bar were disconnected, the axle is held at ride height with a jack and articulated to simulate body roll. You can see the axle migrates over a half inch each direction...no good...and the roll center is somewhere up around the trunk floor and it moves around as the axle articulates. Right after I did that I saw that Scott Wheeler posted pictures of his newly installed rear axle in his bare A body frame and he also had a Watts link frame in place, so I contacted him and asked him to do some additional testing for us with a camera running. I had him disconnect his springs, set his axle at ride height and articulate the housing under several scenarios. What we found was the Watts link bell crank had to be near the very top of the frame in order for the axle to articulate without bind. The idea behind adding a Watts is to not only lower and fix the rear roll center, but to also be able to adjust the roll center quickly to track conditions. This shows us that we just can't get the rear roll center where we want it without creating a bind given the constraints of a triangulated four link. We even took it one step further and disconnected the driver side upper arm to create a"Poor mans 3 link" to show that movement as well. Huge shout out and thanks to Scott for helping with this, the videos really help to show exactly what is going on. Also thanks to Aaron, Ramey Andrew and Ron for contributing to this discussion and helping to find a cure.
Hopefully this visual demonstration will show others that are trying to help their four link suspensions work better what is going on under there...and help them find a solution as well.
We are working on a new plan for Barney which will be revealed soon but we now know this...it will no longer be a four link setup for sure.