Greetings all, My car is a 1961 Ford Country Squire. I have a Fatman front clip with coil over shocks (to accommodate a Coyote Engine), but the rear suspension is stock with new leaf springs. My issue is when going over rolling ups and downs in the road surface; not just bumps, the car bounce up and down "kitty korner." (for lack of a better word) Like the right front goes up at a different rate than the left front and same with the rear. The left rear and right rear don't respond equally either. The front and rear are not in sink. The coil overs are adjusted the same and both are rated 700 lbs. How do I test whether I am correct and how do I fix it? Thanks! Any help is greatly appreciated.
My guess is that things are not as uniformly adjusted as you think they are. The best way to check would be on a set of scales. First thing I would do is loosen the bolts on the leaf springs and re-tighten them while it is sitting on level ground. I assume the coilovers have adjustable damping. Make sure the damping settings are the same. Did you adjust the springs for the same preload? If the side to side weight distribution is off, the preload may need to be different on left vs right.
First off, is the rear leaf spring, or three-link with Panhard bar? If it has a Panhard bar (a horizontal link between the frame and axle housing), it's in the engineering of the bar that causes the rear to 'kick out' in that manner when going over road undulations, as the axle is forced to move in an arc when it moves up and down. I'm guessing that the rear end kicks in only one direction?
If it's hopping sideways, recheck your hardware torque. I'm not the first to miss tightening something to spec. Ensure the axle housing is properly seated to the spring pack, and the top plate is correctly centered. Finally, inspect the attachment points on the frame, make sure there's no cracking.
