Interesting, what did you need to make the hydrocompensator work? Doesn't it have a pump and hose getup of some kind? I'd also assume that different (vertical) spring rates were used in the rear end of those cars to allow the compensator to do more of the leveling work and give a different ride.

For posterity's sake I might as well post the rest of Chris' admittedly scary writeup:

"The alignment I am referring to is the angle of the swing axle hinge pin in the vertical plane. Since the pinion shaft and hinge pin are forced to swing in the vertical plane together, a change in the angle of the hinge pin implies an identical change in the angle of the pinion shaft. This angle is changed by sliding the carrier arm either in or out on the rubber carrier bushing's outer sleeve. The further out the carrier arm is away from the axle assembly, the more "up" attitude the hinge pin and pinion shaft will have. The further the carrier arm is in towards the axle assembly, the more "down" attitude the hinge pin and pinion shaft will have.

The ideal situation is when the carrier arm is positioned such that the center line of the hinge pin would pass through the inner end of the radius of the arc that the rear axle trailing arms would move through while the car's suspension is in it's "steady" state (neither compressed or extended.) (This is a fancy way of saying that the center line of the hinge pin is parallel to the center line of the car, assuming that the ride height of the car is correct.)

Think about what has to happen when the rear suspension is compressed or extended. The outer ends of the axle tubes HAVE to swing through the arc dictated by the trailing arms, but the relative height of the hinge pin is held constant (almost). This means that not only are the ends of the axle tubes swinging up and down, but must also swing FORWARD to follow the arc of the trailing arms. In order for the axle tubes to swing forward, the angle of the hinge pin must also change. When the suspension is compressed, the hinge pin is forced to point down in the front. When the suspension is extended, the hinge pin is forced to point up in the front.

The problem comes about when the center line of the hinge pin does not intersect the inner end of the radius of the arc that would be followed by the trailing arms. Said another way, the center line of the hinge pin is not perpendicular to the tangent of the arc. In this case, before the suspension can be extended or compressed, the attitude of the rear axle must be forced to rotate into a position where the centerline of the hinge pin is nearly correct, or the axle tubes will not swing. In other words, the misalignment tries to get the axle tubes to rotate around an axis that does not coincide with the physical axis of the hinge pin. Obviously, the axles tubes are going to rotate only around the true physical axis.

It takes a fair amount of force to "auto-rotate" the rear axle into the correct position for suspension deflection, and this force is created at the expense of ride quality.

The only reason that the suspension continues to work at all under such mis-alignment conditions is because of the rubber parts between all of the rigid parts.

Chris Johnson"

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1967 230S automatic
Boston, MA