Is a Swing Axle or IRS Better?

Swing Axle Pluses

(Through '68 they used swing axle rear suspension)

The swing-axle suspension offers lower unstrung weight, which is the weight that "bounces" with the wheel.  This lets the tires follow road surface more closely.  This results in less inertia for the shock absorbers to overcome.

The swing-axle suspension also has fewer parts.  Fewer parts mean fewer parts to break.  There's an economic consideration too.  The swing-axle suspension generally costs less because of the old rule of supply and demand.  More are available.

Swing Axle Minuses

Swing axles pivot only at the gearbox. The swing- axle is 'fixed' at the wheel (that is, it is not able to flex up or down), but is able to move up and down at the transmission end. It required the rear wheels to move in an arc, rather than vertically, when hitting bumps. in some cars (beetles and corvairs and some early porsches), it could cause the wheel to tuck under the car during high speed cornering.

The swing-axle suffers from excessive camber change.  To restrict positive camber at full rebound special spring plate stops are needed to limit rebound travel. 

The IRS

(Independent Rear Suspension. A form of rear suspension that allows the rear wheels to move vertically up and down, independently of each other, to compensate for bumps and road surfaces. uses a double-jointed rear axle, with cv-joints at each end. )  From '69 on, they used IRS

If you could ask a suspension engineer, he'd tell you the IRS, or semi-trailing arm rear suspension, is the better.  The IRS can be modified for ground clearance and wheel travel without the extreme camber change of the swing-axle. 

IRS Minuses

The IRS suspension has its drawbacks.  Because the system has more parts to wear out or fail.

wear out or fail