Two suspensions were used in the 760 lineup - the Multilink, a.k.a. IRS, a.k.a. Independent Rear Suspension, and the Constant Track, a.k.a. Larsson Axle, a.k.a. Live Rear Axle. A subset of these is also referred to on the board, the Nivomat Suspension. Nivomats are special load-leveling shocks (when you put a lot of stuff in the trunk, they 'pump-up' to keep the rear from sagging.) These shocks were used on both types of suspension, and they don't affect anything you're asking about, but FYI, they were standard issue on all 760s.

The early 760s, up to '86 I believe, all had the Constant Track suspension. This is basically the same setup as all the Volvos that came before it - a solid axle connecting the two rear wheels, suspended by coil springs. A bump that hits one wheel causes a reaction at the other wheel - not normally a problem, but in performance terms, you can end up with some instability at the limit of cornering performance on a rough road. Enter a bumpy corner at the limit of the tires' adhesion, hit a bump, and the tail can step out on you. It also means that bumps jiggle the car moreso than with an independant rear.

From '87 on, the 760 sedans switched to the Multilink suspension. The differential is mounted to the body, and the two axles which react independently from each other deliver power to the rear wheels. In so doing, you let each rear wheel operate to the fullest, without interference from the other wheel. Roadholding and ride comfort is improved. The downside? complexity, cost and weight. The Multilink is heavier than the Constant Track, and there are some expensive items (like CV joints) in there that require maintenance. 760 wagons never used the Multilink, as there it would have required raising the load floor.

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Speed Racer, '83 240 R, '74 164 E, '93 940 OL1 (Manchester, CT)