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Chrysler Torsion Bar Suspensions (and Leaf Springs)

The torsion bar suspensions were used across the entire Chrysler Corporation lineup for decades, from Valiant to Imperial, after being originally devised (in Chrysler’s form) by engineer Bob Batchelor; torsion bars were also used in European cars and the Cadillac Eldorado / Oldsmobile Toronado. One thing that made Chrysler’s implementation unusual — other than its universal use — was the use of rear leaf springs with the front torsion bars, instead of rear coil springs. Though the main reason for using rear leaf-springs was most likely cost, Chrysler could boast of some advantages.

torsion bars

The torsion bar front springs used a high proportion of chromium in their steel (though snapping was still not as infrequent as it could have been). The anti-sway bar resisted lean in turns, with various degrees of success depending on its thickness and the suspension tuning. Shock absorbers limited suspension oscillations. Diagonally mounted steel struts reinforced and positioned the front-wheel lower control arms. Widely spaced, off-center mounted rear springs cut acceleration squat and also resisted brake dive.

The angled upper control arms resisted brake dive; and in newer versions of the torsion-bar suspension (used in the 1970s and later) the upper control arm had a front pivot higher than its rear pivot instead of at equal height so that weight would shift forward when the brakes were applied, counteracting the extra weight caused by braking and helping to keep the car level. Likewise, the rear leaf springs were off center, with the rear axle mounted on the thick forward sections of the springs instead of on the centers, so that the stiffer forward sections of the springs would support the body during acceleration and braking shifts. The long, flexible portions behind the axle benefited the ride.

axle

The rear leaf springs were fastened at two points to the understructure for stability, while coil springs mounted in a single place and required stabilizing bars or links. The wide spacing of the leaf springs also helped stability. More to the point, the leaf springs cushioned driving and braking shocks, resisting dive without firm tuning. They also were better at adjusting to varying loads, at least when using multileaf setups (there were monoleaf springs on some base models). The lighter loads were handled by the long, flexible leaves, and heavier loads by the short, stronger leaves. This essentially provided a substitute for the now-common variable spring rates.

leaf springs

“Dana44” wrote:

Leaf springs may be old school, but they are superior to coil springs in the rear. Another trick with the leaf springs is to angle them. If the front eyelet attachments are two inches (one inch each) closer together in the front, and the rear eyelet remains stock, the torional twist of the offset which improves handling. For example, if the front eyelets are 58 inches between the two front eyelets, the rear are 60 inches between the two eyelets, not only do the springs now flex up and down, but they also twist a little bit when they go up and down, which improves cornering.

Coils take up less room, give ability to lower car and drop center of gravity lower, less engineering required for the package, and ability to move rear wheels farther to the rear corner of the vehicle. Additionally, the MacPherson strut design adds coil spring and shock together to eliminate parts, but to get them to handle as well as leaf springs, the ride gets rough, so it is a tradeoff.

Tannon Weber pointed out:

Unsprung weight is a disadvantage, and with the leaf springs, the axle is unsprung. There were vehicles with coil springs in the back that had traditional live axles, like several mid-sized GMs. You have to go true independent to reduce unsprung weight.

Some companies like Alfa Romeo who really get away from unsprung weight — there were models where the brakes were up against the differential before the CV shafts, so that there was even less weight at the hubs.

I like leaf springs and live axles for load (though Dodge is demonstrating that a decent truck can be built with coils back there), but there is an advantage in a driveline where one doesn't have to work with pinion angles and other driveshaft geometry because the differential is attached at the body. But, doing maintenance is a lot harder too, as changing out shocks is hard.

torsion barsThe front end of the torsion bar connected to the front wheel’s lower control arm; the rear end of the torsion bar was anchored in the sub frame so the bar could not turn. When the front wheel rose over a bump, the lower control arm pivoted around the points where the torsion bar was mounted, twisting the bar. The chrome steel in the bar resisted the twist, holding the wheel on the road.

One advantage of the system used by Mopar tuners through the years has been the ability to easily raise or lower the front end of the car by adjusting the torsion bars; with coil springs, the springs must be replaced. Likewise, if the car sagged with age, the torsion bar on that end could be replaced while a spring would be shimmed or replaced.

The related Torsion-Quiet system described rubber cushions which isolated the subframe and leaf springs, reducing vibration and noise the same way that rubber engine mounts do. The problem, though, is that as isolation was added, stiffness was necessarily and by definition reduced, so that cornering was degraded.

torsion-quiet

For decades, using torsion bars rather than the systems used by GM and Ford on most of their vehicles helped Chrysler to have a smoother ride with better cornering than they would have with a more conventional (given the times and costs) system. Through the years, Chrysler vehicles tended to corner better than their domestic counterparts - or felt better. The company eventually went to other designs, when their cars were downsized, and the advantages of torsion bars were outweighed by the disadvantages - a clear and unavoidable tradeoff between noise, vibration, and harshness on one hand, and cornering capabilities on the other. The more isolation was added, the worse the cornering would be.

Here’s a color cutaway showing some of these components:

1975 Chrysler drawing

This is how it fit in with Unibody:

unibody

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