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Tech Question

john shoe, Murrieta, CA, 1975 dodge dart sport 360

Rick- I’ve not so much of a question , as much as rhetoric;an inquiry about Chrysler’s excellent (in my opinion ) rear suspension /drivetrain from the golden years (1989 & earlier ) of rear wheel drive.I’ve seen and heard too many times in the last 2-3 years where someone –typically a customiser — will replace the superb leafspring /forward-of-centre axle mounting suspension , in favour of a 4 link setup ; Iwon’t delve into the whole rack & pinion butchery of the front end … WhatI’m after here is your expert opinion regarding the OEM rear suspension vs.the neuveaux multi-link / 4 link rear suspension systems. I’d truly like tosee your opine in print , as you’ve presented some excellent articles onfront end mods (which I’ll be applying to my ’75 360 Dart Sport really soonhere … ). It seems like about 15 – 20 years since you’ve tech’d a rearsuspension dial-in (or I’ve just been that much out of the loop!). Thankyou much for your time and all due consideration! Sincerely, Shoe


The 4-link rear suspension swap isn’t nearly as bad as the tubular K-member/ coil spring front deal. The key is that it has gotta be done right, andproperly attached to the chassis, and some kind of lateral location systeminstalled, preferably a Watts link, or, at least, a Panhard rod.

With the modern CAD programs, a skilled user (and fabricator) could probablywhip up something good. However, generally, the unsprung weight savings, ifany, are small, and the geometry improvement also small if done right; ifdone wrong there can be significant rear-steer problems. At that point,however, I think I’d start thinking about a sea change: IRS.

If lightweight fiberglass or composite leafs could be found with 100,000 miledurability and a reliable front attachment system that could handle highaxle torque, that would sure be the way to go.

One’s thing’s sure: The Chrysler asymmetrical rear leaf suspension was a lotmore sophisticated than it appeared at first blush. Dialing it in is prettysimple, a condensed version:
(1) Get the spring rate where it needs to be for your application.
(2) control windup without binding (quadrashocks, or, perhaps, Cal-Tracks).
(3) Be sure the spring is nearly straight (“flat”) at rest, decamber as required.
(4) Add adequate damping.



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