47 cadillac has a panhard bar, anyone know why?

Why even Ford went to untensioned springs, thick rubber shackle bushings and Panhard rods both front and rear in 1942-48 in order to compete with the rides of competitors, so why wouldn't Caddy do it stay up top?

 

Hi .. Mossback44..This is factory ... its 5/8 solid rod .threaded at each end for adjustment...I have 2 Caddys 41 & 49 and both off them are fitted with it........

 

Although the panhard bar/rod or track bar is used as a lateral locating device, it also stabilizes and maintains a roll center. The Cadilliacs open driveline combined with the narrow leaf springs, allows lateral movement, a panhard bar keeps these changes in geometry in check through rear suspension travel/roll.

Usually the leaf spring alone is used to locate the axle in all three dimensions. Fore/Aft; Side/side; UP/Down. But even then the spring will bow, the bushings will compress and the axle will move about. The panhard prevents the unwanted lateral movement. Possibly, by using the springs as just a fore/aft location device, the spring itself could be made less stiff allowing a lower spring rate for better comfort while not sacrificing stability. It is a Cadillac. As for reducing rear steer, the leaf spring will compress and lengthen, combined with roll, and the fact that the leaf spring is a suspension link that travels in an arc, there will always be some rear steer induced.

We could argue that the Watts link is a far more accurate device in keeping the rear axle laterally located and the roll center, centered. The complexity of the Watts, the real estate it takes up, and the added weight on a chassis can quickly show diminishing returns on a production vehicle. A correctly installed Panhard that is long as possible will do a sufficient job of keeping the rear stabilized.

 

Correct, but full size Cherokees and Grand Wagoneers had them as well...both fore and aft in some years. If you drive two full size Jeeps, one with bars and one without, you'll quickly understand their value.

 

No, it does not locate the axle longitudinally.

But...in terms of lateral location an axle located only by leafsprings is dependent on the stiffness of a lot of stuff - the front spring-eye bushings, the rigidity of the axle-to-spring mounting, and the springs themselves. Not so much the rear shackles. A rear axle located only by the springs may move as much as two inches either direction under high cornering loads...and so it's not a rear ROLL steer effect but there's definitely DEFLECTION steer from the side-loading on the rear suspension.

A Panhard moves in an arc; the longer the link the less lateral displacement the arm creates. A Panhard on a leaf rearend fights the springs for control of the axle somewhat, but as long as the spring bushings are soft enough and the Panhard is long enough it all works fine.

 

From Wikipedia:

"Watt's linkage (also known as the parallel linkage) is a type of mechanical linkage invented by James Watt (19 January 1736 – 25 August 1819) in which the central moving point of the linkage is constrained to travel on an approximation to a straight line"

Original application, making the upper part of a steam-engine connecting rod go straight up and down. Probably the only part of the modern passenger car not invented by Frederic Lanchester

 

My dads 68 imperial had one as well, its a lot later, but i wonder if the earlier imps had it as well. Now you guys have me thinking about adding one to my plymouth.... Im already going to be adding a rear sway bar, why not a panhard bar too!

 

Bringing this back from the dead just to update in case anyone runs into this thread in the future. Looks like the original posted pics are gone so I posted some. I ended up removing the panhard bar, rebuilt the leaf springs with new bushings, installed 2" lowering blocks, and replaced the knee type shocks with tube shocks angled to the center of the car. The car drives great, corners with no issues and handles damn good for such a big boat.
This is the original setup



new setup





I planned on putting a bar back on if it was needed but turned out fine without it. Maybe the modern shocks are helping offset any movement that was there with the original setup?

 

If it drives well enough to suit you, I have no quarrel with that. However, the tube shocks may be an improvement over the lever style, but they CANNOT have any significant effect, if indeed any effect at all, on lateral axle placement. The shocks are free to shorten/lengthen with relative ease and more important, the top and bottom eyes easily pivot.

Again, if you are happy, I am happy. But. as said from the outset, a Panhard bar was not absolutely necessary in a parallel leaf spring setup, but probably offered some tangible benefit.

Looks like you have made a lot of progress if you are out driving the Caddy.
Congratulations........wish I were that far along on some of my projects.

Regards,
Ray

 

I figured the shocks were too soft to do anything as far as stopping the movement, but thats ok, drives great. I think I put close to 4000 miles on it last year, will be out again in April or as soon as the snow melts.