47 cadillac has a panhard bar, anyone know why?

Started hot rodding my 1947 cadillac model 61, just clipped the front suspension and am working on dropping the rear suspension (2" wide leaf springs). The car has a panhard bar. Anyone know why it would have one? I thought leaf springs were able to locate the rear side to side on their own. It is a big car, did they have that much body roll to need one? I will be swapping out the rear and can transfer the brackets if needed, but I do not understand why it would need a panhard bar. Is there something I am missing here?

 

My guess is Cadillac did some develpment work and decided that suspension really needed a panhard bar to control some kind of movement that didn't feel correct.
Did Cadillac make a shackle component or hanger that is prone to flex without an additional lateral support? Or did they just do it to prevent short life span in the bushings at the leaf spring ends?
If you remove the panhard bar, I'm sure it won't take long to figure out why Cadillac built it that way.

 

I wouldnt take it off.

 

If I remember correctly my 49 Sedanette had a panhard bar on the rear. Cadillac was ahead of the game on suspension. They introduced air ride back in 53 I believe. With that big ole body I Imagiine there was quite a bit of roll.

 

It shouldn't be there, not original? Cadillac ran parallel leafs springs in the rear end and not the trailing arm suspension that Oldsmobile ran. Panhard bar is a must with trailing arm suspension as there were no top arms, only lower.

 

I believe you are wrong, a quick search seems to indicate that '47 Cadillacs did indeed come with a panhard bar from the factory despite having leaf springs. Maybe you should check into it.

 

Both my '37 LaSalles have panhard rods from the factory. The shackles are softly bushed and the rod controls resultant slop as the car side loads from cornering force.

 

Cadillac likely used a Panhard bar with leaf springs because they were a premium product and cost wasn't as much an issue as it might have been for Chevrolet, for example.

Even though you can "get away with" no Panhard bar on leaf style does not mean it isn't desirable for optimum suspension control.

Further, I don't think it has to do with body roll nearly so much as it does with lateral location of the axle in turns. Even if there was no roll whatsoever, in an aggressive turn the leaf springs and shackles/bushings would all have "give" that would affect axle placement as mention by La Salle Gearbox above.

Ray

 

I will keep it, just have never seen one before on a leaf sprung rear axle. I just ordered new spring bushings as the originals are shot but the springs are fine. There is enough preload on the panhard that when the car is in the air the panhard bar is actually pulling the rear over to the right side, it centers out when the car is on the ground.

 

Somewhat dinky looking by comparison to ones you see in more modern suspensions, but here's the one on the 41 coupe a friend is rebuilding:

 

"enough preload on the panhard that when the car is in the air the panhard bar is actually pulling the rear over to the right side,"

You'll get that because the rod moves in a long arc as the suspension travels. As Hnstray says above, the panhard rod has nothing to do with limiting body roll. In other words it acts either in compression or tension (and not much of that at all), not in torsion.

If you think about it, the axle also tilts fore and aft (another way to say this is the wheelbase changes, one side longer than the other) when the car leans in a corner. This due to the free end of the shackle moving to accommodate the spring either flattening or bowing up.

 

Holy cow, I'm amazed something that small does anything at all. I guess they probably wanted it to flex rather than bind or break?
With those narrow springs and dainty looking shackles I think it was probably wise insurance to keep the tires from moving enough to rub the fender skirts. I'd keep it if it were my car, too.

 

Hi I have a 41 and a 49 both have Panhard bars...it only about 5/8 solid rod ..it doesn't act as major structural part of the suspension I would have a guess they were to stop body sway or rolling...this would stop motion sickness.....Caddys were a top range car and the last thing you want is the people in the rear vomiting over fellow passengers....Doug

 

I don't see any way that would work as an "anti-roll" or stabilizer shaft. It would only limit the transerve movement of the axle assembly. Did the Cadillacs of this vintage fit the tires that closely to the rear fenders and frame? You can bet that if the engineers saw any indication of a tire rubbing somewhere this would have been the easiiest, most obvious solution. And they wouldn't have had to stiffen up the spring eye bushings and risk losing their quiet, cushy ride!

 

It's not about preventing the tires from rubbing.........it's about limiting the amount of 'steering' of the car by the rear axle movement......as pointed out in an earlier post, even the change in the effective length of the rear springs when the body rolls in a turn, as well the lateral movement mentioned here, both induce steering inputs to the chassis. Any limitation of those inputs improves, however little, the handling and predictablility of the car.

There are some great textbooks on this subject.......if you doubt the physics involved ....check it out for yourself. None of that is to say any car not so equipped is just going to fly off the road at the slightest provocation, just because it lacks these parts........but it does make a measurable difference.

The fact that you CAN get away with not having Panhard cars or Watts Links or a number of other sophisticated devices is why they don't have them. Its saves money and the average dimwit American driver wouldn't be able to detect the difference anyway.

Ray

 

I can't tell you what years, but as others have said, at least some leaf spring Cadillacs had a Panard bar.

As was already pointed out, a Panard bar can do a better job of locating the car laterally then leaf springs, especially when the leaf springs pivot on rubber bushings.

 

This is all very interesting, but I need a picture to explain this, please.

 

The picture in post # 10 should serve to illustrate the principle. Ignore the fact the pandard bar is so 'wimpy' looking....I must admit I am amazed it is so small in diameter. But I digress.

First of all, when the chassis pictured is loaded with the complete body the springs will compress and the panhard bar will (ideally) be level, not angled as pictured.

It's role is the keep the axle centered in the chassis instead of allowing the body to move sideways in a turn due to centrifugal force. That lateral movement of the body/chassis, especially when combined with body/chassis roll, if not prevented, will change the angle of the rear axle from perpendicular to the chassis centerline and induce 'steering' or 'turning' forces into the wheel alignment.

Think of an old farm wagon that pivots the entire front axle to change direction. It's the same principle in automobiles, though in the rear and to a lesser degree, but it's there nonetheless.

The best method to control a live rear axle, so far as I know, is not the Panhard Bar, but a Watts Link. The difference being, as someone already mentioned in an earlier post, the Panhard Bar moves in an arc and does not fully limit sideways movement, but does reduce it considerably. The Watts Link keeps the axle centered no matter how much verticle movement occurs. Watts Link control can be found on the last generation of Ford Crown Vic and Mercury Grand Marquis. Maybe earlier versions too, I am not sure about them.

Ray

 

A parts manual would answer this question, more than likely listed as "rear axle locater" as that is what it does.

 

Stepdown Hudsons ran splayed leaf springs and a panhard bar also...

 

That picture of the 41 is the same setup my 47 has, spindly diameter and all, I agree doesnt seem robust enough to help under hard cornering. The leaf springs are a little narrower than newer stuff (2" vs 2 1/2") but the shackles seem conventional in design. I will keep the bar and transfer the brackets over to the new rear as soon as I can get it out of the donor vehicle.
One other issue is the use of tube shocks, maybe the rear had to be somewhat rigidly located because of the knee action shocks? I will losing them and going to modern tube shocks.

 

Some jeeps had them on the front end WITH parrell leaf springs. I don't think the watts link was invented yet. Lol
MrC

 

thanks hnstray-that helps

 

The ONLY thing a panhard does is locate the axle from side to side, to keep it centered. It does not help with body roll, nor does it help with preventing axle 'steer' caused by body lean around corners. If you look at the picture carefully you would be able to see there is no way for it to control the forward/rearward movement of the axle. ........and the Jeeps that had them were the '87 - '95 Jeep Wranglers (YJ's) which is also when they went from 2" front/2.5" rear springs to 2.5" at both ends, go figure .

 

Relax a bit an reread the post that appears to have you so upset.....nowhere does it say that the Panhard bar controls body roll...the comments say that it locates the axle laterally.....which is important in it's own right...but that that is even more helpful when body roll is present to reduce/prevent steering inputs from axle movements.

btw....I have considerable experience with Jeeps, starting with a '46 CJ2 by coincidence, in the early 70's, and on to later CJ, YJ, MJ, TJ, XJ and WJ and am quite familiar with their suspension set ups.

Ray

 

I'm not worked up, justgiving my opinion. Being you are also familiar with Jeeps and therefor leaf spring suspension, you should be able to figure out that a panhard bar does not can not locate the axle longitudinally. Locating the axle laterally is important to a degree, but will not helpreduce steering inputs from body lean.


Also the jeep reference was not a shot at you , just stating a somewhat puzzling fact.

 

Body roll can be induced by shackles that are too long to control lateral movement. In my opinion, back to the posted pic, the spring shackle doesn't appear to have lateral control like a shorter shackle, or a bridged shackle that has the sides connected or folded during stamping.
IMO, that Cadillac suspension really needs to have that thin panhard bar to keep Cadillac's spring shackles from bending over. Without it, a long sweeping turn will let the vehicle sideforce put a bad driving feeling into the car.
It's a different feeling than having a tight kingpin in a steer axle, that makes a vehicle wag with steering corrections. It would have a similar feeling to having a feeling to go left and right under the seat, while the steering wheel feels ok, like the vehicle wants to swap ends because the rearend can move side to side.
That feeling is very uncomforting when it's in the front end, from which you steer with, and then sometimes worse because the steering wheel doesn't affect what you feel from the seat.
Hope I described correctly. I've worked a lot of years in drivability problems with my hotrod and at work with cars up to semi truck sized stuff and bigger.

 

Your friend needs to rethink this design if the bar pictured is anything but a mock-up. Remember that a panhard bar has to work in both tension and compression. That one has no structural value in compression.

 

I've got a '38 Lasalle rearend at home....with panhard bar.

 

Hnstray has explained the use of a Panhard bar very well. I was an SCCA road racer for years and virtually every racecar with parallel leaf springs also ran a Panhard bar or Watts link. Watts link being the superior application. As Hnstray says, the prime objective is to prevent rear wheel steer.