Panhard Rod on a Leaf Spring Car

[firebob]

It seems like a panhard bar is a must on a rear coil spring car but I'm wondering how important it is on a leaf spring car. I spent the last two days trying to install tailpipes on my first gen working around the brackets and braces. I got it done but it wasn't easy and it got me to thinking how much it's really needed on a car with leaf springs.

Robert

[David Pozzi]

I would just put Del-A-Lum bushings in the top position of the shackles. This will stabilize the shackles and prevent them from deflecting side to side. If you do feel the need to use a Panhard bar with leaf springs, mount the Panhard so it's roll center matches the leaf spring roll center or you will have bind in roll and oversteer.
David

[DartorDemon]

I may be a bit of a suspension newb, but it seems totally unnecessary to me. Its function is to keep the rear axle centered, but the axle is directly bolted to leaf springs that have 4 anchor(mounting) points. So how much could the axle shift?

[neki67]

So how much could the axle shift?

More than you would think/like. At least as long as you have rubber bushings. Minimalized with Del-A-lum or the likes. I'm using a Watts Link, the rear is soooo much more stable. Even cornercarvers.com supports that!

In all honesty; I'm using composite springs, steel is probably less instable.

[exwestracer]

More than you would think/like. At least as long as you have rubber bushings. Minimalized with Del-A-lum or the likes. I'm using a Watts Link, the rear is soooo much more stable. Even cornercarvers.com supports that!

In all honesty; I'm using composite springs, steel is probably less instable.


Dave Pozzi is absolutely right. The panhard bar forces the rear axle into an arc, and this needs to be matched to the natural motion of the leaf springs as closely as possible. The Watts is a much better choice on a leaf car, but probably won't help with the OPs exhaust clerance issues...

If you do use a panhard or Watts with a leaf car, I would NOT install stiff bushings in the springs. Let the linkage do the work.

[silver69camaro]

Before I did anything I would actually measure how much the axle is deflecting laterally. The only time I would seriously consider it is with composite springs.

[exwestracer]

Before I did anything I would actually measure how much the axle is deflecting laterally. The only time I would seriously consider it is with composite springs.

(Better yet...)

[ace_xp2]

There were some Trans Am cars which ran a wider rear shackle so the bushing could slide left to right. That way the panhard would serve as the sole lateral locator. Being able to adjust roll center can be a big advantage, but I don't see any adjustment there, so it's hard to say whether or not the new couple defined by the bar would be an advantage over the one defined by the leafs. The total reduction in lateral deflection really depends on the stock spring design, the wider the leaf the less the change.
Add.: It's already on there, why not take it out and see how it feels with and without? It's only two bolts.

[firebob]

A couple of things...I should have shown a pic of the other landing point so you could see the swing is centered as well as it could be given the confines of spring travel. I should've also included that I'm running slide-a-links with the solid alum/delrin front spring eye bushing and the rear shackles are all urethane. The only place there's any rubber is in the ends of the panhard bar. An adjustable bar would've been a better idea but this one was free and it was mounted so that with the suspension fully loaded there is no lateral pressure right or left. The rear exhibits very little movement and I have to try very hard to overdrive the rear of the car. I wouldn't think that the leafs would let the rear end move too far in stock suspension form and even less in it's current configuration. I just got to thinking if/how much it was totally needed on a car with leaf springs. I'll try to post a pic of the other mounting point tomorrow.

[jknight16]

With my non-factory multi-leaf rear suspension, before the composite springs and watt's link, I felt some disconcerting movement in the rear of the car through higher-speed canyon turns that I attributed to the rear end moving. Now with the watt's all of the surprise rear end activity has been eliminated.

[firebob]

So I got under and measured up from the floor to the pivot points on both ends of the bar. There's only 1" difference, so in a 50" radius arc that one inch isn't going to give the rear much sideways movement especially with rubber bushings in the ends. The springs will only go 2 1/4" at full compression and it's never going to go that far anyways. The only real movement caused might come when the rearend springs unload. I had the body on jackstands and the rear springs totally unloaded with one pivot bolt out and it move about 3/4" inboard. Nothing to be concerned about to my mind.

But back to the original question...Is it really needed in a leaf spring car? Or is it just overkill and extra weight?

Robert

[High Plains Mopars]

But back to the original question...Is it really needed in a leaf spring car? Or is it just overkill and extra weight?

Robert

Are they really needed, no. Can they improve things, yes, depending on what you're doing with the car, how much power your putting down, and your driving style. I know for certain that the Plymouth and Dodge trans am cars of the 1970 seaons used panhard bars with their leaf spring suspensions and they managed to qualify at the front of the pack several times. I'd imagine other cars had them too, but I'm not familiar with who may have used them.

Provided you freed up the leafs to only act like springs and they are not binding againts the motion of the panhard, and it is built to be adjustable, you can use it to alter the rear roll center location which can have a big influence on corner exit bite.

Since it sounds like you simply placed in a spot to best accomodate all of your exiting hardware without considerations of impact to roll center location and I didn't see any mention of adding leaf spring pivots or other methods of freeing up the leafs to pivot, odds are it will not be as beneficial as possible and is adding extra weight.

[firebob]

HPM,
It's true that it was installed in a static position with basically no way to fine tune or adjust/change the stock roll center of the car. I'm not quite sure what you mean by allowing the spring to "pivot". I don't believe the addition of the bar hampers or limits the normal operation of the springs other than not allowing them to move sideways in relation to the body. Since everything has already been worked around in it's present configuration I'll most likely leave it in unless I become convinced that it is detrimental to the performance somehow.

Robert

[High Plains Mopars]

There is the possibility of binding occuring within the motion difference bewtween leaf movement and panhard movement. If you are only moving an inch or two, you may never run in to this binding. However, it does occur in some applications because of the travel involved and physical location adn size of components. Some racing leaf manufacturers offer a pivot mount for use with leafs that utilize alternate locating devices to allow the leaf to pivot and avoid this bind. The upside to using a pivot is that if you have competing arcs with the locating device, then they will not bind. Downside is you loose the natural roll resistance provided be a leaf that is being twisted by body roll.

Good info on panhards is here, they also have a nice tech note on leaf springs too. http://www.afcoracing.com/tech_pages/panhard.shtml

[firebob]

Just reading an article like that is difficult for me to decifer without seeing an actual mockup and the effect that the different senarios create but portions of it sink in. It seemed like most of the panhard information was directed to coil spring applications but I suppose, to a degree, the effects would crossover to leaf cars as well. It would seem to me that the panhard rod will remove a majority of the twisting of the leaf springs by keeping the body in the same location in relation to the rear end placing most of the sideways pressure onto the spring eyes. It's all a bit non consequencial in my case becuse it is mounted on the only place it can be without a complete change to design. So as it sits, either it performs better in it's present form with it on or it comes off. It feels more planted the way it is to me so I'll keep it till something changes my mind or something better comes my way.

Robert

[exwestracer]

With very little arch in the spring packs (typical of first gens) you aren't going to get that much spring flex anyway. Mostly it would be bushing squirm. Hey, if it gets you to put the hammer down earlier, then it's working!

[Brads70]

I just bought a pair of Hyperco composite leaf springs and was talking with Hyperco about them. They said no real need for a panhard bar, even with autocrossing. With high speeds like circle track racing yes. I also asked about spherical bearings up front and they again said not nessesary. Also asked about higher HP engines, they said no problem, and that they know of a few people that use them in 800hp+ drag racing?
I have all the stuff to build a panhard bar and make my own spherical bushings so I'm going to proceed with that plan.
Just thought I'd share what Hyperco had to say....