panhard bar

[Norm Peterson]

Bushing stiffness or the use of rod ends in a PHB with leaf springs is tied (inversely) to how stiff things like leaf spring bushings, shackles, and the springs themselves are in the lateral direction. As the spring/shackle/spring bushing assembly gets stiffer, the PHB bushings need to be made softer and/or the PHB RCH needs to more closely match the leaf spring RCH. The other side of that coin is that if the spring/shackle/spring bushing arrangement is soft, the PHB can be made more rigid and the PHB height can then be used to alter the RC height.

If you're just adding a PHB to limit gross lateral movement under extreme lateral conditions to eliminate interference and don't wish to tinker with the spring and its mounting, poly or rubber bushings will suffice. 3rd & 4th gen F-bodies use rubber as OE PHB bushings, and it works just fine even with the rubber-bushed LCAs that provide very little in the way of lateral 'help'.

But if you want to use the PHB as a means of altering the rear RCH, the PHB ends need to be at least poly-level stiff, and some lateral stiffness will need to be dialed out of the spring and its related mounting pieces.




Norm

[High Plains Mopars]

It is scaping the door handles in corners when I race it right now. I dont even have sway bars.

I'm suprised no one has keyed in on this quote. No sway bars, scraping door handles, I think this should be identified as the first place to look for improving lateral accelleration before even considering revamping the rear suspension system.

.99 torsion bars, a 1.125 front sway bar, 130# rear springs, .875 rear sway bar, and adjustable shocks and your Dart will entirely change its personality without the need for any special fabrication. Then you can spend you time dialing in the shock settings instead of cutting and welding.

I'd also say you need to take time to understand your roll centers and how changes can impact them. If you don't have it already, Mopars Oval Track Chassis book is a must have. I'd also recommend picking up Mike Martins book on mopar handling. It has been sold under a few different title such as Super Street Mopars, Performance Handling for Mopars, Mopar Autocrossing, etc. Also visit Steve Smith Publishing and pick up Building the Late Model Sportmans car. Very informative about the interrelationship of suspension points and changes.

Once you get that dialed in and feel you need more adjustability to your suspension, then entertain the idea of adding a panhard bar. Honestly the PB is only going to allow you to adjust roll center height and gain rear bite on corner exit. Until you have your car and engine combo dialed in, the extra adjustment of the bar is only going to make life more difficult, not to mention it may change your autocross classification which could put you into a catagory going against much better built and prepared cars.

If you run at a variety of tracks and conditions and feel the bar will give you the adjustability to be fast at multiple locations, then take some time to examine the 1970 AAR Cuda fielded by Chrysler back in the day. They used leafs with a panhard bar with great success. They used a pivot on the front leaf spring mount and a bronze bushing slider in the shackle. Afco still makes a leaf spring pivot for this type of application http://www.secureperformanceorder.co...&ProductID=964. The rear bronze bushing allows some lateral movement of the leafs during p-bar travel to avoid binding. You want the leafs to only act as springs and fore/aft locating device with the panhard bar as the lateral locating device.

I'd say its safe to say that if the AAR team had resolved their engine issues, they would have been a front running team with this set up. Conversely, the Dodge TA team used a watts link arrangment and they never really had their car dialed in like the AAR crew did. By the last race of the season they had ditched it in favor of the panhard arrangment and did much better.

Just my $.02 worth.

[Brad74]

So if I use flex-a-form composite monoleafs with poly bushings, what bushing material and height would be reccomended for the panhard bar?

[Norm Peterson]

Assuming little or no arch under static load, I'd treat the PHB only slightly differently than I would if the springs were steel. Rubber-bushed in at least one end, and mounted within about an inch of axle centerline height. And horizontal with half a tank of gas plus at least the driver's weight simulated.

By the time you've made a leaf spring strong enough in the weak direction of the cross section to hold up one corner of the car and stiff enough to give you the rate in that direction that you want, you've also made it pretty rigid against bending in its strong direction. So the fact that it's composite doesn't buy you as much more lateral flexibility as you might expect. Two to four times that of a steel spring, perhaps, as opposed to the ~10 times that a comparison that considers only the modulus of elasticity material property might suggest. That's probably enough to let you use poly in one end of the PHB, but not both.


Norm

[Brad74]

Thanks for the great info Norm. I thought a composite monoleaf has more lateral rigidity than steel multileafs. Especially multileafs that are not clamped tightly with more than one clamp.

Brad