Tech Question - Panhard Bar

Sir,

I question the use or need for a panhard bar on the rear axle of a parallel leaf sprung chassis.

The application is a 1925 Ford TT, a truck with a full box over a new purpose built chassis total weighing close to 4200 Lbs. The shop that built the chassis insists the panhard bar is necessary, I suggest that the two parallel leaf springs should be sufficient to locate the axle and that what is needed is a rear sway bar to add some control and stabilize the chassis down the road.

The bracket (on chassis) failed recently and the truck handled in a very loose manner, the repair to the panhard bar returned the truck to a better managed ride.
It could be that over the two years on the road with the panhard bar constantly pulling and pushing the axle the spring shackles have loosened up giving the added looseness when the panhard bar failed. The panhard bar is long, from chassis across to almost the opposite side on the axle.

In closing, I would add the following to help perhaps with your answer, the springs, when loaded are almost straight front to rear, no arch and the leaf springs are approx. 2" wide with enough leaves to support the truck.

Thanks for whatever thoughts you have on the subject, I drove a 1940 ford Tudor for 18 years with parallel rear leaf suspension, the rear swaybar proved to be the one element that earned its keep every one of those days. I didn't seem to need a Panhard bar.

Cheers, Lesseps

Lesseps,

Wonderful question. Let's see how well I can answer it.

I would stick with the panhard bar over a sway bar any day. As you have found out already, without the bar the truck gets squirrelly. While the springs will keep the axle in place, it does not stop the side to side movement. The bar does. Unless there is a good reason why the panhard bar goes all the way across the truck, I would have it go from the frame to the pig.

Sway bars do as they are called, reduce sway. They do not tie the body to the rear end like the panhard bar does.

I had the bracket on our '47 break and we readjusted it with the truck at curb height and have had no trouble since. I believe setting it up while on the hoist caused a bind. When the bracket broke I knew right away there was a problem for the handling went way south.

Panhard and Sway Bar? I would not go with both, do one or the other only.

As for the springs being flat, as long as the truck sits well and rides well the position of the springs does not matter. Springs do not care if they are smiling or frowning.

-Mike