Thread: "dead spring perch"

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okay guys

I'm new to building cars, this being my first one and being only 19. my question is what is a "dead spring perch"?? i know i need one however i already have a front panhard bar, and i understand the concept of why i need one. I just wanna know what does one look like and how does it counteract the bouncing affect??

any help would be greatly appreciated

I don't have a picture of one to post, but here is the concept. A traditional Ford front spring is hung on both ends by shackles that are free to move as the car bounces. If you build in the normal 45 degree, or thereabouts, angle to them, they do a pretty good job of keeping the axle from moving from side to side from road forces.

But, especially if you install cross steering where the steering drag link moves from side to side, everytime you turn the wheel you are pushing and pulling the axle sideways. To counteract this, you can either use a panhard bar to limit the movement, or turn the spring into a panhard bar (sort of) by taking one of those moveable shackles and replacing it with a dead perch that won't move. In effect, the spring keeps the axle located because this dead perch is ridged.

Never used one myself, as I have never used cross steering, but I have seen them. Hope this explanation is clear and accurate.


Don


PS: It does nothing to counteract bouncing, just side to side movement.

You don't want both a dead perch and a panhard bar. Use one or the other. The dead perch is less cluttered.

Whoever told you that you need it in addition to the panhard bar is out to lunch.

There's an explanation here.

http://www.sachserodshop.com/pdf/15.pdf

The dead perch has nothing to do with bouncing. That's the job of the shock absorber.

haha no i know you don't need both, i ment that i'm going to be using a panhard bar. I just want to know more about the dead spring perch just so i'm aware of it

thanks for the help guys

thought just occured to me, this required even if your running a suicide front end?? just thinking back at other cars that i have looked at and don't remember ever seeing this setup

A car with a suicide front end usually has "side steering" rather than "cross steering". A dead perch or a panhard rod won't do anything for a suicide front end car. Even if the shackles do change angles when you go around a corner, the effect on the handling is hardly noticeable.

Suicide front ends can have different problems that can't be fixed with a dead perch or a panhard bar.

Hot Rod Roy---I believe you are incorrect. A car with a suicide perch on a transverse leaf spring is no different from a geometry point of view than a car with a transverse leaf spring mounted under the front crossmember. Both will suffer equaly from "shackle rock" where the weight of the car has a tendency to swing back and forth on the spring shackles. Both systems will benefit equally from a Panhard rod, or from a dead perch spring mount.

Brian, I appreciate your comments. I was really trying to make a comparison between cross-steering and side-steering.

Let's think about what happens with a cross-steer front end when you get "shackle rock". For instance, when you turn to the left, the centrifugal force will cause the shackles to swing, and the chassis will move to the right on the shackles. As the chassis moves to the right, the drag link will push on the passenger side steering arm, since the steering gear box is mounted to the frame. This will result in "oversteer", so you'll have to correct for this unplanned movement of the steering arm.

On a side-steer car, this movement of the chassis to the right during a left turn does not cause any unexpected movement of the steering arms, since the drag link is perpendicular to the movement of the frame.

In addition, at low speeds with a cross-steer car, as you turn the steering wheel to the left, the drag link pushes the passenger side steering arm to the right, and this pressure will push the frame to the left. All of these unpredictable movements in a cross-steer car can be prevented with a good panhard bar.

Side steer cars have different problems, since it is difficult to get the vertical swing arc of the drag link link to match the vertical swing arc of the front suspension. If these two arcs don't match, the difference between these arcs will cause the front end to be steered by this difference as the suspension moves up and down, or the dreaded "bump-steer". A panhard bar won't have any affect on this problem.

I have a question! Are there any of you guys out there in the Hot Rod Forum world that have a suicide front end with cross-steering? Let's hear your comments!!

Hotrodroy ---All of the cars that I have built over the years have used a Vega box and cross steering. I have always incorporated a Panhard rod, because I put one on the very first car I built 20 years ago, and it worked so darn good that I have never felt the need to build a car any other way. I have driven some of my friends cars with a conventional "side steer" system where the drag link ran directly from the pitman arm up to the drivers side front wheel. and I found that they tend to 'jerk" the steering wheel whenever you run over a railroad track, etcetera. I don't have that type of problem with the cross steer set-up. As far as a vega cross steer on a suicide front end, I haven't seen one myself, but then, I haven't been looking for one either. I know that others have the theory that a Panhard is a necessity on a cross steer front end, and maybe they are correct. I've never ran a cross steer without a Panhard, to know.

I know that others have the theory that a Panhard is a necessity on a cross steer front end, and maybe they are correct.

I sure needed a Panhard bar . . .