Front pan hard bar on cross steer dropped axle?

[31blackcoupe]

AV8 project: 59ab in a '31 chassis-now moving on to the front end. Super Bell 4' drop axle, split stock wishbones, single leaf main spring, '37 cross steer box. Someone mentioned I should put a pan hard bar on that axle to prevent bump steer from the shackles moving side to side. All new parts except the wishbones. Using modern shocks also. Anybody running this set up or any thoughts on using the pan hard?
Thanks,
Art

[JSeery]

Did you consider a shorter spring? The spring should be under enough tension to stop any swaying. Of course Ford added the pan bar in later models to improve sway, but also with the longer spring to purch ratios.

Don't ever remember anyone referring to swaying as bump steer, but that is probably irrelevant!

[V8COOPMAN]

BUMP STEER is a term that is often mis-used, and mis-understood. Bump steer is usually a result of a drag link being "engineered" or installed at an angle NOT PARALLEL with the axle in the case of CROSS steering, or NOT PARALLEL with the radius rod(s) on a side-steer set-up. When the axle hits a bump and moves upward, the ANGLED drag link effectively changes the length when the axle moves vertically, and causes the spindles to change angle ("STEERING angle") in relation to the axle. SO, when ya hit a bump, the steering angle changes, while the steering wheel remains in the same position.......hence, "bump steer".

Without seeing pictures of your axle, etc., like Seery says, maybe a shorter leaf between spring eyes, to effectively cause your shackles to ride at an approximate 45 degree angle, bottom of shackles canted inboard. DD

[saltracer]

you could use what is called a dead perch also.

[31blackcoupe]

Originally Posted by V8COOPMAN

BUMP STEER is a term that is often mis-used, and mis-understood. Bump steer is usually a result of a drag link being "engineered" or installed at an angle NOT PARALLEL with the axle in the case of CROSS steering, or NOT PARALLEL with the radius rod(s) on a side-steer set-up. When the axle hits a bump and moves upward, the ANGLED drag link effectively changes the length when the axle moves vertically, and causes the spindles to change angle ("STEERING angle") in relation to the axle. SO, when ya hit a bump, the steering angle changes, while the steering wheel remains in the same position.......hence, "bump steer".

Without seeing pictures of your axle, etc., like Seery says, maybe a shorter leaf between spring eyes, to effectively cause your shackles to ride at an approximate 45 degree angle, bottom of shackles canted inboard. DD

Thank you sir.

[31blackcoupe]

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Originally Posted by saltracer

you could use what is called a dead perch also.

Thank you, the "dead perch" essentially eliminates the shackles the way I understand it.

[31blackcoupe]

Thank you gentlemen. I have the original front spring which sounds like the best option (maybe with a couple leaves removed). Once again JSeery to the rescue. Thanks again for all the help you've provided J.
Art

[JSeery]

Originally Posted by 31blackcoupe

Thank you, the "dead perch" essentially eliminates the shackles the way I understand it.

Not sure how that would work on a transverse spring. That would cause the axle to move in-board/out-board as it moved up and down which would in turn cause the spindles to pivot.

[Mart]

Hang on, every ford built between 1935 and 1939 had a transverse spring, cross steer and no extra measures to control sideways axle movement. The relationship between the spring length, the angle of the shackles, and the geometry of the drag link was judged perfectly acceptable.

I'd say just go with what you've got and see if you find a problem. If you do, you can consider a panhard rod or a dead perch. With a dead perch, one side of the spring effectively acts as a panhard rod. This might be ok if the angle of that side of the spring and the drag link are somewhat similar. Likewise if fitting a panhard rod, it should attach to the axle on the passenger side, and roughly follow the line of the drag link.

Hard to fit in on an open wheeled car as they tend to stand out.

Mart.

[V8COOPMAN]

Originally Posted by 31blackcoupe

Thank you, the "dead perch" essentially eliminates the shackles the way I understand it.

A DEAD PERCH essentially eliminates the shackles on ONE perch...one side ONLY! No way would the suspension work with TWO dead perches. Examples of a dead perch below! Get the MAIN leaf length and the shackle angles to 45 degrees or so, and things will get mucho-betterer! DD

[JSeery]

Coop as the spring is an arc and that arc changes as the spring moves how can it not move the axle in and out as the spring goes up and down?. I have never seen a dead perch used.

I'm referring to a solid transverse spring front Ford axle. I believe this is how a Chevy front axle works and almost all parallel spring rear axles I have seen.

[Fordors]

31, in your initial post you mentioned having a 4" dropped Super Bell axle and a mono-leaf front spring. S/B makes a few different axles, for example they have a 48" king pin to king pin that is 36 3/8" between perch centers and they also make a 46" that is only 34 3/8" between perches. Depending which axle yours is will have an impact on spring choice. To select a spring width (eye to eye) measure the distance between the perch holes in the axle and then subtract five inches, and typically this will put the shackles near 45°. If you have the 46" axle your stock spring will be too wide to work, but I think you might be OK with the 48" axle. I did not use a Panhard on my coupe and it has Vega cross steer, Model A dropped axle with reversed eye spring and shackles at 45°; handles great.

[31blackcoupe]

Originally Posted by Fordors

31, in your initial post you mentioned having a 4" dropped Super Bell axle and a mono-leaf front spring. S/B makes a few different axles, for example they have a 48" king pin to king pin that is 36 3/8" between perch centers and they also make a 46" that is only 34 3/8" between perches. Depending which axle yours is will have an impact on spring choice. To select a spring width (eye to eye) measure the distance between the perch holes in the axle and then subtract five inches, and typically this will put the shackles near 45°. If you have the 46" axle your stock spring will be too wide to work, but I think you might be OK with the 48" axle. I did not use a Panhard on my coupe and it has Vega cross steer, Model A dropped axle with reversed eye spring and shackles at 45°; handles great.

Great information Fordors!
just measured and my axle is a 48", the spring perches are 36 3/8" apart. I think I'll leave it alone and see how it rides. Sounds like I might have the right combination.
Thanks a million,
Art

[V8COOPMAN]

Originally Posted by JSeery

Coop as the spring is an arc and that arc changes as the spring moves how can it not move the axle in and out as the spring goes up and down?. I have never seen a dead perch used.

J.......I'm not disagreeing with ya. On a transverse spring (old Ford), the axle will move left and right as the spring's ARCH increases or decreases with a dead perch. Dead perches are only legitimately (maybe REALISTICALLY is a better word) used on roundy-round cars, and MAYBE 1/4 mile cars.....MAYBE! DD

[JSeery]

Originally Posted by V8COOPMAN

Dead perches are only legitimately (maybe REALISTICALLY is a better word) used on roundy-round cars, and MAYBE 1/4 mile cars.....MAYBE! DD

Ok, the light just went on!! I have seen them used on dirt track cars! Had totally forgotten about that. I'll been around the torsion bar cars for too long.

[JWL]

Those pivoting perch attachments work great in pairs. I went to allot of trouble to design and build a set for my 1940 front end. The purpose they serve is to allow the axle to travel in the natural arc without deflecting the spring, shackles, bushings, u-bolts, frame, etc. Ride quality is improved. I did install a panard bar, also.

[BLACKNRED]

Originally Posted by 31blackcoupe

Thank you, the "dead perch" essentially eliminates the shackles the way I understand it.

A dead perch only allows the axle to move in one direction.
Panhard bar set horizontal at ride height allows the suspension to operate normally with little or no movement side to side.

[JSeery]

Originally Posted by BLACKNRED

A dead perch only allows the axle to move in one direction.

Guess that is going to depend on your definition of "one direction" the axle is going to move in and out as the arc of the spring changes. The spring is fixed at the center mount and the end of the spring moves out as it is compressed (decreasing the arc) and in as it is decompresses (increasing the arc). If a dead perch is attached to the spring it is going to move with it. In a normal shackle arrangement the shackles allow both ends of the spring to move in and out but not the perches.

With the tension in the spring at the shackles the axle stays centered with the spring. In later years where there is more movement allowed with less static tension in the spring shackles a locator or panhard bar was required.