I am building a 36 Ford panel truck for my dad, this is the first time I have ever built a rod with a straight axle. The truck has a 4" drop axle with disc brakes, and a stock wishbone, that was installed when he got it. I have been trying to decide on what to do on the front suspinsion, a 4 bar or split the wishbone. I have heard pros and cons on both so now I would like to here from some fellow hambers on this subject. Thank you in advance Al Hammond II
are you trying to lower it? If not, I'd leave the wishbone if I could. Then my second choice would be the split wishbones. But with full fenders it really won't matter. I think the split wishbones offer more sway stability without the use of a sway bar. You'd still want a panhard bar to locate the axle. A wishbone has a panhard built in. Parallel four link would let the frame roll and you'd need a sway bar and panhard rod.
I'm with Tudor in that if you can leave the stock wishbone, do it. But if you're installing any kind of a more modern drivetrain you probably can't. If your debating 4-link or split wishbone, run hair pins. They offer more adjustability than a wishbone and is more traditional than 4 bars. It also doesn't require a panhard although it won't do any harm in any case since with withbones or hairpins you are counting on the spring to center the front suspension.
That's because with split wisbones the axle is acting somewhat like a torsion bar to provide some anti-sway action How do you figure that? An un-split wishbone (or a split one for that matter) doesn't provide any side-to-side limitation on axle movement which is what a panhard bar does. A parallel 4-link will allow a bit more frame roll than split 'bones because the axle isn't acting like a torsion sway bar but you probably don't need a sway bar for normal driving and you probably don't need a panhard if you aren't running cross steering. There are a lot of cars with "conventional" steering without panhard bars. (Like stock Model A's for instance.) If you do need a way to limit side-to-side axle movement you could use a dead perch on one side instead of a panhard.
Good idea, but I'd have to disagree on the idea that hairpins don't need a panhard. If you are running cross steering you will still need some way to limit side-to-side axle movement which comes from the movement of the spring hangers. That's why a dead perch works to limit side-to-side movement, it replaces one of the spring hangers.
smokie - you are right,with a wishbone the axle could still swing laterally in the spring shackles - my point was supposed to be that the wishbone offers a good brace to the axle.
You're right there. IMHO, a (non-split) wishbone pobably gives the suspension the best "terrain following" capability of anything except a parallel 4-link and I can see reasons it might even be better than a 4-bar. Of course with modern roads the worst we usually have to deal with is not hitting the speed bump square at the "Golden Arches" drive thru. Most of the reason for splitting 'bones was to gain clearance for modern engine trans combos. Several suppliers are now making trans mounting plates that keep the suspension geometry very close to stock (i.e. keep the ends of the split 'bones very close together) and yet allow the use of newer eng/trans setups. Maybe this would be a good way to go for 36panelman. He doesn't really say why he wants to change what is already on the truck. Different engine?
Is the 4" dropped axle a tube axle? I have heard you shouldn't use a tube axle with a split wishbone, because it can't twist like an I-beam axle.
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