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Some thoughts on suspension...
I like the descriptive phrase of "saw steering" that
Mark (427435) brought up. Good way put it.
The F-53, with an I-beam axle, must be similar to smaller, older 4X4 trucks with a live front axle.
First a preliminary look at experiences I had with a couple of 2000 Ford trucks I owned that
should have steered identically:
I still own a 4X4 Excursion which still has the original, non-greasable ball-joints (no zerks). The passenger joint has some minor play but the truck steers well for now in spite of worn joints and shocks. In contrast I also later bought a 2000 4X4 F-250 that I pre-noted already had new aftermarket greasable ball-joints, which I thought was a plus, since heavier diesel trucks are noted for wearing ball joints.
Unfortunately the F-250 greasable, after-market ball-joints were steel-on-steel and they did not turn as easy as the slippery OEM Excursion joints which are permanently pre-greased and purposely have a durable plastic cup in them to do so (design allows no zerks). The result was that the F-250 never did steer as well for me as the OEM equipped Excursion. The F-250 steering was slightly sticky resulting in subtle "steer sawing" that Mark (
427435) mentioned above, which kept it from naturally going straight. I actually measured a steering effort difference between the two trucks, while tires were off the ground, using a scale to operate the steering wheels dead-engine.
The problem is that sticky steering does not return to center properly, the sole function of having caster settings at all... tuned to forward motion of course. Such a "sticky" truck steers as though it wanders easily and requires constant attention to correct any road surface change at all. This can be very stressful to the driver which is fatiguing.
In conclusion, if I replace Ford ball-joints on the Excursion, they will be the factory engineered OEM joints. Even without zerks, OEM parts are good for another 100k. They all self-center as they wear, maintaining alignment and many are changed out prematurely because of yet-acceptable minor play. If slipperier ball-joints (or better lube) are available for the F-53 chassis, that would then be my choice also.
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FYI, I note that one fix given here is to increase caster settings from 3 degrees to 4+ degrees. While this fixes automatic steering centering by overpowering the stiction, it will make steering in reverse harder since the caster wants to flip the steering around more aggressively while backing, just like a grocery cart. This is usually a small price to pay, but could make it harder to back a longer distance should one need to back out of a long, narrow road. Ideally the steering would flat-out have very little stiction and, while at high forward speed, a very mild caster would be enough to assist moving straight in ones own lane... without being detrimental to backing up.
Another popular fix besides increased caster, is to increase the sway bar setting. First of all, the greater nuisance of frequent sway may be caused by "saw steering" in some instances, so in these cases, increased caster is really a cover-up of the root problem. The downside to increased sway bar settings is that ideal soft ride suffers some. This occurs because if one front wheel hits a bump, part of the impact is transferred to the other front wheel making the absorption of the bump compress double the springs instead of one. Result... stiffer ride.
One way to heuristically imagine this is to imagine that the sway bar is absolutely solid. If the right front tire hits a 3" rise, the solid bar forces both the right and the left front spring to compress equally, about 3". Both springs transfer the jolt to the chassis. In turn the chassis transfers the impact to the passengers twice as stiffly. Since sway bars are not typically solid, transfer to the other spring lies somewhere between no transfer at all (no sway bar) to partial, a function of the sway bar travel stiffness proportional to suspension spring. But any sway bar always
decreases suspension ride compliance; i.e. rides rougher.
Increasing sway bar tension can also cover up a problem with bump-steer if it exists. Bump-steer is a condition whereby the toe-in changes with suspension spring compression/decompression. This appears when the truck leans during a sway maneuver and the spring compression change affects geometry of the steering tie-rod, which in turn pulls the toe-in setting out of alignment. This can cause a darting reaction that makes the sway escalate much worse and demands a frantic correction, or series of corrections, from the driver as though he is walking a tightrope. Very tiring and worse, hard to intuitively recognize the precise root source from steering feel. The truck just plain steers bad, that is the unsophisticated overall feeling.
Wes
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