Front sway bar

[63sbssbbw]

I understand what your saying Rick....which leads me to a question
If there is NO preload,would that not transfer into what would feel like slop in the torsion bar,ie bar not being effective until AFTER you've started into a corner???
Not a pro at suspension or anything,just trying to understand it better
Something no one seems to have addressed is the new coil springs(well,they look new),are they the correct ones??...Will they "settle in" once everything's all together(incl. sheetmetal)??...Just a thought
Thanks,T

[ValveTubeHead]

Originally Posted by 63sbssbbw

I understand what your saying Rick....which leads me to a question
If there is NO preload,would that not transfer into what would feel like slop in the torsion bar,ie bar not being effective until AFTER you've started into a corner???
Not a pro at suspension or anything,just trying to understand it better
Something no one seems to have addressed is the new coil springs(well,they look new),are they the correct ones??...Will they "settle in" once everything's all together(incl. sheetmetal)??...Just a thought
Thanks,T

I suppose it depends on what flavor of slop you're referring to; prior to turn in...ride quality and feel in a straight line would probably be best addressed with springs/dampers/tire/alignment refinements. I think sway bars actually reduce straight line ride quality to a certain extent....I mean if we lived in a world where we didn't turn, I don't think we'd need sway bars. Cornering and turns are much more complex though: all of a sudden chassis stiffness, sprung and unsprung mass, CG, geometry, linkages, spring rates, dampening force, tire sidewall stiffness, caster/camber, positive axle location - etc. etc. etc. become much, much more important

Aside from the torsional stress introduced at the mount points. I think a relatively hi preload will introduce less than optimal geometry to the front suspension...perhaps more bump steer, reduced ride quality via pronounced transients. I think modest preload is not uncommon; adjustable preload even preferred, but from what I've discerned from reading/seeing 63chev's situation ...I would probably attempt to get as close to neutral in the static setup before proceeding. New/shorter springs will certainly effect the respective geometry... may be the source of all this headscratching. dos centavos

[rickf]

If you were only driving straight and there were no other forces involved (say, like a gusty cross wind) then you'd get the best ride with 4 wheel independant suspension and no sway bars.

The sway bar is a connection between left and right suspension. A preload would mean to apply a difference in position from left to right. If you were only turning one direction, you just might want some preload. The dirt oval track race car is an example where one might tune the suspension with some preload to optimize left turns, since that is all there are on the track. But most public road vehicles need to turn both left and right, and so a balanced system (no preload) is the usual way to go.

Back in the earlier pictures where the sway bar is shown on a jack with some 3 inches to go to the frame, that is not a preload situation because it is the same on the left and the right. To meet the frame the bar needs to be jacked up evenly. If you want to give it preload, then put a 3" spacer to fill one side and jack up the other side. That would twist the torsion bar, making preload. The better way to apply preload, though, is at the swingarm mount (raise or lower), rather than making the frame mounts deal with some misalignment of the shaft. An effect of this preload is the vehicle is not flat when in the neutral postion.

What is that sway bar actually doing? When the vehicle is going straight, the load on left and right springs is the same (let's keep it simple, static vehicle is perfectly balanced, driver and passenger weigh exactly the same, load in the back is perfectly even, etc). WHen it goes into a turn centrifugal force causes a weight transfer. Now outside spring is supporting more weight and wants to compress. Inside spring is supporting less weight and wants to extend. Together this causes lean, aka sway. The sway bar connects the springs. When one compresses, it tries to compress the other. When one extends it tries to extend the other.

From the outside spring point of view, the outside spring being compressed by the load gain from weight transfer is shifting some load via the sway bar to the inside spring, which now has "extra" capacity because weight transfer reduced its load and it is trying to extend. This "reduces spring" on the inside (so tries to keep inside from raising) and "adds spring" to the outside (to keep outside from compressing). It is a balancing act. It is not 100% 1-to-1 transfer, because the sway bar itself is a spring and "absorbs" some of the transferred force.


Back to the patient, somebody else mentioned that it looks like a lot of stuff is missing from the front end, potentially significant weight. It is likely that the sway bar is formed to "fit easy" when the suspension is in some normal neutral position, and that perhaps as it sits now it is more toward one of the extremes of travel, and so the bar is hard to fit. I suggest adding some 400 lbs to the front end (2 or 3 pals standing/sitting on it) and see what effect that has.

[63chev]

Man. Thanks for all the help. I do not remember what year truck I got the bar from but it had to be around 1978 to 1988 and it was a 3/4 ton, definitely not lowered. It was the only sway bar out off 20 or more in the yard that was the bigger diameter so I grabbed it. I first tried the brackets that were for lowered trucks because mine is 2.5 spindel drop. But when they were not even close I went back and traded them in for the much longer ones that I am trying now. My brackets look like all of yours but your rubber is not distorted. I tried about two hundred extra pounds on the front end and did not gain a half an inch. I am only missing the fenders and grill and basket. The springs sound like a good option but the last thing I want to do is disassemble when I have so far to go so I would like to try everything else first. The springs were the old ones from the 72 just blasted and sprayed. I probably would get a better ride with new springs anyway. I will try to bolt it to the frame first but the consensus is that too much strain in the neutral position is not correct. I am questioning the fact that I have 1972 front end on a 1963 frame. It has not been the easy "bolt on" I am a novice) that I heard it was and maybe this is another case where I need some modifications. Thanks again for all the help, I will let you know how it turns out but don't look for it quick.

[ValveTubeHead]

m 'perspective on "preload" in this situation while evenly distributed, is nonetheless preload of a spring; storing energy...presumed hundreds of pounds worth in 63chev's situation, based on the amount of described jacking force to locate the bar to chassis mount points.

By same token, Ive never bolted on an antisway bar that didn't offer some modest resistence at endlinks/bushings with the suspension in static-neutral state...for intents and purposes this specific "preload" would be fairly insignificant; nevertheless adjusting preload with or without l/r bias will certainly affect handling characteristics...swaybars are no less springs, just a different style to store and transmit energy.

ymmv

[63sbssbbw]

Thanks Rick and VTH,Had to read it twice but I think I've got it.
Following along here because I will be doing this in the future ('75 1/2 ton on a '63 GMC 1/2 ton) would like to see it solved so I know what not to do,
But your right Rick.....Back To The Patient.
T

[rickf]

Originally Posted by ValveTubeHead

m 'perspective on "preload" in this situation while evenly distributed, is nonetheless preload of a spring; storing energy...presumed hundreds of pounds worth in 63chev's situation, based on the amount of described jacking force to locate the bar to chassis mount points.

I agree that if the sway bar itself is flexed in any fashion then there is some sort of preload. The problem with the situation at hand is I doubt the sway bar itself is going to flex.

The frame mounts are the fixed point, relative to the swingarm the sway bar pivots around the frame mount. The swingarm swings an arc, but not in the same plane as the sway bar. So the distance and angle from swing arm sway bar mount to frame mount will vary. The joint on the swingarm is designed to deal with that motion, it is flexible to some degree, it is a "wobble" joint.

The sway bar end moves in and out (forward and back) as well as changes angle up and down.

Jacking up the sway bar evenly is going to try to bend the sway bar between the swingarm mount and frame mount. But the swingarm mounts are not rigid/firm enough to bend the sway bar, the rubber in the mounts is just going to flex (by design, it is their job). This puts a load on the mount in the neutral position as if it were at an extreme of the travel.

I doubt it will reach a point where the sway bar actually flexes, so it seems unlikely any "preload" will result. It is just putting a bind on the swingarm mounts. If it remains within the intended range of motion, then probably nothing bad will happen. If it exceeds, then the mount will wear quickly and/or break.

[mnky30]

also those srrings might be for a 3/4 to not a 1/2 ton that spring rate of a 3/4 is a lot higher then a 1/2 ton spring. you might want to count the coils in your springs and measure the thickness of the sprong to see if it is 3/4 ton or 1/2 ton springs

[63chev]

My springs have 7 coils and are around 1/2 inch in diameter. That's 1/2 ton front end in my pics isn't it? I guess someone could have put in different springs before I got to it but it sure looked rusty original when I got it.