I've searched and read all the threads on this subject, but my question is still unanswered. I'm using a 4" drop tube axle and the srpings are mounted in place of the lower four bars. I took the radius rods and angled them in to act as both radius rod and panhard rod. I have been tolt that I need to run shackles for the springs to work properly. Is this correct?
No,not correct. What you have created is a "triangulated 4 bar" arrangement. GM used that idea on their mid size p***enger car rear suspensions in the 80's.There was at least one thread recently about triangulated 4 bars. Having a little rubber in the system might help though.
Ian is correct you don't NEED shackles, but they may help prevent bind if you don't have every thing in sinc. I am wondering if you have your radius rods on enuff angle (should be 45 degrees from axle) to limit side to side movemet especially if you are using cross steering ie. Vega box
Look at this... The answer is no, you don't need shackles. Shackles are used where the arc of the spring and the arc of the axle are different. In using the springs as the lower links, the arcs are one in the same.
Notice how the diagonal links on the Posie car attatch higher on the axle,to create a moment arm which resists the braking torque. Similar to how hairpins,or a typical 4 bar mount. -------------------------- If you were using a typical streetrod 4 bar,with 1/4 elliptics, like Zipper Motors,then shackles would be a good idea. Otherwise the springs,and axle,are trying to pivot in two different arcs at the same time,which will bind. -------------------------- Leaf spring rears don't need a panhard bar,so you shouldn't have a problem.
After reading the posts a couple of times I agree, shackles are not needed if the springs replace two of four radius rods. However, a quarter eliptic design based on four radius rods (like mine using an I beam axle) does require shackles in order to maintain the same caster throughout the axle arc of travel.... plus and minus axle twist Yawl anna gunna git dat pleesin sameness of caster angle witout dems fur bars an dems shackles. An den yous gunna learn bout Kepler's turd law of da conservation of angular momentum witch gunna translationed into da increase in da bump steer............. mooo.....well mahbee not so much on dem tubulary axles....... or mahbee more.
If your running just two radius arms out of 4 you CAN'T use shackles...your 1/4 Elliptics are acting as the other two radius arms to prevent axle rotation and must be solidly mounted to the axle...and of course the frame. Imagine for a sec that you have a regular front with a full 4 bar and coils. Now mount the lower 2 radius arms to the batwing with shackles... Back up hard and hit the brakes. See a problem? Well shackles on a front or rear leaf/link will have the same issues. As for angling the front radius arms enough to act as a side movement limiter...I doubt you can do it. I'd run a long, level panhard bar behind the axle and have done with it. Mount the radius arms for a tasteful appearance and let the panhard take care of the side to side stresses. Simple, solid and time tested.
Thanks guys. I used the posies truck when I decided to go this route. I thought that if I ran shackles, under braking, I would change the caster due to weight transfer. As for the steering, I fallowed hillbillyhells Ranger side steer tech article. My box came from a '78 Courier, but it's the same box.
Bill has a point on the panhard bar. If you use cross steering, it would be advisable to use one. That will extend the life of your suspension bushings if nothing else. Traditional steering exerts forces in the same direction as the vehicle motion, so adds nothing extra.
After reading all the posts I noticed that no-one is taking into account how the spring length changes as the suspension works. As the spring compresses under load, the effective length increases, if there are no other locating links holding the axle in place, the axle will move forward, lengthening the wheelbase. So when the spring flattens out under load the wheelbase increases, and tries pulling the drag link with it. Obviously the drag link can not grow in length so one of 2 things happen. Either the the steering arm turns to compensate for the extra length in the wheelbase, or the pitman arm turns to allow for the same. This is called bump steer. when you hit a bump, the suspension compresses the spring and the car steers!!!! If you use a single link with the spring, but without the shackle, when the spring flattens, the axle is held by the single link but the spring gets longer so rotates the axle, so changing the castor angle. If you are going to run a single link, such as a hairpin, or two links, as in a four bar, you need to run a shackle to allow thw spring to expand without affecting the wheelbase. Cheers, Stewart.
Just had to go there, didn't ya, Stewart... You are correct, but steering geometry can and should be designed to address this. The change in castor is not alltogether a bad thing. The extra wheelbase and added castor will actually lend a tendency toward keeping the wheels straight ahead. The placement of the upper link on the axle is important when using the springs as the bottom of a 4-link. If you can put the upper pivot point of the axle in line (or very close to) the line than runs from one spindle to the other, you will eliminate the variable of the drag link in a traditional steering system. In a cross steer situation, this is less of an issue if properly set up to start. Good point!
I'm understanding that the car is using cross streer, so the drag link is not an issue for bump steer. Castor change is definitely NOT a bad thing. Consider my Citroën 2CV. All four suspension arms are pivoted from a point some two feet in from the wheels. Think of an elephant's tusk for shape. The point contains the wheel attachment. Since it uses a kingpin, and the kingpin hole is drillled in the end of the tusk, when the suspension compresses it changes angle somewhat dramatically. And since the car has a lot of travel, and no anti-roll bars, the suspension moves a LOT. All the driver notices is a slight increase in the self-centreing of the steering, basically felt as increased effort. As a byproduct, the wheelbase also changes as you drive. Again, no ill-effect. What you must do is maintain the steering links in as near neutral angles as possible, meaning that the arms should all be parallel to the ground with the suspension in a normally loaded condition.
I was taking it into account...because if the spring is designed as it should be in this configuration, IOW to be almost flat at ride height, the effect you mention won't be noticeable! Leaf springs don't get "longer" as they work. The perceived length increase is the result of the arch flattening as the spring is compressed. If there is no arch present then the spring will keep the axle position stable in the normal range of suspension movement, without any perceived length increase...just like a solid radius arm in a 4 link. The positioning of the spring and overall length is important as consideration will need to be given to the effective working length of the spring compared to the length of the radius arm its matched to. Caster change can result if the lengths are highly mismatched. In normal range of motion some mismatch could be tolerated, but the closer the better. For things to get to the point where there are gross increases in the actual wheelbase of the vehicle, the suspension would have to be mismatched to its purpose beyond commonsense. (Common? LoL I know...) It's all workable if the angles and range of motion are considered. Actually, when you consider the length change of an arched semi-elliptic spring like in the back of a modern pickup you would think that you would get serious rear steer effect as the spring compresses... Theres only one shackle and both sides of the spring compresses and lengthens right? Yes and No. The front of the spring is mounted so that the bushing is close to the working height of the rear axle and the rear of the spring is so high that "in tension" upside down shackles are often used to compensate. The front of the spring, while arched along with the rear part if you were looking at one out of the vehicle, is effectively taken out of the picture just because the front spring section is mounted level. A length increase can't take place because the arch of the spring is cancelled out. These same considerations can be addressed to get a good leaf/link system IMHO. You can't run a set of twin bushed radius arms in a leaf/link system with a shackle on the spring because nothing will keep the axle from rotating under braking forces. With split wishbones or some other single pivot point setup you need shackles...but then the rotational forces are handled by the solid axle mounting of the wishbone and the spring is required to hold ride height only...and there will be a slight mismatch of arcs as the suspension works. Personally, I'm not convinced a shackle is really needed there either unless your using very small rubber bushings in your spring eye! We're not gonna see suspension movement like a rock crawler or something. Flat spring and maybe 7" of suspension range? I know where your coming from...but I think your taking the setup to the extreme in this case...
When using the spring as the lower link, where do you locate the pivot of the upper link? In other words, where do you consider the pivot point on the spring?
I hope this image works. Sorry for the art work... Ideally, the links would be parallel with the ends directly above one another. This is a side view so a triangulated arangment just needs longer links to make up the same lateral(?, front to rear) distance or functional length. This set up allows both links to have the same arc and preserves the castor angle. If a 1/4 spring is used as a lower link, the length is not fixed. Counter this by putting the front pivots as close to the true spindle center as possible, both vertical and lateral. Top never in front of bottom. The alternate X for the upper length is anther way to reduce the influence of the changing spring length. Move X down and/or forward to cause increased castor under compression (tolerable), or move X up and/or back to cause decreased castor under compression (not good). The longer any link is, the less it will affect castor, top or bottom. Remember that point B using a spring will be forward of the fixed portion of the spring that is in the clamp.
I was fallowing you up to this point. If I'm understanding correctly, "b" is actually going to be further away from the mounting point of the spring due to the fact that it will not flex/piviot where it is clamped. The flex will be a short bit further down the spring towards the spring eye. So how do I figure the length of the upper link without knowing exactly where point "b" is? And how do I go about finding point "b"? This setup is using a side steer and the upper links are/were going to be mounted or the uper portion of the tube beam closer to the k/p than the spring which is mounted behind the tube. The center line of the spring eye is is paralell to center line of axle. Does this help?
It took a while to find, but here's the link... http://www.jalopyjournal.com/forum/showthread.php?t=77658&highlight=ranger+side+steer
see my quarter eliptics they work really good, no shackles!! drove it for thousands of miles over a couple of years, The guy who bought it did so as it handled so much better than any other rod he had driven including an all independant 34!
Many thanks. I've tried searching several times since I posted the question all with no luck. Good stuff.
Ray, You've got a good handle on it. The pic from paulatxntric is cool in showing another alternative for angle on the springs. This is a the opposite of what I plan to use. The frame angles in on my A, so the springs will too, if I mount them in line with the rails. that means I get more net angle on the upper bars when they angle outward for additional stability. Another cool thing in the pic from paulatxntric is the way it clearly shows the effective working length of the spring back to the clamp where it becomes immobile. Note the similar length in the upper bar. Get to work and send pics so I can see how it turns out. I'm afraid mine will be a couple of months before I get that far. Scotty
http://www.jalopyjournal.com/forum/showthread.php?t=77658&highlight=ranger+side+steer TJM, Cool link! I'll be using that one.
Wish I could take credit for it, but it's from the main thread author. He deserves that thanks for the link to that great tech thread.
My set up is just like the one paulatxntric posted except that the springs are mounted to the tube axle with welded brackets, and the upper bars angle out to near the top of the beam (close to the k/p). The posies truck is where I got the idea to angle the top bars and mine is set up very close to that front end. Thanks again for the help.
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