***I posted this question in an old thread of mine, but thought a new thread might help it get answered.*** I've got another question on 1/4 elliptics. In this design, using the radius rod and leaf as a four-link, the radius rods are angled. It reads this is to prevent binding, but in a "normal" 4-bar front the upper and lower rods are parallel. How is this design, with the spring acting as the lower link, different and why does it require the angled upper link? Thanks.
http://www.jalopyjournal.com/forum/showthread.php?t=433843 not that it's related to the ? but this car is how I became interested in 1/4 Elips... http://www.streetrodderweb.com/features/0802sr_jeff_eischens_homebuilt_model_a_tub/index.html
The angled upper link is designed to help eliminate any side to side motion. Similar to a triangulated 4 bar suspension on a rear end.
Triangulated 4-bar setups are set up diagonally so as to keep the axle located laterally, eliminating the need for a panhard rod. In the actual photo above, a panhard rod would be redundant, as the radius rods are in a minimal, but actual diagonal plane.
That makes sense! Not to hijack your thread, HRS, but I've been looking at a particular elliptical setup and could use some of this same expert advice. Here's a drawing of what I'd like to do at some point. Now the people I've asked so far have been divided on whether I would need 2 upper links (like what we're discussing here) or not. The division seems to be over the fact that, given that NO EYES ARE IN USE (read: leaves are bolted to plates on the frame and axle) that this 2-link set is adequate as-is. I can see how the pinion angle on the rear-diff might change under torque from the motor, though. However, look at this original IH set up. It looks to me like just a set of quarter ellips with non-attached overload springs on top. Thus, is pinion-angle-change (rotaion of the axle) not something of concern afterall? Here's what I'm pondering on doing: Here's the example of what's been done:
Most people don't realize how much leaf springs deform under lateral force. Triangulating the upper radius rods is the right way to go. You can get away without triangulation when you run 4 quater elipticals like a miller race car because the collective stability of the 4 spring packs is so much higher than two. It's just a matter of tolerance.
What about when you run a full wishbone or hairpin radius rod in addition to a leaf spring? Like in a more "traditional" 1/4 elliptical set-up like these... There is no triangulation there...does the full length radius rod compensate for the lack of triangulated top link?
Johnny, your right man! How I missed that, I have no idea! The natural inclination of the radius rod forms the triangulation. I am dense sometimes.
HRS, what if you replaced your two upper "triangluated" arms with a single, half round or oval shaped bar of 180 degrees that attaches at the same place on the frame but only to one place at the center the front axle? It would almost look like a nerf bar, but be a functional part of the suspension. I'm thinking of something like they use on drag cars - a V or Y shapped link that runs below the driveshaft and in front of the diff. As long as you could keep it away from the grille shell it might be plausible. Gary
Here's another article to snoop... before... after... http://www.streetrodderweb.com/tech...sing_posies_elliptslide_spring_kit/index.html
Do the springs attach to the front axle with a shackle? Not clear in the photo. If they don't, isn't that just a fancy solid suspension? Also, how does it handle articulation? By the threaded rod end rotating in its sleeve?
Impossible to tell from that photo, but I would bet that the lower springs on that IH truck are standard semi-elliptical, not 1/4s (note the pivot pin in the front hanger). Setups like the one you propose have been done before, but you may have a lot of pinion wrap and wheel hop with any kind of real torque to the wheels. Keep in mind that the pinion goes up under power, so the spring pack is arching against gravity (vehicle weight). Only the leaves that are actually bolted to the axle have to bend, unless the entire pack is clamped together (VERY rough ride...). Regarding the usefulness of triangulated upper links with 1/4 ellipticals, it really depends on how much arch the spring pack has at ride height. If the springs are relatively flat, then the attached leaf (or leaves) have to bend directly sideways to allow the axle to move side-to-side. Not likely! The more arch the pack has, the more the spring leaves can twist and allow axle movement. This is the same problem lifted 4X4s with high-arch springs encounter in corners... IMO, the ideal way to use 1/4 elliptics is with shackles on the axle and separate links, as shown here: If the shackles are plated (reinforced, not chromed), a fairly flat spring pack will resist side motion just fine on anything short of an autocross car. The real issue with solid links on any type of leaf spring system is conflicting motion. The leaf springs try to move the axle through a certain arc. Unless properly designed, the links can cause unwanted axle motion or binding as the try to force the axle into another arc. The picture in the OP is a good example... IF the suspension uses much travel (I'll admit it probably doesn't), the arched leaves will flatten out and push the bottom axle brackets forward. The top links are already flat, so the top brackets will begin to arc to the rear, resulting in a LOT of caster angle change.
I REALLY LIKE THIS SETUP! CLEAN AND SIMPLE! One thing a person does need to remember when triagulating links to eliminate "side to side", is that the closer the top links, or angled links are to 45* the less the chance of this side to side sway. Any triagulation is good, don't think I'm nay saying in the slightest, all of these setups will work, and work well. Just the little bit of advice I can give, but remember, I'm not a doctor, just an asshole...
You.re on the right track. I'll say it again - if those front shackles are welded to the axle (in the lower photo - hard to tell for sure) then there is NO SUSPENSION in that car, except for whatever you would get by the various parts flexing. Think about it.
The other thing that really bothers me about the setup below, is that the top links are swinging on planes that are not parallel, so the points at which they attach to the axle CAN NOT remain equal-distant from one another. In other words, the bushings on both ends of those links are always going to be binding as the suspension moves. They are not using heim joint or similar there, which would solve the issue. They look to be using polyurethane, which has a little give but I don't believe that material is meant to be used in the way they are using it there. Basically, I think this setup is just wrong. James
You can't have shackels on 1/4 elliptic springs in that setup or the axle would be free to swivel.Just think of the spring as the lower link in a 4 bar front end.
Plym49 is correct. See my response above. If those top links were mounted on bearings such that they could ONLY travel along paths defined by an axis represented by the bolts that hold them on each end, there would be absolutely no suspension in the car. The ends of those top links, on the axle side, MUST diverge as they swing. Being that they are mounted firmly at a certain distance from one another on the axle, the suspension can only move via bushing flex. Thus, on paper, the suspension geometry of that car CAN NOT move. It only moves in real life due to flex of parts that shouldn't.
Exactly. If those upper arms were replaced by another set of leaf springs, it would be OK since the springs are designed to flex. The setup pictured is just a really complicated way of building a solid front end.
This front end will work fine as is, it looks like it has around 3-4 degrees of caster sitting static on the frame table. When under load, like others said it will have a caster increase, but so would a transverse spring with bones or hairpins. The longer the locating links, springs,bones etc. the less caster gain. The urathane bushings are stiff but all components will flex, including the axle just as an ibeam with split bones does although the ibeam will flex more than the tube. This design is stiff or resistant to roll, like a sway bar it works fine up and down in a linear motion but binds when trying to lean. A better design would be to make a wishbone or three mounts for the top link, say leave the urathane rear bushings and put a heim or sepherical bearing right in the center of the axle with one mount and all would free up. This may not have been done because of radiator or grille clearance.
Yes, that axle will see extremely significant caster changes as that thang strains and flexes. That is hardly 'working fine'. It is in fact a major hack. Just because someone cuts pretty brackets and can lay down a nice looking weld does not mean that it is designed properly. From what we can see, that front end is as much a hack as something cobbled out of TV antenna tubing with pigeon sh1t welds.
Thousands upon thousands of triangulated urathane bushed rear four bar suspentions have been installed and are running around and work fine, and when they go through suspention travel the pinion angle changes. There is allways a better design for something, many different designs work, some just work better.
Ironically Jeff Eischens is a member on this board and will be at the shop today. I'll pass along this thread to him and maybe he can chime in and help
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