I'm hoping someone can give some help with this. We've built a bobber truck with quarter elliptics front and back. Both ends have shackles and are located by basic 4 bar setups. Everything is square, toe-in is correct, tire pressure is good. BUT, when we accelerate hard the truck goes left, then deccelerate it goes right. Controllable but scary. Regular acceleration/decelleration is fine. The spring are cut down from older cars and have the same stack height and appear to have the same curve. But there are used springs. I'm thinking that the springs, since they are used, may have some different rate characteristics due to use. Let me know your thoughts! thanks!
Like others said, need some pics. What do you have for shocks? Basically you have torque steer. Under hard launch the left front tries to lift driving the right rear into the pavement and that gives the right tire greater traction and pushes the car to the left. Lots and lots of possible causes and remedies, need to figure out the right one.
Is there a Panhard Bar anywhere in your design? I've see pictures with quarter elliptics and the axle way out front. What keeps those springs straight without a panhard bar?
Sounds like drag link is traveling in a different arc than the steering arm on the spindle. The diverging/converging angles of the two will cause the car to wander as the suspension works up and down. For a complete description read the Science of Straight Axel here...... http://www.streetrodderweb.com/tech/0902sr_science_of_straight_axles/viewall.html
Check the car for "square". If the right rear tire is 1/4 inch ahead of the left, it will do what your car is doing, plus wear tires.
Can you post up pictures. I am putting 1/4" on the rear of mine and don't want to run into your issue.
Panhard bar not requird on 1/4 eliptic. The springs which are fastened in the spring plates do not allow any side movement. ME? I would nix the bottom bars and the shackles and do it the way 1/4 eliptics were intended to be. When I build them and I have done three now I use the spring as the bottom bar. The spring locates the axle both longitudinally and laterly and the upper bar controls the caster Don
Thanks for the input, people. I'll try to get pics tonight. We tried using the spring as the bottom bar and it was REALLY scary! figured out that with the open diff that the rear axle was causing the "torque" steer. When the springs flattened on the right side it would go left and under decel it would switch and go right. Going to shackles helped but it still torque stters enough to make you want to hold your breath. It's a drag link steering setup and the chassis is square. As for bump steer, this only happens when you hit it hard. Regular accelaeration it's fine. ARRRRGH. More later. Thanks!
Yeah, I bet it does it severe when you get on it. The drag link connecting your steering box to the spindle is probably a bit longer than your four bars, the two are going to swing in different arcs and hence the bumpsteer.
my 62 vette was doing the same thing--added a panard bar ,new spring bushings,rebuilt the front sway bar,ditched my locker for a spool,checked motor and trans mounts,chained the motor down,new heims on my traction bars,still scares the hell out of me when I let off the gas---has stock steering and suspension---still looking
I'm thinking you don't need shackles with the quarter elliptic an springs and 4 bar. This car has Quarter elliptic springs and split bones with no shackles and is said to drive pretty nice.. I may be all wrong but I have to think that shackles on the quarter eliptics are letting the axle (s) move around more than you want them to. Somewhere in my photo archives at home I have several photos of Mike Minnett's T bucket that had quarter elliptic springs on it in the early 70's and drove like a slot car.
Yes, get some pics. I am very interested as i am doing a 1/4elip myself and with the talent showing up on this thread i will learn me something.
The 1/4 elliptic spring set up on my modified has shackles ,since the springs and bones are different length they travel different arcs ,which stresses both the axle and the wish bone. The shackles allow the axle to move slightly without binding . I should also mention that this is my front front end setup. ................Jack
on the rear an uneven 4 bar works best, as the upper bars triangulate and prohibit a side to side movement. On thr front, I would add the panhard bar, that was previously suggested. Paul
I have tried to read into this post due to the lack of picture reference most responses require speculation. Here is my take, As mentioned you have a rear steer issue upon acceleration and that the lower locating control arm was the spring. Well that wont work and it is the source of your steer issue. Since the spring flexes it changes the arc travel of the rear axle , pushing it rearward or forward upon bending. This skews the rear axle pointing left or right depending on the flex side and there is no way to remedy the issue with out going to a fixed link lower rod. No shackle nor panard bar will fix anything. To cure your issue you will have to connect the lower pickup point on the frame and axle with a control rod (front to rear). Both your upper and lower rear bars should be as long as possible to minimize the swing deflection. Your lower spring can operate thru the same axle mount as long as it has some ability to freely flex, slide on a pin or piviot with a shackle and move freely independent of the axle mount. Some minor rear end engineering and you should be able to cure the problem.
my .2$ on my austin healey sprite that has 1/4 springs on the rear, there is a upper arm and lower spring with no shakels also a panhard bar to center it. very old school set-up
Same here, on my rear. I haven't drove it a lot (waiting on legal paperwork/title) but I have launched it hard and run to the top of third and it hooks up good and stays straight. My springs are old. Main leafs are 46 Ford pickup fronts with a couple 39 International rear leafs added.
If, as you stated, it has a true 4 bar and the spring is "just a spring", you shouldn't have any sort of windup or axle skew issues. I'll add my vote for a front bumpsteer problem. Oh, did anybody mention PICS WOULD HELP?
I race a bugeye sprite. I will tell you that one does need a panhard bar or some sort of lateral locating device on 1/4 springs...they move a lot when they twist. It was not needed when the bugeye had little 3" wide tires and 45 hp. Put some sticky new tires and 100 hp to em and they need a panhard bar. In fact the kids in my high school shop class are building a bobber and have designed and fabricated the 1/4 eliptical sprung de dion tube rear suspension using bugeye rear springs. It will get a panhard bar too. It is also using a diff and drive axles and hubs from a 07 chrysler 300.
This is exactly the case! An alternative to a panhard is well triangulated suspension links, such as when the quarter eliptical springs are used as the lower links in a triangulated four-link. I your suspension us a parallel four-link or four-bar, then you MUST have a panhard bar, even with quarter eliptical springs.
Scotty, I've done the QE front with hairpins and no bar, BUT I used bridged shackles and the spring packs were clamped out to the main leaf. Otherwise, the springs will flare.
Not trying to hijack this thread, but would like to understand 1/4 eliptic springs. Exwest could you explain spring flare. I know 1/4 springs have been used forever in production cars the Sprite being one example. My personal opinion is 1/4 either overstress the spring or the frame mount, when one wheel goes up and the other goes down. Because the spring is very short a pretty big twist is placed on the spring. Parrall leafs also get the twist but they are a lot longer overall and have rubber bushed attachment. Just trying to understand!
Back again, this discussion is not about a front end but a rear end and the rear steer generated by the skew movement of the axle as the lower spring flexes and changes dimension under load or unload. If you are using a spring as a lower control locating point, this point changes as the length of the spring changes. The rear axle is only square at one point in time and constantly changing skew as the chassis moves up and down. Lateral ridgidity is developed by the spring width and the thickness of mounting brackets on the frame and axle housing. Mounting the ends ridgid actually turns the width of the spring into a mini panard rod that locates the lateral movement of the axle. Can you run a panard rod , well yes but mostly its along for the ride. The biggest issue is developed with the length spring and size of the spring arch. As the suspension is located thru the lower mounting point this spring is always changing the wheel base length as it flexes and depending on bump or drop the wheel base can be different from side to side and that is when you feel the rear steer effect. Ridgid or stiff springs flex less and change dimension less but give harder rides while masking a design issue. This skew can be addressed to some extent with a soft bushing or shackle but the axle still skews somewhat usually creating an understeer condition. The best approach is to use an upper and lower control rod and let the spring float freely using a separate shackle or slider. Here is a diagram of what is happening.
Just for sake of converstaion Dick, why would a rigid attached spring be different from the lower bar of a 4 link? The rear travels in an arc there as well.
Think about it, to be a spring it has to flex or its just a hunk of steel, if it flexes it changes dimension.
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