Split wishbone suspension

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GBS
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Post by GBS »

Hey Choco, reversed wishbones? I think things are starting to get a bit complicated now. If you set the front end up the way Hans has done it, that means the only thing keeping the axle square to the centre line of the chassis is one transverse spring with a shackle each end that is not designed to give any sideways support. If there is any difference in the efficiency of the brakes, as there often is, you will have one side trying to pull back more than the other, the axle will move around as much as the slack in the shackles will allow and the car will behave like a 1901 tiller steered Whatevermobile.

Under hard braking the axle is likely to try and bend at the attachment point in the middle, bow out the tie rod and increase toe out. This could also do interesting things to the feel back through the steering wheel.

I canít see the car being anywhere near as good as Hans claims it is.

I have never seen this type of system used on a rod before but it is common on rear suspensions where the wishbone acts as a panhard bar. The axle is always located by some kind of four bar system at the outer ends though.

When we all start baffling ourselves with science over suspension systems, Peter usually comes in and sorts the lot of us out so this reversed wishbone system might be a good one for him to comment on. What do you think Peter?

Brootal

There is really no reason why a beam axle in a rod cannot have as much travel as any stock suspension. My A has a T bucket style front crossmember and has so much travel I decided to put small bump rubbers on brackets off the front of the chassis to limit the upward movement. I think it all depends on what you want to do with the car.

The emphasis these days is on street use and with many rodders heading off on interstate runs on all types of roads, driver comfort should be the number one priority unless you donít mind arriving sore and sorry with your teeth shaken out. It is simply a matter of designing the car to suit your requirements.

Peddro

Donít fall into the trap of thinking because someone has been doing something for years then it is ok. Countless people have got themselves into all kinds of engineering and financial disasters by following what a mate has done or what they saw in a magazine without looking thoroughly into how it works or the practicality of it.

Split rods and tube axles have been a big no no in rodding for as long as anyone can remember. While one rodder has been using them for a while and thinks they are ok, as sure as can be another one somewhere in the world has had a catastrophic and maybe tragic failure with them.

Brian
peddro
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Post by peddro »

GBS: Can't say I'd ever use a tube set-up REGARDLESS. I'm no master of engineering by any extent so will only be going with the most proven, reliable and safe HOT ROD (not street rod, read: no IFS!) front end, I can have, BUT to label anyone as a menace, I believe, is possibly wrong. For some reason, that set-up works, however (engineering-wise) WRONG it may be. To each his own.
[url]http://www.kustomink.com.au[/url]
Brett.C
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Post by Brett.C »

choco wrote:Years ago, the answer to all this was to use the original wishbone in reverse. The pivot point (the apex) solidly mounted to the centre of the axle and the other ends of the wishbones attached to the chassis rail.
When I read this I thought "that's scary" because the only thing stopping the axle from skewing sideways like a billy cart's steering is the spring. Surely there must have been more to this :shock:
Which has me thinking :idea: What if you were to fabricate a lower arm and attach it to the axle with a pivot?
Then use the split wishies as upper control rods. Of course they would have to be attached via a pivot above the axle on a sort of batwing. Then you would have what amounts to a triangulated four bar that would have good lateral control as well as looking reasonably "traditional."
The only problem I see is with the propensity of beam axles to bend for and aft.
Don't believe me. Next time you see a rod fitted with one that has the parkbrake on give one of the tires a kick so as to roll it backwards and watch the axle go "boing."
(BTW be sure to ask the owner first or you may end up with a smack in the gob for your troubles :D )
Maybe this type of setup would work best with a tube axle.

Still, I like Peter's suggestion about using a swivel in the middle of the axle like Rover used.
Anyone had any more thoughts along these lines?
I've been thinking :idea: What if you were to use a center pivot rack like a Camira? For lateral control you could use two center pivoted panhard rods that were attached on either side to the wishbones. This should keep bump steer to a minimum. I think this would work best on a suicide FE where there was minimal axle drop and you could hide the swivel behind the number plate bracket.

But this all seems like a lot of stuffing around just to retain a set of split wishies. Better off IMO to consign them to histories dustbin and use a fourbar or better still IFS.
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choco
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Post by choco »

To all yopu guys who can't see how the reverse wishbone would work, well, I agree. But I know there was more to it, as the axle could certainly NOT be located by the centre pivot alone. Relying on the spring to stop it moving around wouldn't work. There was something else, something pretty simple that just "worked" and it was used many years ago on a number of cars. Still, split bones were also used on a number of cars, my T Bucket included, and no way would I use that setup again!
I think Snooze knows what I am talking about.
Hey, Bill! WAKE UP!
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choper

Post by choper »

Bret... IFS on a Hot Rod? bite your tongue:-) - only stirring. Everyone has their own thoughts on what works for them. But back on to the subject of split wishbones, it's a mute point for David, as they won't accept them in Qld. And to my understanding the ban on split wishbones and hairpins in QLD comes from within the street rodding community, and that's a bad thing.
Do split wishbones work?Ask the thousands of rodders that used them without any problems in the past. I've never came across any suspension failure that can be attributed to split wishbones, but maybe you have some horror stories. And I suppose we can't discount backyard agricultural repair attempts. For those that are afraid that the axle will fail due to twisting, why do many manufacturers still use coil springs that are constantly twisted as the suspension arms travel up and down? Ring Kents Engineering or any truck suspension workshop and ask them what they feel about Henrys axles... some have axles on display that are twisted like a pretzel without any evidence of fatigue, and they would tell you that they can reinstate that axle to full workable condition. I seem to remember that someone in the states has an axle mounted on the wall tied in a knot!
Any argument can be twisted (pun intended) to arrive to a foregone conclusion, you only have to listen to politicians rave on, but the truth isn't always as simple as black and white.
Quite a few cars passed stringent engineering checks these last few years in Victoria for full rego with front hairpins (which duplicates split wishbones) these engineers were putting their future on the line in the belief that these suspensions are NOT unsafe.
Fair enough if you don't think this setup will work or if you don't like it, but I think we have to be careful how we approach some of what could be termed controversial subjects in the public forum, firstly in case we give the wrong impression to anybody looking for information, but more importantly... who knows who's lurkin out there that could use some of this information as ammunition to further restrict our ability to enjoy our hobby. We don't want some bureaucrat taking on the mantle to save us from ourselves thus banning split 'bones and hairpins.
Later
Chopper
Brett.C
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Post by Brett.C »

Bret... IFS on a Hot Rod? bite your tongue
Steady on. I've been biting my tongue so much that there's not much of it left to bite on :lol:
it's a mute point for David, as they won't accept them in Qld.
Yes and I think it would be difficult he in NSW as well. No way for limited rego (or nor more than 12" apart) and you'd have to get an engineer to approve it for full rego. And our most "friendly" engineer recently passed away :cry:
Be interested to see what what's in the National Guidelines.
who knows who's lurkin out there that could use some of this information as ammunition to further restrict our ability to enjoy our hobby
What :shock: With all those references to bar stools, rovers, pugs and billy carts
I don't think they'd even know what we're on about.
Come to think of it we don't either :?
David

Post by David »

I wont be going with split bones now any way, i want to drive my rod every where and have my kid in it so i am seriously looking at going for the modern look and running ifs, but I need to find out the costs involved before I'm sure. Thanks again for all the help guys.
Dave.
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Post by Guest »

At first reading, I was reminded of the old '30's Hudson system with a beam axle with two pivots, sort of an early attempt at independant suspension on the cheap. I am not sure how it worked, only having sen some illustrations. I also hear quite a few owners welded the pivots up so they had a more conventional solid axle.

When you think about it the longitudinalleaf springs were very effective at what they did, considering how early they were invented, how long they have survived and how many complex functions they perform.
I am a bit of a fan of big Rods with front leaves and a dropped axle. Looks simple and effective.

As for transverse leaf springs, if you want to use a light weight unit, the boxy Vauxhall Viva's used a transverse leaf as the lower control arms with an A arm at the top (I think). They used a front-mounted rack though.

I read in an early Custom Rodder (or something: I was very young in those days) wherein they were suggesting to avoid twisting a tube axle, one radius arm (or hairpin, or 4-bar mount) was sleeved around the axle. The axle's castor was controlled by one side's radius arm only. The other held the axle in position "for and aft" only. Then you use coil overs and a panhard rod. Neat and simple.
PeterR

THIS TOPIC

Post by PeterR »

First to peddro, I accept your comment that it is inappropriate to criticise the driver of a poorly engineered vehicle when really the comments should be confined to the engineering itself.

Next, I suspect some of those rejecting the sound advice offered by a number of contributors have not read through the thread in its entirety. The text critical of split wishbones has been confined to axles with high torsional stiffness such as tube axles. There is nothing wrong with hairpins, split wishbones or rigid radius arms used in conjunction with axles designed to twist, and as I indicated earlier this arrangement is common practice on the rear suspension of contemporary vehicles.

The only reservation I expressed was the wisdom of exposing 60-year-old metal of unknown heritage to severe cyclic stresses, and yes that is just a personal opinion.

To Choper, I must disagree with your philosophy of not discussing controversial topics regarding matters of engineering practice because it may attract unwanted attention. There is a widely held perception by the community at large and within parts of the governing authorities that all rods by their nature are unsafe and their driver's irresponsible rev heads. The greatest contribution this forum can make to dispel this perception is to demonstrate there is a pool of sound knowledge available to constructors who put their hand up for guidance, and there is no holding back on the condemnation of unsound practices. To say nothing is to be interpreted as endorsement.
PeterR

REVERSED WISHBONES

Post by PeterR »

I suspect bcal is right on the money with his interpretation of the way the reversed wishbone may have been set up. The reversed wishbone would provide excellent transverse location with low roll centre, the split wishbones adequate front/rear location, and the difference in height between the pivot points at the axle the required resistance to braking torque. A further feature of such an arrangement is that it does not induce twist in the axle when one wheel negotiates a bump.

However, his comments on the for-aft flexing of the axle are also valid. Remember the lower pivot carries the majority of the braking forces, and this combined with the low bending stiffness of an I beam axle in the horizontal plane means the tyre patch will move backwards under heavy braking and could result in chatter on an uneven surface.

As a tube axle has equal bending stiffness in both planes along with excellent torsional stiffness it would be an ideal candidate for this arrangement.
Guest

Post by Guest »

Does anyone know if the SuperBell and Magnum dropped axles - which are cast and not forged like Henry's originals - react to twisting forces in the same way as the originals? I assume cheapness of manufacture is the reason theyre now cast not forged. Any reports of them failing? I know theyre sold in their thousands but then asbestos sheeting was too....
Brett.C
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Post by Brett.C »

I read in an early Custom Rodder (or something: I was very young in those days) wherein they were suggesting to avoid twisting a tube axle, one radius arm (or hairpin, or 4-bar mount) was sleeved around the axle. The axle's castor was controlled by one side's radius arm only. The other held the axle in position "for and aft" only. Then you use coil overs and a panhard rod. Neat and simple.
Hmmm.
I like that idea.
Nice n simple.
I wonder if you could make a simple clevis type bracket that bolted to the perch mount. Then you could fix a pivot on the end of the radius rod and bolt it into the clevis. That way you could run the transverse spring without the need for a panhard rod. Tho I'd keep the panhard rod.
And you would obviously need a ball socket on the ends of the rods.

choper wrote:And to my understanding the ban on split wishbones and hairpins in QLD comes from within the street rodding community, and that's a bad thing.
Maybe the people with a vested interest in 4 bar systems did too good a job in pointing out to us the pitfalls of these setups.
choper

Post by choper »

Hey Peter, you are quite correct that we need not withdraw from controversial discussions, especially if it's beneficial to us in understanding how to improve our hobby, or why others have differing opinions, but I still would be hesitant in leaving ourselves open to scrutiny by registration authorities especially in an area as gray as we have been discussing. I'd hate to see someone ban split wishbones because they perceive that they are dangerous, and I don't think that anyone has proven the point that they are indeed dangerous. If we had to live in a perfect world, we wouldn't be living at all.
As to how the community perceives street rodding as a whole, I haven't in recent times come across the opinion that we are an irresponsible rabble, those times are long gone.
In regards to the question about SuperBell and Magnum cast axles, although they can be twisted to a certain degree (improved casting and material advances apparently can mean that they can perform better in that respect) they will not perform the same as the original forged axles. Of course Chassis Engineering axles are forged, and Magnum were going to have them forged as well, but as far as I know it hasn't happened as yet.
PeterR

SLEEVED ARM

Post by PeterR »

I read in an early Custom Rodder (or something: I was very young in those days) wherein they were suggesting to avoid twisting a tube axle, one radius arm (or hairpin, or 4-bar mount) was sleeved around the axle. The axle's castor was controlled by one side's radius arm only. The other held the axle in position "for and aft" only. Then you use coil overs and a panhard rod. Neat and simple.
There is one problem with this configuration. The brake torque reaction is carried only by the arm that is fixed to the axle. The arm then applies an upward force at the chassis pivot point, and this in turn means there is an increased load carried by the tyre on that side and a corresponding reduction of load carried by the tyre on the other side of the car. The net result is premature lockup under braking of the wheel on the sleeved side.

Now, here is a question for you all to contemplate. How can an arrangement such as this be used to advantage on a live rear end.
Brett.C
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Post by Brett.C »

Now, here is a question for you all to contemplate. How can an arrangement such as this be used to advantage on a live rear end.
Hmmm.
If the fixed rod was on the left and the slipper on the right.
Then under acceleration the torque forces in the diff will cause the left side on the vehicle to rise thereby putting more weight on the right and thus adding more traction to the right wheel.
A form of traction control, but not easy to tune. An adjustable three link system would be better.
Like the front, it too would be susceptible to axle tramp under braking but not as pronounced because there are less baking forces on the rear. Could this not be somewhat alleviated by the use of a horizontally mounted shock absorber on the slipper side?
But now we're delving back into the ugly :roll:
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