Split wishbone suspension

David · Post by **David** » Thu Nov 13, 2003 10:50 am

The main reason i wanted to go with split wishbones was so that i could get the car sitting really low using a standard beam axle with the spring behind it, but apparently it isn't legal here on hot rod rego so I am going to look at a dropped axle and unsplit wishbone setup or the peugot if i can find one. I am probably going to go with a full roadster body now too.
Thanks for all the help.
Dave.

GBS · Post by **GBS** » Sun Nov 16, 2003 11:39 pm

Shiny wrote

If you are referring to my car about the 103.5" WB,my car is on deuce rails,106"WB.

I was not referring to your car Shiny. I had not seen the photo of yours when I wrote that entry. What I had in mind was the many rodders I have met over the years who have recessed the firewall to get a V8 into a stock wheelbase Model A and then complained about the lack of interior space and comfort on long trips. A Model A is small enough as is it is without having the engine intruding into your space.

old32 wrote

The car ìrockingî on the shackles causes this.

I knew that will cause the problem. The car I was referring to has a panhard bar and the rest of the front end is in excellent condition but it still changes direction. As I said before the owner claims that type of front end always does it but I donít agree.

bcal wrote

Another reason I've heard that they were used was because they increased roll stiffness on track cars.

You could be right there Brett. I remember the speedway midgets years ago used hair pins with tube axles and their front ends seemed to be very stiff. This might tie in with what Vern Tardel and Kent Fuller were saying about stiff suspensions that resisted turning.

Brian

Dave · Post by **Dave** » Tue Nov 18, 2003 12:27 pm

The latest project at the Castlemaine Rod Shop is using a split wishbone front end in an A model pickup utilising Ford truck Tie Rod ends. Take a look at their website http://www.rodshop.com.au/projectratrod.htm to see more. There is a good close up picture of the right hand side. (darn good photographer!). Maybe this is the sort of setup you could use?

GBS · Post by **GBS** » Tue Nov 18, 2003 11:58 pm

Dave

I can not follow Rodís reasoning behind the use of truck tie rod ends to prevent binding. There is nothing new about using these ends, they were the normal thing to use even back in the 1960s but it is not the pivot point that causes the binding, it is the fact that one end of the radius rod is not free to move up and down the same as the other end.

I know a lot of rodders use split rods but my point is, why use a spension that cannot move without bending a part (the axle) that is not a spring and is not designed to bend? That is simply not good engineering.

While looking at the picture of the radius rods, I could not help but notice the steering design. I may be wrong but I think this car will have a lot of bump steer. The drag link is mounted very high, so high it appears to be in line or slightly above the top of the end of the axle. As the suspension moves and the axle twists, the fore and aft movement of the top of the dropped end of the axle will be amplified by the height of the drop. This
movement will try and push the drag link back or pull it forward depending on whether the suspension is moving up or down. This will cause bump steer.

Brian

Brett.C · Post by **Brett.C** » Wed Nov 19, 2003 9:59 pm

GBS wrote:I can not follow Rodís reasoning behind the use of truck tie rod ends to prevent binding. There is nothing new about using these ends, they were the normal thing to use even back in the 1960s but it is not the pivot point that causes the binding, it is the fact that one end of the radius rod is not free to move up and down the same as the other end.

The truck tie rods were used because the car type ones would brake. Then the brackets had to be beefed up because they would also brake. Typical 60's heavy hammer engineering

And I think that's the point here. Obviously Rod would know better than most about the shortcomings of this setup but he's prepared to live with these compromises for the sake of the early look which is so popular these days.
But with all due respects to Rod, what else would you expect from a guy who sticks a 1000+HP aircraft engine in a car

I've driven a rod with a similar setup and I must admit I didn't like the way it wandered all over the road like a drunken sailor.
But then again it was no worse than a Hilux with a live front axle on semi elliptics.
IMO it all comes down to what puts a

on your face. (Providing what you're doing is safe of course).

Not too sure tho about the steering rod being parallel with the radius rod with a dropped axle. Didn't they use to hang the steering arm down so that the steering rod crossed over the radius rod? This meant that they traveled in a similar arc.

Nice rod tho. I'll be down that way next month so I'll have to stop by for a look if SWMBO will let me.

BTW Brian check your ppm inbox. I sent you those links you were asking me about.

Brootal · Post by **Brootal** » Wed Nov 19, 2003 10:44 pm

GBS wrote: ...but it is not the pivot point that causes the binding, it is the fact that one end of the radius rod is not free to move up and down the same as the other end.

I don't understand what you mean here Brian. Even an unsplit wishbone doesn't move the same at both ends. The rear joint pivots as the axle ends move up and down. Surely with split 'bones fitted with tie rod ends the same thing happens.

GBS wrote: I know a lot of rodders use split rods but my point is, why use a spension that cannot move without bending a part (the axle) that is not a spring and is not designed to bend? That is simply not good engineering.
Brian

From what I've read, early axles were MEANT to bend, as was the chassis etc. In effect, the axle and chassis were part of the suspension. It's only when people start boxing everything that the "suppleness" goes out of the frame and you end up with stress points due to some parts moving/flexing and others not.

Of course, if you wanted a perfect ride and great handling, you could always buy a NEW CAR! Ewwwww...

Choper · Post by **Choper** » Wed Nov 19, 2003 11:53 pm

You're right Brootal, there's no difference in regards to binding between split or unsplit wishbones. The forged axles Henry used were supposed to twist as part of the suspension, but stock wishbones would be the best system to use even above 4-bar set ups as you have a triangulated system that works with the axle and chassis. Split wishbones work as well as 4-bars with an original or repro forged axle, but don't use it or hairpins with cast or tube axles (although a lot of guys in the states go that way). Remember most hot rod suspensions would only have a 2" to 3" vertical travel, not enough to cause much of a twist.
As for how these suspensions work? I don't know what rods you guys that find the handling inferior rode in, there's plenty of split wishbone and hairpin equipped rods out there that work as good as any other suspension setups that you could come up with.

PeterR · Post by **PeterR** » Thu Nov 20, 2003 2:10 am

The behaviour of split wishbone is totally different to unsplit.

Unsplit
The wishbone and axle form a triangle with corners at the wishbone pivot and the two connection points to the axle. Just like a three-legged stool any corner can be lifted without inducing distortion in the structure. So, regardless of whether one or both wheels move and down, the plane of the triangle is not distorted and the axle is never twisted. Look under the rear of a NASCAR.

Split
The two pivot points along with the two connection points at the axle form a rectangle. Lifting one corner can only occur if something distorts, and in the case of a split bone suspension that is generally twisting of the axle. (Try and lift one leg of a four leg stool with the other three remaining on the ground). Open sections such as a C or I shape have little torsion resistance so the strain does not induce high internal stresses. However any person using a tube axle with split bones does so at their peril and is menace to others sharing the road.

For those who believe this is old technology just look under the rear of a modern front wheel drive car. A common arrangement is for a beam axle made of open C-section sheet steel restrained by a trailing arm at each end. The open C shape can twist to accommodate differential wheel heights and these give trouble free service. Though the radius arms are shorter than a split wishbone, functionally it is exactly the same. Some have the wheel stub mounted off the side of the arm between the chassis pivot and the cross "axle" to give rising camber rate but the result is still the same.

I still question the wisdom of using split bones on a forged axle. The history of the axle will be unknown and the constant twisting of a piece of 60-year-old steel is not my idea of sound engineering.

GBS · Post by **GBS** » Thu Nov 20, 2003 3:20 am

Brootal

I think Peter has explained the whole thing very well. What I was saying about each end of a split rod moving up and down the same amount is not what actually happens but rather what is trying to happen.

Look at the car from side on and picture it with a split rod but with the rear end of the rod disconnected from the chassis. As the wheel rises up over a bump the whole radius rod will lift up along its entire length because it is a solid rod and is bolted solidly to the axle.

Now picture the wheel going over the same bump but this time with the rod reconnected to the chassis. The rear end of the rod canít go up but the front end of it has to go with the wheel. The front end of the rod therefore rises in an arc and takes the axle with it. The axle must twist slightly because its opposite end is still being held in its normal position in a vice like grip by the other radius rod.

Peter is right about split rods not being good engineering. If you twist a piece of metal that is not designed to be twisted in that manner for long enough, sooner or later something is going to break.

Unfortunately what you see in ìtraditionalî rods is not always sound engineering practice and split wishbones is just one of them.

Another is the use 1935 Ford wire wheels on anything other that í35 Ford brake drums or custom built hubs or drums designed to support them.

The í35 drum was a heavy cast item with a ridge around the outside edge for the outer extremity of the wheel centre to fit on to. The drum added strength and support to the centre. If you use these wheels on another drum or hub that is not designed to provide this support you will eventually crack the centres.

In forty years in rodding I have only seen one warning in a rod magazine about this and that was in Street Rodder about three or four years ago.

If you are copying something from the past you have got to be careful.

Brian

Brootal · Post by **Brootal** » Thu Nov 20, 2003 9:34 am

Yep, that makes sense Brian. Thanks.

I guess (as Chopper said), the saving grace to an extent is that there isn't really that much travel in a solid axle suspension, but it still good insurance to check mounts and brackets etc regularly.

I'm a fan of the unsplit wishbone myself as I find it a neater look. Call me old fashioned.

Also, if you haven't read (or bought) Mike Bishop's "How to build a traditional A V8 roadster" you should. It has some very interesting facts about pros and cons of suspension setups.

choco · Post by **choco** » Thu Nov 20, 2003 10:29 am

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. The suspension geometry is maintained, there is plenty of room for the engine/transmission/sump and it was supposed to handle just as well as it was originally designed to. I saw this on a Model A roadster on 32 rails that was built in the 60's and owned by Roadsters of Port Adelaide member, Hans (something). He used to own Southern Radiators in Morphettville, SA. Some one out there might recognise the name. Anyway, this car was still registered 10 years ago and looked as good as any Hot Rod on the road that had just been finished. Hans said it handled like one of his Corvettes. I didn't notice the reversed wishbone until he pointed it out. He was doing some welding for me on my 36 Ford coupe to strengthen the rear pivot of the rear radius rods. He saw my split bones and told me how to fix it. I used them in their opriginal position but relaced the ball pivot with 2 rod ends which bolted to a bracket on the gearbox crossmember. The length of the brackets that the rod ends bolted to determined how much caster went into the front tube axle. I had suffered a great deal from bump steer, so Hans made the brackets a little longer and fixed the problem. However, he said that the reversed wishbone was a much better alternative.
Anyone else ever see this setup? It used to be quite popular (so Hans told me).

Brootal · Post by **Brootal** » Thu Nov 20, 2003 11:20 am

That sounds pretty interesting Choco. Can't say I've seen it, but then again, it's probably not something you'd notice unless pointed out to you. I just like all the pretty colours.

One thing I'm curious about though is, how is the wishbone mounted to the axle? It would obviously have to be located in the middle with some kind of bracket. One disadvantage would be the look. You wouldn't have that nice clean line of the axle, and we all know that looks ARE important.

peddro · Post by **peddro** » Thu Nov 20, 2003 11:51 am

Boris: are you implying that such things as HQ/L300 front ends are FREAKIN' UGLY?????

However any person using a tube axle with split bones does so at their peril and is menace to others sharing the road.

Forgive me if I'm wrong but doen't Ian Shaw's T tourer (which I believe has been on the road for a couple of decades) use this set-up??

What a prick he must be.........

Flatoz · Post by **Flatoz** » Thu Nov 20, 2003 12:05 pm

Recognise the name choco, mate use to work for him, as far as I know he still has his cars. I havent seen the roadster, but the old man has, I thougth he said that it was a 32?

choco · Post by **choco** » Thu Nov 20, 2003 1:54 pm

Flatoz wrote:Recognise the name choco, mate use to work for him, as far as I know he still has his cars. I havent seen the roadster, but the old man has, I thougth he said that it was a 32?

Yeah, you could be right, come to think or it. It had a 32 grille.

Boris, these setups look the part. I think the ball pivot cup is welded to the bottom of the axle and the wishbone ball sits in it like it's supposed to, only the other way around. Like I said before, you wouldn't know it was there unless it was pointed out. This car was pretty low to the ground, too. Had a SBC in it with triples and was a good runner, too.