Hot Rods broken radius rods?? why??help!!!

hi all. well I keep braking my rear radius rods on my 1934 closed cab, its running the stock rear suspension shocks etc banjo diff, just lowered heaps and the radius rods are bolted directly to the diff and then welded to the mounts as well the rods have been split and connect to the ch***is via adjustable rose joints, the radius rods are snapping in front of the bolt on mounts of the diff. the only thing I can think of for why this maybe happening is that there should be a pivot point at this mount as diff movement flex is transferring on to the radius rods and its got no give. I've tried looking for rear end hair pin radius rods set up on the net and cant find anything to compare to, I thought I was getting front axle hop but now I think it was the rear getting out of shape shimming from axle bind up?? any suggestions on information on rear end set ups and diagrams would be great

 

A picture sure would help

 

If the radius rods are spit and attached to the frame rails (or close to them width wise) that is your problem. As the ch***is tries to roll on the suspension it is trying to raise one attachment point and lower the other. As the axle housing can't twist the radius rods are put in a bind and subsequently they bend or break. If the rod attachment points are close together and use mounting bushings with some sort of compliance rather than the rose (heim) joints the problem should go away.
Beefy radius rods may stop the breakage with your current set up but without the ability for the ch***is to roll on the suspension handling and driveability will be compromised.
Mounting one of the radius rods on a sleeve that can rotate on the housing will also tend to fix the problem but then you are relying on a single radius rod to control the torque forces on the rear end unless you are still running a torque tube style driveline.
Any easy visual on this is to watch "door" style cars at the drags. The ladder bar (basically what you have) cars lift both front wheels equally apart from any rotation induced by tire squat while the four link cars have a tendency to rotate and lift the left front unless they have a stout anti roll bar. You don't have enough torque or traction to make your car rotate on the longitudinal axis but the forces induced by turning corners are enough to break the split wishbones which were not designed to carry that sort of load. In the original application they are meant to provide longitudinal location of the ends of the axle housing while the torque tube does what its name implies and controls torque reaction.

Roo

 

What is the rear suspension type? Did you split the rear bones or are they true radius rods? If they are radius rods, 3 link or 4 link? Triangulated or parallel? Why not convert to parallel leaf springs? Pictures would have answered all these questions.

 

Exactly as Roo said.

 

Did you remove the original torque tube ? And not add something to take the place of its main function ?

 

If you still have the closed drive shaft, the split radius rods will bind up when one wheel hits a bump. Also, they have to pivot at the front end exactly in line with the U joint or they will bind and break. If you have converted to open drive, you are asking too much of the radius rods to act as traction bars, they just aren't strong enough.

 

Roo, What are you doing up this early? Running the Mini today?

 

ok im uploading photos to my albums so you all can see.

Roo your dead right that was my line of thinking,
the radius rods need to pivot at the mount on the frame (as they are now) but also at the diff which they don't, I've been wondering also as its a open shaft (being a closed cab) not a torque tube enclosed tail shaft,
what's stoping the diff from rotating under acceleration??
the tubes that's what, and having them being rose jointed at both ends tells me the only way would be a four bar link,
the tubes radius rods from what ive been told from the guy in the states that built the car is that there the original ones been shortened and mounted to the underside of the frame.
also is there any links or information on specs to build or buy and replace these radius rods with a system that actually works as this is my every day drive and needs to be right.

 

having trouble uploading the pics. I couldn't add them to this link so ive created a album called radius rods on my profile

 

http://www.jalopyjournal.com/forum/album.php?albumid=40015 a link to these photos

 

I also should add the radius rods are mounted to the outer , under side of the frame rails as you will no doubtable see in the photos on the link provided above.
buy the way this is how the car was built in the states I bought it here in oz got it p***ed and full rego in my state as it appeared to be original, ( I new it was modified and lowered etc and this is my first ever experience with this suspension set up)
so i'm just researching on what to do to make this original diff spring system work on the street give good handling and ride, yes I still like to go around corners as fast as this old girl will let me, hopefully I can make it work better then it was intended for.

 

Your problem is two fold and in need of redesign.

Ladder bar type will help quite a bit, but only 1/2 of your problem.
You can fashion a ladder bar with the original bones as the lower leg of the bar.


There's loads of info and debate on this type of set up and warnings of the design you currently have. Sorry if fell on deaf ears.
Something needs to flex in that setup and nothing will so it breaks. However bringing the forward mounting points of the bars to the center of the car pretty much solves the other issue.

Ladder bars and triangulated mounting can cause floor space issues on lowered rigs.


Pete & jakes has a good design for their rear ladder bars.
Take a look and try to ***imilate that concept.

 

hummmmmmmmmm...........I wont say a thing!

 

The Pete and Jakes catalog is loading really slow on my computer so here is a link to the parts at Honest Charlie's.

http://www.honestcharley.com/manufacturers/pete-jake-s/ch***is-parts/rear-ladder-bars.html

Roo

 

Don't blame the OP--someone on this side of the planet built the car and then it somehow got through the registration system in Australia which normally picks up poor engineering like this.

Roo

 

Roo explained it well. To sum it up, your set up is equal to a giant sway bar.

 

Here are some pics, no third link/torque arm and the mounts at the axle are too small, not enough spread/triangulation to deal with torque rotation. With a third link the setup could work, although marginal at best with the bones mounted out at the rails.

To the OP, there are many threads here on this discussion, a re-design is needed.

 

Then why post ?
And posting to say "I won't say a thing" is saying something although its not somehow helpful .

 

Your setup would only work if you had zero or nearly zero travel in your rear suspension.To much torsional stress being put on your rods.IMHO
I split my rear rods 300mm(all you are legally allowed to here)and beefed up the rods
ladder bar style,having a smaller dia top tube that bolted to the top of the diff housing above the original mounts.The front of the tube was welded to the top of the radius rods almost right up the front where the tierod ends where mounted to the ch***is,with gussets welded in at 300mm spacing along the length of them.
Many miles on both seal and gravel roads with no problems.Like said before,plenty of discussion and views on here about this subject.

 

Agreed. See the spread at the axle of the Honest Charlie's bars - or anyone else's.

Also, don't use tie rod ends at the forward mount.

 

+1 It won't work as is and breaks the rods because it is always putting them in a bind.

 

FWIW

Many cars are built this way because it seems the easiest, although not necessarly safe.

Refer to Pete and Jakes catalog fot hteir explaination.

The easiest way I can explain is:

1) take a piece of wire, bent it in a u shape with square 90 degree corners. Lay it on a flat surface and pick up one corner. Results, either the same side leg will come up the same or the opposite 90 degrede corner. Represents critical bind and one corner will break if continued stress iis endured.

2) now bend in the shape of a triangle, with roughly even sides. Pick up one of the corners. Results, the other 2 sides will continue to lay flat. Representing no of minimal bind.

This is the cause of my using 4 bar suspenssion with transverse spring approximately 30 years ago. There is even bind in this example because the parallel 4 bar in their arc will result in the axle moving a small amount back and forward.

The other, problem I see in the subject vehicle, the radius rods are expected to be torque arms as well a radius rods.

My suggestion would be to (at the very lest) place a second rod/bar on the top to control the attempted rotation of the rear axle and mount the forward ends at a common mount wi some rotational ability.

Best of luck, hope this is helpful.

understand, I am in no way an engineer.

Search this site for "4 Links" for some very good discussion.

Jack

 

thanks all for your input and help, like ive always said if you want to do it right you have to build it your self. im really amazed how this suspension has lasted but after reading and researching ive learnt a lot and all though this car presented very well I new I would have to do a lot to get it right. its all part of the learning curve, im really sure my steering and the front end needs attension as well. but ill sort this back end out and then ill rebuild the front end steering, since owning the car a few months ive put two new water pumps a torque starter elec dizzy head gaskets and soon to put adjustiable lifters in, buy the time ive finished I will have rebuilt the car. then it will be right, the difference it didn't come in boxes but as a fully ***embled car.i think ill stick with buying them in boxes. lol
but its all part of the journey and ive got a hotrod. soon to be a lot hotter then I when I got it,
again though I appreciate all import and views, feel free to hook me up with any plans on rear end design that has the traditional look.
oh and buy the way this was a HAMB registed rod theres a outline on the firewall from the hamb plate

 

Simply relocate the frame mounts toward the center.

Split wishbones spread out to the perimeter frame are not meant for driveways & street use, it's for the SaltFlats.

 

The great thing about these broken suspension posts is that over time the "traditional" **** designs all break, and eventually everyone learns about correct geometry. Be careful driving!

 

Greetings

FWIW, I attended the Southwest Nationals at Okla City, this past week end and low and behold, a fellow driving a model A, had the front torn apart replacing a broken perch bolt. A serious accident had not happened.

The perch bolt had snapped at the joint where the (tube) axle and the bottom where the radius rods meet.

The logical problem was the amount of stress with split radius rods and tube axle.

Can't say I like using radius rods and I beam axle but supposedly the I beam axle will twist reducing the stress of moving the pivot point out to the frame width.

 

I bet your jam nut on those tie rod ends backs off all the time as well. bottomline is you need to redo your rear suspension setup before someone gets hurt.

 

Mate rooman and the others that are saying move your radius rods towards the centre of the car are onto it.

Worth noting that UNDER THE NATIONAL STREET ROD GUIDLINES IN AUSTRALIA the recommendation is that you can split radius rods but suggest by no more that 300 apart from the centre line.

That goes some way to solving the problem.

There are some threads on HAMB aboult putting an extra bushed torque arm on on top of the diff to help prevent forward twist of the diff and reduct the load on the radius rods.

Hope you get it sorted soon looks to be a cool ride

Cheers

 

Are 34 rear radius rods really upto the task of being split and still able to perform any ways???