Sooo...you still want to split your rear wishbone??

The forever argued and usually hostile discussion of splitting your rear wishbones to the outer frame still exists today!!

I never really had a problem with mine, performance and handling wise. My suspension travel was kinda low but my **** can handle it!

Well, after reading countless threads here and over at the barn about proper ch***is set up and other tid bits I still couldnt wrap my head around what was such a big deal...

I would tend to imagine if this had gone unnoticed it could be a big deal!







Since I only have a few more weeks of driving before the weather turns us into snowmen, I gave it a quick fix at best. Ground, drilled, and welded the crack then fishplated over it.
It will be reengineered this winter.




I thought I would post this to show that the arms will crack!! Many of the other threads had guys talking about how they could crack...so heres the evidence!

 

Yep, it sure can happen. Mine actually bent beyond belief. Glad you, or anyone else, were not injured. What kind of front mounts are you running on the front end of those bones?

 

tie rod end style on a plate to the outer frame rail.

 

Torque arm???

 

Torque arm would not have helped, as it would just break something else.

The torque is not causing the entire problem, it's also the problem of what gets stressed when one wheel moves up or down, opposite of the other wheel.

If you beef everything up like a battleship, then the rear axle tubes will crack and break. There are pics of that on hamb, on a T bucket.

 

We found the same thing on our race car. One month before Bonneville we had to construct new split radius rods. We chose to use heavy 32 fronts to make our new rears. Which became a big deal because of the brackets to the rear backing plates, we decided to make them stronger using 1/2" plate and picking up three bolt holes instead of only two. We also reinforced the full length of the bars. That tells you we were concerned with our safety. If you split the rears, be sure and inspect them on a regular basis.--TV We run ours to the center with Heim joints, so it should work ok, but we still had a problem. We also installed a panard bar like we have in the front.

 

The reason split wishbone on the rear is asking for trouble is because you effectively are making the rearend housing into a very large anti-roll bar. Add into this the torque reaction if the rods are the only thing connecting the rearend that provide twisting resistance form the torque. It has to give somewhere and the radius rods bend. Over time, it creates a fatigue crack. Glad you found out before it broke completely.

 

Like a lot of things, there can be a number of factors involved. Age of the metal, bad metal, bad engineering, etc.

 

Truthfully ford rear bones aint the strongest either, i'm running semi-split, '40 fronts on the rear of my roadster

 

Is there really a way to engineer split rear wishbones?
Other than adding a bush to one mounting point on each rear mount
or mounting your diff rigid there does'nt seem to be an adequate solution.
Front rubber bushes might help for a while but as said when one side travels up or down stress is caused either way.
Shoot me down if I'm wrong,I don't know f-all.

 

I'm no expert but in my opinion...

Technically if the pivot of the wishbone is the same place as the torque tube in height and forward, then you should be almost perfect. the only issue then is body lean causing things to twist

 

Triangulate them. Front wishbone-style. Anything else will stress something, somewhere, every time you go round a corner or over a bump.

 

Technically you are correct to a point, but when using an open driveline, the wishbones, in addition to locating the rear axle, are now handling all of the torque, or upward motion of the pinion which was originally controlled by the rigid torque tube.
The attached pictures ('40 Ford wishbones) show what can happen.

 

well. Looks like im gonna be using hairpins on mine.

 

If you run them out on the rails you'll have the exact same problem....eventually. It's not about the material used or the design of the arms (split bones or hairpins). It's about the simple engineering principles involved.

This will probably turn into another one of those argumentative threads but you just have to accept that your rear housing and / or your radius rod are just not supposed to flex.

Thanks for letting people know about this safety issue again Slick Willy.

Pete

 

If you want the look of split bones, mount them so each end can pivot and articulate......by each end, I mean at the frame mounting position, and at the axle. Then add pivoting triangulated rods inboard to handle the torque issue. Basically a triangulated 4-link setup, but with bones for the lower rods.

 

zzzzackly!

 

I plan on using a 46 open drive truck banjo 4 door av8,so if I triangulate a fabbed hairpin setup will heims at the front suffice?Or should I have all 3 points each side.

 

Correct, this puts the lower bones in compression only under acceleration and also they do not see the twisting load from the rear housing acting like a sway bar.

 

****gy is correct about the front of the bone being in alignment with the rear of the ******/ujoint of you are running an open driveline or the pivot point on the torque tube if you are running a torque tube.

One factor that is probably comming into play is the age of the bones. we have to remember that split bones on a ford 50 years ago is not the same as splitting the same bones today.

There is one thing that may also be taken into account. the fellas that did it when I was a kid and trying to throw some meat at them used to add rods that were triangulated to them made it look like an early ladder bar. That strengthened them quite a bit. I wish I had a picture. I'll try and conjure up a quick drawing to show what I am talking about.

be back in a flash.

OK pretty ****py drawing but it gives you a general idea right?

 

i had no clue there was a issue to be had here iv seen so many split bones.. i like the look.. and planing on building a bobtail traditinal T.. i have 40s bones for the front i beam axle.. and am going to use a 9" rear... and was not sure what to use for the bones for the rear to finish the look.. but this is def something to take into consideration.. as i want to build something that is safe fist and for most looks come second.
chris.

 

Think of the old rule of thumb that split wishbones and hairpins will work on an I-beam axle because it will allow some twisting motion. If you throw a tube axle into the mix, things will break because the rigid tube axle will not twist.
Now take this and apply it to the rear of the car...an axle housing wont twist...
There was a sketch in a magazine a while back showing an I beam with one of the bones rotated slightly up and the other down which clearly illustrated the twisting motion, wish I could find it!

 

You can do it like a Camero. Run your split bones but put joints at both ends. Run a torque arm next to the drive shaft. Put a shackel at the front so the arcs don't fight. I like about a 33" arm. I have run the equivalent of this set up since 64. The first arm I used was from a 50 Olds and put under a Chevy II.

 

thanks for the advice.. i can visualize this.
chris.

 

Thanks Chris, I used to drag race the Chevy II pretty hard and I have never had a problem with this design in any of the cars I used it under.

 

Heres mine. It was mentioned earlier. Planning on a 3 link set up. Waiting for parts, progress is halted.

 

Ok. Good thread.

I am getting ready to set up my '39 banjo converted to open drive. I was planning on using the stock long rear radius rods and tie it in at the front of the rods like the original torque tube with a bolt thru but attached to a crossmember. Then add a torque rod.
This sound Ok?

 

This is how the "Hot Rod Works" does it...

Radius rod mounting... Torque arm mounting...

 

That's my plan!

Thanks