Split wishbones/open drive+Torque Arm= NECESSITY!!!

Just a little note to all those that split the rear wishbones and remove the torque tube...

USE A TORQUE ARM!!!

I was at Limeworks yesterday and saw some really nice chrome split wishbones that didn't look right to me. Upon further inspection, one arm was tweeked and the other was cracked right through the casting where it mounts to the rear. I really didn't think too much about it but then Steve brought me a picture of the same wishbones and said:

"See this?... This is what happens when you split the rear bones and don't use a torque arm."

Then he walked away and I picked up what I came for and went home.

This morning I woke up thinking about those bones...

That was one nasty looking break and it could have been dissasterous. I don't think anyone was hurt but it sure could have happened...

I've always heard that you shouldn't run an open rear with split bones by themselves but I'd always sort of thought of it as just a "something could happen" type thing and not a "will happen" issue.

But now I've had it graphically driven home...
Don't do it.

Another thing that came up was that Steve said that since the bones were chrome, it would be easier to see defects and catch crack before they get serious.

I think a non-show chrome job will be in my suspension parts future...

Something to think about.

 

Just got off the phone with Craig out there, I like ordering from those guys

A. Example of a Torque arm.

 

I had too much coffee this morning and titled this thing in a way that NOBODY would have any idea what I was on about without opening the damn thread...

That's one of my HAMB-peeves...

So I changed the title...

Tman..

Craig is great isn't he? I never know what the hell I need untill it's too late to reasonably expect to get it in time for when I NEED it...

Craig has always gotten it to me in time.

 

EVERYONE at Limeworks is great to deal with! I did a post a while back about the GOOD companies out there, Limeworks was one of the first that came to mind.

 

if improperly compensated for the chome job itself could also contribute to the bones early demise, the bones should be put on a slow simmer at 500 degrees untill hydrogen levels are brought to an acceptible level..

or so I've heard

 

New and ignorant 'FNG'.......... What purpose does this torque bar serve (ignorant, OK)? Seem if the rear end is under power, it will want to rotate along the 'axle axis. Does this torque rod serve a job I ain't seein'? I am buildin' a '33 pickup currently, and wish to use the stock buggy spring setup, and original style rear end wishbones.
Input is what I'm lookin' for (sponge).
Thanks - BigKen

 

That TA in my pic is mounted several inches HIGHER in the rear that the bones are. It limits axle twist by being ABOVE the axle centerline.

FWIW, those rod ends are P&J Urethane versions, they are too soft, I can see them compressing, so I will turn some out of Nylatron on the lathe to replace them with.

 

Split wishbones are a TERRIBLE idea unless both the front and rear connections are allowed to swivel. In that case a torque arm of some kind is an absolute necessity. That torque arm must be free at the forward end to move forward, backward, and side to side to a small extent such as in a large rubber bushing. I prefer a double spherical rod end. A panhard bar is also required....unless you run a transverse spring with short shackles. I'd run the panhard in either case.

60'sStyle is correct about chrome. Unless a proper heat-treat is done after chroming, you have hydrogen embrittlement which probably added to the cracking situation in the original post about split-bones.

 

So it does aid in the torque/twist area, as the old ladder bars of the 60's? From the angle of the shot, the ends almost appear on the same plane. SO, if I am to use the original wishbone for the rear, it is highly recommended to use a bar such as this? How about a sway bar, also?

BigKen - FNG

 

here's a copy/paste of some talk concerning just this topic

sounds like the area of fracture in above example may have been of a more susceptible material..

......................................


Hydrogen gas is liberated at the cathode during various pretreatment and electroplating processes. This active hydrogen can embrittle both the chromium deposit, and the steel substrate whenever the workpiece is cathodic (i.e. attached to the negative pole of a direct current power supply). Certain steels are more susceptible to embrittlement than others. Typically, hardened or high strength steels are especially susceptible. Steels that have been heat treated to a hardness of Rockwell C45 or higher are often at greatest risk. Also, tensile stresses can be introduced into the case of the workpiece, prior to plating, by the various machining operations (grinding, polishing, etc.) that may be performed.

The problem can become so severe as to cause the complete failure of a part which has been placed in service and subjected to loads. Typically this occurs when the combined or compounded stresses from the substrate itself, and the pretreatment and plating processes reduce the fatigue strength of the plated part below its fatigue limit.

The tensile stress in the substrate can be normally be reduced, prior to plating, by heat-treatment techniques or shot peening. Peening can sometimes convert the unwanted tensile stress to a more desirable compressive stress.

After plating, parts which are susceptible to embrittlement are often subjected to a heat treatment (baking) procedure, called "hydrogen embrittlement relief". Often, a temperature of 375 deg. F for 3 or more hours is used. Sometimes, specifications require that the embrittlement relief bake be performed within a certain number of hours after plating. The process serves to remove or redistribute the hydrogen, but may further reduce the fatigue limit of high strength steels. This phenomenon was described by R.A.F. Hammond and C. Williams ("Metallurgical Reviews", 5, 165, 1960) and again by J.K. Dennis and T.E. Such ("Nickel and Chromium Plating - Second Edition", 1986, p.72).

To reduce the adverse effects of hydrogen embrittlement, you can consider whether or not the following concepts are pertinent or applicable to your situation: - Avoid or reduce pretreatment steps which can introduce hydrogen.
- Ensure the post-plate hydrogen embrittlement relief is effective.

 

The front of the bones and the TA are on the same plane, the rearr of the bones in 4" below the axle centerline and the TA is mounted ABove the axle centerline. Yes, it keeps the rear from twisting or wrapping up.

 

Here is another version.

http://www.hotrodworks.com/radiusrodmount.htm

 

That's not a good example. Those 'bones aren't split to the side....they come together at the center sorta like Henry designed it.

 

I asked that question and Steve said the Chroming was not an issue in this case...

 

Yes, but it shows the angle of the components better than in my pics. The TA still controlls axle twist like my setup.

 

W/o seeing the bones in question, I would bet that excessive cleanup/grinding of the welds in prep for chroming probably had a lot to do with it. I left the welds on my bones pretty much intact to avoid this issue.

 

Man, that nails it dead on. I've been in the engineering field for years, and that setup is exactly what I had mentally pictured.
Now, they (HotRod Works) say that works on '35-'40. Any reason this idea cannot be adapted to '33?
Gotta love it.

BigKen - FNG

 

you talkin' about 38Chevy454?

 

Does it make a diffrence,if the tourque arm is above, or below the axle centerline? I am using a 'torque link' from the top of the axle housing to a place on the frame,pivoting from both ends. Sparky

 

Above the axle centerline=tension
Below the axle centerline=compression

My wishbones are in compression under load while the TA is under tension.

I tried a short torquelink similar to what Sam has on the BFD, it was too short and the geometry got all goofy through the range of travel.

 

This was a break at a weld joint...

This was a break through the casting itself.

 

Goofy???

Was it binding because the TA and the wishbones were swinging different arcs?

In the picture you posted, it does look like the TA is barely above the axle centerline.....how far above is it???

I'm running (setup but not finished) split wishbones with heims in the front. I didn't split them so that they are 90 degrees to the axle though. They are also fairly short (3 feet), I'm not sure what year they came off of. I wasn't planning on running a TA because I figured that because of the way I mounted them (less than 90 deg....aka still some angle) the stress would be lower and the tires would slip or the weak ass banjo would break first (it's all stock 40 ford).

How many of you guys have bent/broken wishbones? How were they mounted?

In the stock application, the bones have no way to pivot when the axle rolls compared to the frame. They also have to handle the reaction torque to the axle (which is smaller with an 85 hp flatty granted). I dunno.....

 

No, the goofiness was with a short (approx8") torque link. It was just an experiment to see if it could be done. It actually made the pinion angle/rise WORSE as it went through the travel given the parameters.

That TA I have now works flawlessly, the bones are a good 6" lower in the rear than the TA. Triangluation!

 

It shouldn't be the distance between the bones and the TA, but the distance from the TA to the axle centerline. If you are trying to react to a torque on the axle the further distance from the centerline the less force on the rod. If you put a TA mounted on the centerline of the axle it would do nothing (maybe bind the suspension if it was a different length than the wishbone)....

 

Are the bones you are running mounted rigid to the axle or do you have a three link? maybe thats where I'm confused here....

 

Your header caught my attention I know that it is not polite to throw stones at other peoples work but after reviewing the pictures and reading the related posts I think that you have created a rear suspension that needs some revision. The pictures exhibit a potential problem related to the travel and location of the rear end. This will create a spooky handling ride when operating. Observations that I question are related to the rear control arms. It appears that they have two pivot points one at the front of the lower rods and one at the upper rod that may not swing in the same arc. On a simplistic radius rod application the rear end is in a fixed mount at the rear and a rotating front mount.. This sets the pinion angle, contols rear axle wrap and squares the rear end. Your lower arm design locates the rear but requires the addition of an additional arm which inturn makes this a 3 bar suspension. This approach is correct as it triangulates the radius rod to prevent them from bending and should revolve around the same axis. Your design follows some principles of a torque arm but not completely. Your upper bar only controls the wrap of the rear under acceleration and braking and estabishes a stable pinion angle. The small angle that is created has limited bearing on weight transfer therefore not actually acting as a torque arm more like an upper locating arm. Because of the concentated mounting area I am concerned about snaping the mounting studs during operation and you may mount the bracet higher on the pinion to balance out the lower arms. What this setup also fails to do is locate the rear end side to side. While you miight say that the buggy spring does this, remember the buggy spring is also on moveable points and as the spring flexes it actually changes dimension and position as the shackles pivot. This causes a sensation that the car is wandering as the body and rear end actually are moving on different planes and must be cured with the use of a panard rod, or watts link. If you want to get into this deeper there are a number of good books on chassis design that will help on the internet book stores. Your idea is ok it just needs a tune up, my immediate suggestion is to check that the bars all operate in the same arc maintaing pinion angle as well as eliminating twist in the rear spring main leaf during travel, add a panard rod and a provision for shock absorbers. happy motoring.

 

Blair, all THREE links have urethane rod ends on BOTH ends, yes, it is a 3 link and yes, the TA is far enough above the centerline to counteract the torque. Higher like the Hot rod Works TA would be even better but in this application, there wasnt any more room to spare under the floor. .

ElPolacko sells something very similar at Industrial Chassis.

 

Dick, I appreciate your comments and you do make some good points. This system works very well the way I have it, We have been using the word Torque Arm here as a descriptor. The car handles and launches great. The low CG of the car makes it handle like a slotcar (tops of doors are 32" from the ground).

No one hotrod is perfect, sure, I might tweak it a bit. A torsion style sway bar would be great but I havent really felt the need for it. Witht he minimal travel, the arcs are relatively even.

Back to Kilroys original post, split bones will bend! You need something to take the place of the old torque tube!

 

ah..........see I used to be completely comfortable with my rear setup but now you got me thinking.....maybe the bones won't be strong enough......but how many of you out there have had the split bones/transverse spring setup where the bones have failed? Isn't that how everyone did it in the old days?


I'm running stock type bones on a banjo, so they are solid mounted. Basically it's a simple control arm setup with a buggy spring. As I said before the bones aren't split 90 degrees like most, they form a triangle to help center the rear. I almost went to ladder bars but decided not to.....