Ok  - I'm at work and the tables are right here - at a (conservative) 33,000 psi "proof load" for the 5/16 coarse threaded rod, its good for (.0524 x 33000 x .75) = about 1300 pounds axial pull. That using 75% of proof strength for safety sake. No worries with this unless you leave it loose and pound on it like a slide hammer. SAE grade 5 material jumps this to (.0524 x 85000 x .75 = 3,340 lbs allowable and SAE Grade 8 to (.0524 x120000 x .75) = 4,700 lbs.

The weakest link looks like the male thread of the rod-end being placed in a bending situation - not good. Better design would be SAE Grade 8 threaded "stud" (all-thread / cut off bolt / whatever) tightened into the internally threaded bar (for 5/8 inch depth - two times the nominal diameter) and using a female threaded rod end. Fit thick washer between the rod end and the bar - and grind it (thinner) until the rod end tightens securely and stops turning - exactly where it needs to be pointed. 

If this doesn't work - get a chain........ 

 
 Steve Metzger       Tucson, Arizona

I am most concerned about the bending moment of the outrigger welded to the header flange. Looks like all of the torque load is transmitted through about a 5/8 or so stand off about 6 or so inches long. It sure looks as this stand off will bend and or distort the headder flange with any serious torque load.

I am not saying this ain't gonna break some day-maybe soon. But here is some more info on what it is.



The standoff you write of, Don is about 3" long, not 6". I was able to shorten mine some to get the rod to lean over more away from some other stuff below.

For my money it seems like an additional safety chain or turnbuckle link would solve the question. And I might add, I am no engineer, but this setup has been working pretty well-time will tell, I've got my fingers crossed.



If it's a stick car or of course a race car, there is gonna be more load - on everything. So on the headers you could always modify this part or start over and build your own.

Like I said somewhere else, I was skeptical, and discussed it with the manufacturer. I am not a salesman for the FPT.

You also have to keep assume that the rods and nuts are taunt. No rock and roll. This is a bad thing even on a stock tbird if not looked after and disaster can happen. With no slack in them there is less inertia.

       A  L  A  N   F  R  A  K  E  S   ~  Tulsa, OK    

I usually have my guys design little round bars welded on like that as if the fillet weld on the end is a tube.......so it would be a tube .75 diameter OD and .625 ID - .060 wall.

Section modulus is .135 (a measure of bending stiffness)

Moment arm (leverage) is 6 inches - load is 400 pounds maybe? How far from the rod eye to the crank centerline? Assume one side is loose? Many unknowns here.

Stress in the weld (6 x 400) ÷ .135 =17,800 psi 

17.8 ksi is less than the yielding strength of a MIG weld - this is a higher stress than I allow on the mining machines - but they run 24/7 all of the time. Usually on a weld of this type I insist on max stress of 7500 psi.

Its beer thirty isn't it?

 
 Steve Metzger       Tucson, Arizona

The design is probably OK but it seems a bit questionable.

The constant loading under part or full throttle is probably ok but the impact loading during shifting is really questionable. As you have had no problems I'll shelve my concerns.

I think the offset, rod end style restraint is an excellent "out of the box" solution to the header clearance issues in the T-bird. After I saw this I immediately started daydreaming about using an "angle-milled" plate under a pair of "rams horns" (to turn them in toward the block a bit) with this sort of set-up welded onto the spacers. Anyway........

I don't agree with the size of the restraint bar - and the use of the male threaded rod end. Impact can increase any of the stresses we figure by a factor of three (or more) at any time. If the bar were increased to 3/4 diameter, fillet weld increased to 1/8 of throat, and the rod end mounted in a different manner, you could pound on it with a little less mercy.....which is usually what racers do!

There is another way of mounting, with a female rod end - to clamp it to the welded stub with a Grade 8 capscrew through the ball (using a taper on the end of the stub for angular clearance). That way the rod end is axially loaded (as they are intended to be) down towards the frame mount. At the frame eyelet a set of the polyurethane biscuits used on a sway bar link would be just right......  

 
 Steve Metzger       Tucson, Arizona

Also transmits all the vibration directly through the link to the frame. Makes the rubber in the motor mounts useless. The rod end would be better utilized turned 90 degrees. They are not designed for any stress's in this direction.

      Steve, Notice he said it's embedded into the header flange. If the joint in the flange is tight, then it's all a bending force at the face of the flange and really is a solid bar. The weld is not really structural.

  It's five o'clock somewhere!

Frank/Rebop

Bristol, In ( by Elkhart) 

I agree the rod end is being used incorrectly. I intended to machine up a Y for the vertical rod, but I still have a serious concern about the bending moment on the header flange. This could be adressed to some extent by using a larger outrigger footprint.

As the welding demonstration artist asked after welding cast Iron,  "Alright folks what do you want to see welded"? My cousin with out missing a beat said Aluminum to Oak.

Don:

That's a good one.  Back in the earliest days of Hot Rod Magazine, one of the writers, trying to brag about a welder's skill, said he could "weld a glass rod to a toilet seat".

Another story.  When I was working in auto repair about 40 years ago, someone brought an exhaust manifold in with a twisted off stud.  I drilled a pilot hole through the stud, then took my cutting torch and burned out the steel stud, leaving the cast iron intact.  An old guy walked over and looked at the manifold, then said, "I'll be damned.  First time I ever saw anyone cut threads with a torch".  I never told him any differently.

John

John - "The Hoosier Hurricane"

Where does the stock steady rest mount?


Lawrenceville, GA