Cloud9...68

Not sure if this adds anything to this discussion, and I am definitely not taking sides in the debate, but here is the set-up I bought directly from Karl four years ago:



He didn't recommend that I use his lower shock adapters (I didn't ask why), just that I torque the bolt to 150 lb-ft. The car gets serious abuse on a weekly basis on a track that includes a very large downhill turn where the car often gets airborne, with no issues so far. Have I just lucked out? But again, I'm sure Karl would have recommended that I purchase his lower shock adapters if he thought they would provide an extra margin of safety.

mj951

^^^ That looks solid.^^^
Who made the lower mount and what coil-over at you running?

Cloud9...68

Thanks. I'm running two-way adjustable Motor Clubsports. I bought the whole package, including the lower and upper mounts (along with two of pretty much everything else they sell) from Racers Edge, so I honestly don't know who made the mounts, I'm afraid.

mj951

2-way Moton Clubsports, thanks.
I have a few RE products and will consider Motons when I'm ready for full coil-overs.
Lots of good reviews i'm sure they're awesome. Also considering MCS's, Koni 3012 Rear's w/ rebuilt M030 double adjustable fronts.
Do you adjust them often? Between street and track? Between various tracks?
Did you consider a remote canister setup?

ninefiveone

ninefiveone

Cloud9...68

My Clubsports have remote canisters. As to whether I adjust them often, the background is actually a very long story, but the answer is no, I never adjust them. I hesitate to go into why, because I'm afraid it will unleash a long-winded back-and-forth delving into the darkest depths of suspension dynamics theory and practice, and the decision as to which is the "best" set-up has as many answers as there are practitioners. Let's just say my setup, in tandem with my ongoing education on the subject, is a work in progress. If you'd like the background, please PM me. Thanks.

Noahs944

I drank the 28mm VW T-Bar Kool-Aid too, thanks Spencer!

Droops83

Hey, I just went back and looked at your pictures and saw something that I somehow didn't notice before----in the above two pics of the broken stud, is that car fully resting on its wheels? If so, that means that the damper is at full droop, which in your case is obviously not enough (note the red helper spring is still compressed). The lower mounting eye of a fully extended damper should be at least an inch or two below the control arm mount when the car is at rest, which allows sufficient droop travel as the car traverses dips in the road. If the damper is running out of droop travel in this condition, then this will put undue strain on an already questionable mounting stud setup, even with a torsion bar/coil spring combination.

I would reach out to Lindsey Racing/Instax and show them the pics!

ninefiveone

@droops83: The car is not fully resting on it's wheels (no torsion bars so it can't). The driver side is being held up with jackstands and a race ramp. The driver side rear tire is just grazing the ground at the moment and I can pull the rear wheel off the car without lifting the car any higher.

MAGK944

951and944S

Yes, he does.
This guy has an animosity trigger so I knew he wouldn't listen to anything I would say, so I was just waiting it out to see if somebody else figured it out.

Now, yes, like I admitted, I'm blunt and to the point.
I introduce myself sometimes as an a$$hole.
My intent to keep ninefiveone from walking up the wrong alley was my sole reason for even entering this thread.
This bothered me so much that I contacted Intrax NL to get the specs on the full extended length of this shock.
Have not heard back from them yet so, to be 100% sure, I hadn't commented again.

Here are a few points, regardless of whether the car is slightly jacked off the ground.

1) just the weight of the main spring, the shock shaft and components and the small lb/in force of the helper/tender would have caused the shock to extend further than it is now if there was ample travel for this application. As seen in pics of the 944 Intrax RSA from around the web-

2), Unless the sway bar is disconnected from the driver or passenger side, the sway bar alone can support the weight of the wheel from drooping as far as it will see in actual driving conditions, so the relation between the shock eye and the receiver thread on the arm is pretty close to actual regardless of the car being slightly off the ground.

3) Even if the conditions of #2 were met, if the rubber torsion arm bushings are still in place, even this can somewhat cause limited blade movement when the car is jacked.

ninefiveone - You still are not understanding the illustration I made up in emachine, (yes, instead of being appreciative of someone going way out of their way to help you, you slung mud by demeaning the software tool I used [I had to download that at home on my new desktop just to get my point across] to try to explain the difference of your bolt/stud in shear vs the old accepted and proven shock bolt receiver)
I don't hold anybody up as the second coming of Jesus Christ, Karl Poetl included. You used some kind of analogy (or whatever) above that if I was "disagreeing with Karl", I must not know what I'm talking about. When in the long run, I never disagreed with anything that you showed pertaining to the broken bolt and your advice from Karl, you just went off on a tirade that the "fix" he showed you is in all ways better than what I described in the illustration.
When you are airing your problem on a public forum, the reason is, YOU DON'T KNOW and you are hear asking for advice.
Nothing wrong with that.
Go search back from now, in sequence of back history and you will see that the only reason for my participation here is to be helpful to people who DON'T KNOW.
You made an accusation that I demeaned your experience and your driving ability.
Then you failed to demonstrate this when I asked you to quote it (with a "please").
I air just about everything I do in car building, innovative ideas, etc, except for those that I don't care to share (because we compete) with other racers.
Someone like you that claimed "you underestimate me, I have track experience all over the country", should be able to post up some track times or results then for comparison to back up that claim, but you didn't...., so I took you for your word, even in the light of you unnecessarily trying to diminish my experience and/or knowledge.
I can post links of results.....from cars I built with my own hands...TOTALLY, the entire cars from body/paint, roll cages, engines and transmissions.....and suspension too, without the help of Racer's Edge or anybody else. My cars are as fast and well set up as any SP2 944 in the entire country and I have the results to prove it.
This is not a knock on Racer's Edge or Karl himself, who I hold up as a top performance company and one of, if not THE fastest SP3 driver that we have run across in the South East or maybe the whole country.

Too long winded, I wish you all the luck in the world bruh, and the least pain in doing so,

T

ninefiveone

Sorry guys, the helper spring being compressed in the pictures is a red herring. I spun the pre-load all the way down on the driver side to ensure the shocks were fully extended and the passenger side is compressed a fair bit from the car being jacked up on the driver side.

In any case, I've sourced new mounting hardware and have the car standing on it's own again. The math says that a Grade 8 M14 bolt torqued to 150 ft/lbs should have a shear strength of 18,500lbs and enough preload into the joint that all of the load should be passing through the joint rather than the bolt. This is a temporary step until I reinstall torsion bars, but I'm going to be doing some testing all the same.

The engineering on fasteners is fascinating. Bolts in single shear will have about 60% of their ultimate tensile strength (which is a function of pre-load, material, and diameter). More importantly, a well designed single shear joint will pass 80-90% of the load forces through the joint due to friction from the clamping forces, and the rest through the bolt so that you minimize fatigue and fretting damage to the bolt. i.e. the bolt's shear strength should be secondary to the pre-load that you apply to the joint. So an M14 Grade 8 bolt has an ultimate tensile strength of 150,000 lbs/in2 but how much clamping force you actually create is dependent on how much you torque the bolt to. 150 ft/lbs of torque converts to 17612lbs of clamping force. Assuming a friction co-efficeint of .2, that translates to friction force of ~3500lbs. This is why Karl stresses torquing to 140-150 ft/lbs with his or any setup (like Cloud9...68's and mine). You want that single shear joint to have enough clamping force that the friction force carries the bulk of the load. A friction load that's a little more than the weight of the entire car gives a pretty good margin.

The reason the stud failed is because the stud bottomed out in the control arm. 150 ft lbs of torque were not being fully translated into clamping force, too much was being translated into compressive force on the end of the stud where it was bottoming out in the control arm. That allowed movement in the joint, and fretting of the stud which created a stress riser. I'll post pictures of the snapped stud later but you can see where the break started as fretting on the stud.

Most people here felt the mounts were sketchy because they didn't look "beefy" but it turns out the issue is about tension, clamping forces, and lack thereof.

So all this learning about the engineering of fasteners is good and well, but has nothing to do with my experiment on getting dual effective spring rates at the wheel. That experiment is waiting on finding time to reinstall the torsion bars. Stay tuned...

mj951

Nice summary on fastener strength, thanks for sharing.

Droops83

Well, those pics were slightly misleading, but I'm glad that you figured out the issue. Studs are fantastic for maintaining a clamping force in a single plane (such as a cylinder head), but much less so when heavily loaded in single shear . . . .

I hope you can get your coil/torsion spring rate setup figured out as well.