Gentlemen no reason to get personel, this a a chance to learn something.
Mike;
Show us the calculations. Exactly how does the 1" norrower track cause this. The severe tuck under was caused by the axle slipping outward and causing a lot of positive camber. I didn't see what exact tire size or wheel size he was running but many of us in this perfromance blog run widder wheels and tires.

Noonie;
I have a stock axle and work for a company that ownes 8 heat treating plants and have lots of testing equipment, I will check the hardness of it and look to see if I have a clip. will report the results later this week.
Jim

 

No one I think is in your tree.
I mean it must be high alone.

-W

 

The calculations are gone, as is the ability to re-do them as stated many times before. There's nothing stopping any enterprising soul from re-doing them, in fact two other members have independently done them, and come to the same conclusions that I have. I stopped at 1G lateral load, the other two gentlemen went beyond that to (IIRC) 1.3G or more.

Understanding the positive load inwards is simple. Refer to the drawing above. The critical pivot point for the yoke to be able to slide in/out of the diff is at the outer end of the lower strut rod (also mounting point for the lower end of the shock). A rigid joint here would make movement impossible not just for the yoke, but for any vertical movement of the suspension.

To create an inward load on the yoke, the spindle ***'y is designed with the centre of the tire contact patch offset outboard of the pivot point. The greater the offset, the greater the leverage pushing the yokes inwards. If the pivot point were directly in a vertical line with the centre of the contact patch, the wheel would indeed flop in and out as many believe. But it isn't- static inwards load, as stated many times before, is 300 pounds given the typical weight on a C3 rear wheel.

More difficult to calculate and visualize is the addition of a lateral force acting on a tire and the varying vertical load of the car leaning in corners. As a surprise to me (and the ongoing disbelief to some here) the load of the car 'leaning on the tire' while in a corner increases at a greater rate than the lateral load of the tire acting as an additional lever trying to pull the yoke out. The net effect is increasing inwards load on the yoke, not decreased.

Critical to the first and second calculation is the amount of tire offset. More offset, more inward load. Less offset= less leverage= less inward load.

Critical to the second calculation only is the radius of the tire/wheel assy. A larger radius will have more leverage than a smaller assy ie, easier to the pull the yoke out.

My calculations were based on stock wheel offset and stock tire diameter. I allowed 1" for contact patch shift.

The famous video shows a car with three things that undermine the designed in 'leverage' that keeps the yokes loaded inwards.

1) less than stock wheel offset
2) greater than stock tire roll under
3) greater than stock tire diameter.

If you look at the video again, you'll see that the tire rolls under long before the yoke pulls out. IAW, it's the roll under that pulls the yoke out, not the yoke pulling out that causes the roll under.

Also of interest is no evidence of the yokes being 'brutally slammed' inwards as maintained by those who believe that this is the cause of cracked diff. spiders or mushroomed yoke ends.

 

I have seen egged out pin holes and cracked posi cases at the pin hole. I have also seen failed C clips on yokes with plenty of spline after the c clip groove all on stock setups without offset trailing arms. All three of these failures logically can have the same cause. The stub axle unloading off the pin and slaming into the spyder and back into the pin repeatedly on hard cornering as shown in the video. The car in the video obviously has worn yokes and a lost or damaged c clip but even before it gets to this point there is some play between the yoke and pin if the inward pressure is unloaded. This play increases as the clutches and or yoke end wear and the impact at the c clip/ spyder gear interface in hard cornering increases. So does the impact on the pin when it returns to the normal position. If there were never any outward pressure pulling on the axle in any circumstance there would be no failed clips unless the side yoke wear is to the clip groove. There would also be very few cases where the posi case had egged out holes or cracking at the pin hole.
Sometimes logic and common sense trumphs over a flawed calculation that may not accout for multiple varying parameters. If the calcs were figured on a sweaping curve and no dips or bumps the parameters of the calculations change when you turn hard one way then the other and or encounter bumps and dips in the pavement or both. A sway bar changes the parameters, a full tank of gas changes them, two passengers or a heavy or light driver changes them, engine and trans weight changes them, front/rear weight distribution changes them. Going uphill or downhill changes them, the type of road surface and tire grip on that surface changes them. Even the power of the engine and a manual or automatic trans will make a difference as will accelerating out of a corner transfering more load to the rear. unless all these variations are figured into a calculation the calculation is flawed and can show drastically different results than the car actually sees on the road under these varying parameters. And, yes a 1" inward offset on the tire contact point is another parameter that will affect the calculation.

 

Hey Mike...
As for as everyone else I sincerly apologize. And as for as me not contributing technical info I did on the last thread and it read a lot like what everyone else is reading here.

 

Your conclusions about impacts are valid.
commonly referred to as "spike loads". The existy in electical, mechanical and fluid systems.
Those loads can be very difficult to account for in intitial design, ending up being many times more than originally calculated, without real world testing.
We designed some hydraulic cylinders with 1 1/2" hardened rod that kept intermittantly failing, but thru field evaluation found we needed 2" hardened rods (in a 3" cylinder no less). That's a major upgrade. Repeated spike loads.

On the hydraulic side, on a normal open system running 2000psi, kept blowing hoses rated at 4000psi working pressure. Only specialized lab gauges could record repeated spike pressures of over 14,000psi. Very short, in milleseconds but damaging nonetheless.

A lot more to it than meets the eye. Some good CAE program load calcs are needed, not just a cad drawing.

 

Sounds good.
Do you plan on cutting the axle so you can get the depth harness too thru the xsection?

I just got my 17000psi failure rating from advertized specs, the big ring manufacturers publish them and I used a pretty base snap ring and the axle I got from someone that sells them and if I remember correctly, they said it was RHC 55, which seems almost too hard.
Anyway, I thought the 17000 for the snap ring application was more than enough considering the supposed calcs were 300.

 

And you can add in flex in the swing arm both vertical twist and horizontal left right thrust.... made better by poly bushings but still there are even twist in the swing arm itself. And your math does not take all the above into account.

Mike, as much as you are "I am truly baffled as to why you or any of the others here cannot understand this."
We seem to feel the same about your thought process here, even after the video, and several, including myself, that have attested to this problem and what it fixed. It seems to me that maybe at one point in time you were some sort of engineer in suspension??? Just guessing here on my part, if so you must agree that there are all these complex variables, and note that the math equation used was not near complex enough to simulate all the different stress and loads. But once again after seeing the video and hearing testimony you still hold fast to this belief?
And on a side note, you were once again the first to start slinging insults...

 

OK, lets' look at this from the opposite end of the horse. This discussion has enough intrigue and mystery to fuel a full season of a TV drama. let's say we want to prove to GM that their design is faulty so that we can sue their a** off and become millionaires. It's Ralph Nader reborn, and this time it's Corvette and not Corvair.

We use the youtube video to demonstrate how unsafe the design is. We show the judge the one minute run with 'proof' that the yokes slide out. In that one minute the yokes slide out for maybe 2-3 seconds total, meaning that they were loaded inwards for 57 seconds. We disclose the test conditions that were required to create the critical 2-3 second pull out. The judge asks: Is this representative of a stock configuration? No. Did the modifications made significantly increase the tendency for the yokes to pull out? Yes. Would the yoke have pulled out in the same manner on a car with NO modifications? We have no evidence your honour. Ooops.

Defence lawyer pulls out calculations done not by themselves but by several independent witnesses that consistently show that as a lateral load increases in cornering, which would pull the yoke out, the vertical load from the car, driver, passenger, gas, sway bar, you name it increases at a faster rate than the lateral load. This resulting net load increases the inward force, not decreases. In other wards, the faster and harder the corner the greater the load. No condition or combination of varying the load of the car and lateral load could be simulated to actually unload the yoke up to 1.3G.

His honour asks if we have any calculations to show that the above studies are invalid. Nope. Ooops.

We move to point number 2- cracked cases and mushroomed yokes, using the 'hammering' theory.

Judge asks to see the film again and reminds us of the extreme conditions required to achieve the supposed 'hammer'. Defence lawyer speaks up, not denying the existence of the 3 seconds of pullout or the existence of mushroomed yokes and cracked cases but pulls out a paper analyzing the strength of the c-clips, even quoting a study undertaken by an enterprising young summer student. This paper indicates that they can withstand a load of 17,000 pounds. This position is back up by another contributor who confirms that they are good for 10-20,000 pounds depending on hardness.

Judge then states that he is not an engineer and has trouble understanding how sufficient pull-out force can be generated to actually snap a c-clip, given the stated strength of the clip and the modifications required to actually unload the yokes. He goes on to ask why, if the pull out force is so great, does the yoke not pull itself all the way out during extreme cornering or even unexpected 'shock loads'. Well your honour, the box-section trailing made of stamped sheet metal stops it, not to mention the flexible rubber bushing we all hate (laughter in the court room as the judge rolls his eyes). So, in summary, a c-clip capable of holding 17,000 pounds is not as strong as the trailing arm and a rubber bushing. OK. Ooops, three strikes.

Ah-ha! We yell, shock loads- that's it! That's what causes the clips to fail and precipitates the descent to the pits of h*ll.

GM lawyer then produces drawings indicating the production clearance at the end of the yoke and hundreds of photos showing mushroomed yokes but intact clips. Judge asks how a shock load is created, given the extreme conditions required to lift the yoke off the pin and the minimal clearance available to create a hammer effect even with mushroomed yokes. Let's see that film again, but let's look at the other side of the car (the right hand rear wheel) . I see no hammering forces that would snap a c-clip he says, even with the modifications made to the car that would encourage such an effect. OOops, another point lost.

We then produce pictures of yokes with missing clips but embarrassingly, not all of them have mushroomed ends. How does this help your case, his honour asks. This would infer that in spite of having missing clips, there is not enough supposed 'hammering' to consistently do any real damage. Is it possible that the mushrooming is caused by another force- maybe by constant high inward loading that wears eventually through the case hardening? How come it's seen on dead stock cars that have NEVER been autocrossed or even driven in a spirited manner? How come there's a steady parade of posters on CF,CAC, DG, NCRS etc that have been knowingly or unknowingly driving their cars with NO clips for years yet have not experienced any handling difficulties?

Uhh, I guess we'll head back to the drawing board.

I'm sure there will be a second episode.

 

First of all, I want to say that was a very clever and nicely written pice.

Lets use YOUR case here, Mike…..


if you insist

 

Calculations? I am starting to believe that it is just all a myth..just how complex of a calculation would it be for ALL the variables to be calculated in? ???

could it be so????

 

Paul-

If you've looked at the drawing above and can't understand why less wheel offset than stock reduces the leverage that pushes the yoke inwards, I'm stumped coming up with a simpler way of explaining it.
Think of a see saw with different length sides. The skinny kid on the really long side has the advantage over the fat kid on the short side. Reduced wheel offset shortens the skinny kid's side.

That's the best I've got. Seriously.


"4. As we have all seen and heard, these “C” clips do fail or somehow remove. ANYONE that has ever swung a hammer or used a jackhammer of sorts knows the head will and does mushroom over time… not at 1, 3-second interval, but over several years’ worth of this would do this mushrooming damage. And any mettle with time and impact will fail, IE ring and pinions, gone through a few of them myself, and they are slightly stronger than the C clip… oops mike… is that strike 3??"


There's no clearance to swing a hammer of any sort. No clearance, no swing. No swing, no impact.

 

do you know what the factory spec for clearance is here for the yoke? but yes, it seems to be that I remember that yoke being very tight.
But if the C clips for whatever reason do come off, then we do have the hammer slap.

Mike, thank you for a civil rebuttal, your court write up was very nice, very cool

And I do believe under normal operating conditions it is all as you state, but I, and I think the others here are all talking extreme conditions, like in the video...

 

"I agree with you on this statement, I believe you are correct. I just also believe that non-offset trailing arms will also pull out... it happened to me and it is not a good feeling."

Paul,

Please, I'm exhausted. It's got nothing to do with offset trailing arms. Nothing.

 

sorry... i was under the impression that the offset trailing arms were used to get the wheel offset you are referring to here... did i misinterpret your meaning here?

regardless... same outcome

I think this is one of those things that readers will have to make there own opinion on, with the facts presented..


and I guess we will have to continue to disagree on this issue until more compelling evidence than the video is presented.... And I think that is going to be very very difficult...


Bet some day here, some new evidence will pop up, and there will be a round 3.... round 1 tie, round 2 "C" clip guys, so until then

 

round 3 is here..... new evidence from the holy grail itself... GM...

This was taken from a post from David_at_triumph a forum member commenting on the same thing on a different thread...

seems the "C" clip guys win once again...

Quoit from David:
I also would like to set the record straight on the great snap ring debate. From the 1963 corvette SAE paper explaining the new IRS, there is a cutaway of the differential and the caption reads:

"Suspension thrust in one direction is taken by snap rings located on the splined end of the short integral yoke drive shafts. Thrust in the opposite direction is through the yoke unit to the differential pinion shaft".

Pretty clearly, the engineers were expecting thrust in both directions. And yes, they did intend the snap rings to both hold the load and act as a bearing. Incredulous as it seems, every design engineer is tempted by the forbidden fruit of the snap ring - I am one and I see it all the time. If you have a car like mine with worn side yokes and an otherwise race prepped chassis, you can certainly feel it. I have a long weekend ahead of me (sic). And I did not intend this email to "pile-on" anyone. Often times designers are worked into a spatial corner, probably with a bad initial assumption that a static analysis would indicate, too late to change the surrounding pieces, and viola, what was once an oversight is cured with a skinny groove and the magic of a snap ring, a feature by golly.
The cross-section with the differential and the quote is on this page:

http://www.web-cars.com/corvette/196...er.php?page=10

A conspiracy assumes I actually know someone. I don't. My only motivation is trying to figure out what is happening with my car and eventually how to permanently solve it.

The loading diagram that Mike is after is on page 5 - it only shows the outboard wheel in a turn in a static condition. I think by watching the video it is pretty clear that the loading is anything but static. If you watch carefully, as soon as the tire rolls from its inside edge (where the static load analysis is applied) to a condition where the load transfers to the outer edge due to hard cornering (or when the suspension is in rebound and the tire is camber outward), this pulls the top of the tire outboard and this is when the snap rings limit the motion.

static load diagram:
http://www.web-cars.com/corvette/196...per.php?page=5

camber diagram for rear wheels, anything over 1" of rebound movement results in the rear wheels being camber out.
http://www.web-cars.com/corvette/196...er.php?page=10


Way to go David!
http://forums.corvetteforum.com/c3-t...utoxing-3.html