Current FFR Bilstein Shock Issue!

[mrmustang]

Originally Posted by Hoofa

For the people that like a little vodka in their Koolaid, What do we think about my nuts? I'm not an engineer, but I can make or break anything.. I believe in them enough to send them out for free... In the hopes that St. Peter will overlook some of the other stuff...

Hoofa,

Attached is what was originally posted by me in regards to a Bilstein shock failure, clearly the pictures are no longer on my server that accompanied this post, but the facts and the third party (without a financial hook in this battle) analysis (from a shop that rebuilds Bilstein shocks for race teams all over the country) show what the real issues were. After reading this analysis, you might want to reconsider sending out the nuts.

Bill S.


Originally posted 03-25-2006, 09:34 AM on FFcobra (and still located on their server, maybe this one as well):


"Ok, let's start off with the Bilstein shocks as submitted by Marty D. who wrote to me the following:

"the shocks were mounted with body up on the front suspension. Lower control arms are from Fortes. I had some spacers between the spring hat and the heim joint to prevent any interferance from occuring with the lower arm. When I looked at the shocks I couldn't see any signs of contact between the arm and shock. There are about 5k miles on the shocks. Many of those miles were on bumpy back roads driven at speed."

Ok with that out of the way, let's look at cause and effect with the following four photo's:






From the looks of things, there was not only some unusual lateral loads (wear on the outside of the lower spring seat and threading), but my shock guy (a custom rebuilder and master WD for Bilstein, QA1, Carrerra, and Pro Shock) sent me the following email:

"From the shock it looks like the center to center of the mount on that car are at 14.5 " center to center this will allow a 5" stroke on the shock and looking at the shock, also looked like there was only 2" of shock left when the car is at ride height so that means there is only 2" of shock available to extend so constant battering on that shaft at full extension is what caused that shaft to rip off. By no means was that a shock manufacturers fault but a poor choice of mounting a street car should have at least 7" of shaft length to deal with at ride height 3/1-2 " of shaft for bump and rebound the reason that some other shocks might get away with the constant beating full extension is that the QA1 shocks pro's and carrera shocks use a thicker shaft that is much softer than the bilstein but this still does not make it right".


Just thought you would like to know his thoughts on first glance, he is going to take them completely apart in the next day or so to check the valving to see if anything failed there as well. If he finds anything else of interest, I'll let you know."

[mrmustang]

Original post here:
Third party shock failure analysis with pics

Original post on ffcobra:
http://www.ffcobra.com/forums/showthread.php?t=154461


Again both posted the same day back in 2006 .



Here we are in 2008 with the same issues, so the question remains, what is the difference between then, and now?


Bill S.

[Hoofa]

That is the only concern with my nuts. That they steal a little travel. The next batch I'm making are going to be significantly shorter. After I broke them I figured out that I don't need the sleeve to be nearly as long. Basically it comes down to the lesser of two evils. If the shaft is going to be taking a beating anyway, I'd rather the beating is on an area that has 40% more material and isn't scored. My new nut without the magic washer should only steal about 3/16" of travel. Can you ask your Shock guy about the nuts? I can't afford new shocks, I blew my wad on my nuts....

[lineslinger]

Originally Posted by BobTheBuilder

"Bucko...neener neener"

How cute. Just like a five year old.

"If you wish to know the mind of a man, listen to his words".

Having read this from beginning to end I'm going to chime in.

There are posts from those that offer reasoning and contribute solid information to offering me a better understanding of the issue......

Then there are offerings such as the participant quoted above, who, upon reviewing this posters contributions and those of a couple of others, it has become clear that these participants.........

[mrmustang]

Originally Posted by Hoofa

That is the only concern with my nuts. That they steal a little travel. The next batch I'm making are going to be significantly shorter. After I broke them I figured out that I don't need the sleeve to be nearly as long. Basically it comes down to the lesser of two evils. If the shaft is going to be taking a beating anyway, I'd rather the beating is on an area that has 40% more material and isn't scored. My new nut without the magic washer should only steal about 3/16" of travel. Can you ask your Shock guy about the nuts? I can't afford new shocks, I blew my wad on my nuts....

Hoffa,

Look at this line again:

also looked like there was only 2" of shock left when the car is at ride height so that means there is only 2" of shock available to extend so constant battering on that shaft at full extension is what caused that shaft to rip off.

Again it's an over extension of the shock shaft itself that is most of the problem as the shaft vs travel is not long enough and it over extends causing the failure. Not the opposite of maximum contraction of the shock shaft. Still unsure what effect your shock shaft nuts would do in this situation, not sure I would want to test it out either.

As for asking the Master WD rebuilder about your solution, he is now 130 miles away and I cannot just stop in and ask him. I will send him a copy of your pictures and will post his response here if I get one.....



Bill S.

[lineslinger]

Originally Posted by Hoofa

For the people that like a little vodka in their Koolaid, What do we think about my nuts? I'm not an engineer, but I can make or break anything.. I believe in them enough to send them out for free... In the hopes that St. Peter will overlook some of the other stuff...

Just so I understand correctly, by beefing up the stress/break point on the rod by encasing it in a longer heavy walled nut is that intended to strengthen the break/stress point?

If indeed this is the intention would not that stress be passed on to the next weakest point in the "link" and cause potential fracturing or over-stress that point as well?

[Hoofa]

If you study the breaks, you can clearly see that it is caused by many small side loads. There will be side loading throughout the range of the shock. The nut transfers those loads to a much more robust area of the shaft. With no scores in it. I'm going to go break something, I'll be back...

[mrmustang]

Hoofa,

It is not sideload that is breaking these shafts. Having bent enough old Bilstein shafts to prove that point back in 2006...........


Bill S.

[Hoofa]

The shafts don't bend they snap, they're very hard. The ares where they break, bends, as it's softer metal with a sharp cut into it. Repeated cycling is the enemy. Again I'm not an engineer, just a guy that couldn't afford new shocks to replace my new shocks. This is great being able to discuss this issue. This is how we'll fix this problem, with open discussion. This is after all why Al Gore invented the internet.

[Hoofa]

This is a text book break.... I just looked it up in a text book. That area is a textbook example of a fatigue break. Two beach areas, final break perpendicular to max stress. Huge stress riser. Fine grain steel is particularly susceptible to stress risers. I would guess that the tensile strength of the shaft is greater than whatever is holding the shaft in the shock body. I'm not doubting that the shock is too short, I just don't think that is the root cause of the breakage. Were the Proshock failures from being pulled apart?

[Hoofa]

Originally Posted by TButtrick

From my recent education in fracture analysis, It looks as though FFR built in a good margin of safety. Notice how large the beach areas are compared to the area of final fracture. If you could just take that stress riser out of the equation, it would probably be a pretty strong shock. How could we do that??? Big nuts??? Prove me wrong, I've been an expert in this field for about 15 minutes.

[mrmustang]

Hoofa,

Your still thinking this is a lateral load or overload issue when it's not. Again most of the breakage is not of a lateral load issue. Some are due to misalignment, or incorrect installation, but not the majority of them as you have been lead to believe. Once more, FFR (both Jesper and Dave Smith) had this unbiased third party information along with pictures and in one case the broken shock(S) that was(were) analysised back in 2006.........


Bill S.

[mr bruce]

http://en.wikipedia.org/wiki/Hydrogen_embrittlement

[TButtrick]

Hoofa,

Trying to understand how that nut is installed. The shaft doesn't seem to have the thread length to accept a long nut plus the rod end.

I've always felt the rod ends are being installed incorrectly by a few but not certain it could be attributed to any type of fault. I watched a fellow builder take the lock nut and ram it down on the shaft as far as it would go then take the rod end and tighten it against the lock nut. I'v been told never to bottom the lock nut like that but rather turn it CCW toward the rod end with a wrench on the rod end to snug them together.

[mrmustang]

Originally Posted by TButtrick

I've been told never to bottom the lock nut like that but rather turn it CCW toward the rod end with a wrench on the rod end to snug them together.

Who ever told you this is 100% correct, you never ever want to bottom out the rod end and the lock nut at the very bottom of the threaded shaft.



Bill S.

[Hoofa]

Originally Posted by mr bruce

http://en.wikipedia.org/wiki/Hydrogen_embrittlement

If we could just channel the hydrogen away from the shock and into the engine we'd be in business! That's a win,win.

[Hoofa]

Originally Posted by TButtrick

Hoofa,

Trying to understand how that nut is installed. The shaft doesn't seem to have the thread length to accept a long nut plus the rod end.

The nut has a interference fit sleeve that slides over the thicker part of the shaft. It has the same amount of threads as the original Jam nut. It just isolates that super ****ty area of the shaft so the only forces it sees are tension and compression. It transfers the bending forces to an area of the shock that has a 42% greater cross sectional area and better metal. That area of the shock is built like a samurai sword. It has a tougher core with a hardened shell. And NO stress risers. Fine grain steel is very sensitive to stress risers.
I'm thinking about breaking a couple more shocks today to see how short I can make the sleeve.
Someone tell me I'm wrong so I don't waste any more time or money.

[mrmustang]

Hoofa,

I love your work and your ingenuity, but the real issue at hand is not on the compression stroke but on the extension as the shock can only extend an addition 2" before maximum travel has been achieved, thus causing the stress fractures because the shaft cannot extend further than it's maximum length vs the additional 1-1.5" of suspension travel on uneven roads or potholes allows in real world driving. Think of pull instead of push on the shaft and you'll understand where I am coming from.



Bill S.

[Hoofa]

I completely understand what your saying. But the way the shaft fractures, tells me a different story.

[mrmustang]

Originally Posted by Hoofa

I completely understand what your saying. But the way the shaft fractures, tells me a different story.

Go back and study all of the pictures again, as the last several show two different fracture signs, one from the over extension, the other from a side load. Do you not see the difference in the two different shocks?


Bill S.