Looks to me as if when cut the threads they left no radius at the step, or just threaded 1/2 turn too far, thus making a stress riser. The fracture appears to start from the exact plane of the step. This was one piece, not a stud threaded into a drilled shaft. In the middle photo the fracture began at 3 oclock. This is poor lathe work, and also maybe over hardening.
I’m not a failure analysis expert, but this looks like it might be a torque failure. But that only means that torque was the means by which it failed. It could still be poorly manufactured which cause it not to hold up to the torque spec or normal torque loads. To verify this that will need to analyze the part for material properties.
In reply to TurnerX19 :
I concur. That is a textbook failure.
I think if anyone is purchasing these that needs inspection before installation. That should be easy to see. It would be great to see the top piece and them photoed together showing the failure point.
On that second photo you can see what I think is the machining mark from the cutting head at three o’clock on the flat surface.
Oh. And I would inspect the other one.
Dr. Hess said:OK, no one ever says "I wish I bought those shocks from that company that doesn't answer the phone and could care less about me staring at their broken crap on my car instead of the Koni's, where I can call up the custom shop and they will answer the phone and fix whatever issue I might have or answer any question."
That's fair enough :)
I wish there was a better way to know who had crap service before hand, because I would have absolutely fallen into the same trap with KW..
I don't recall the exact TQ requirements for the kit, but I do remember initially TQing the top nuts to ~25ft-lbs, which should be well within range.
On my shakedown run immediately following install, I had banging from both rears when going over rough roads. I went back home and removed the rears, and found that the spring caps were not fully seated to the shaft shoulder once the springs were wound-up to their final ride height (nearly max ride height for these units), and on compression the shaft shoulder was banging into the underside of the spring cap. This required that I tighten the top nut again so they are all the way seated with the fully tensioned springs. I can make an illustration if needed. Effectively, the 25ft-lbs was not enough to overcome the force produced by the loaded springs.
That said, once the spring-cap was seated, there was no need to overtighten against the shaft shoulder. I don't see how the shaft itself would've seen too much torque.
Image if helpful to visualize: 
KW's hardware seems to be generally good quality but I've heard so many stories of crap customer service from them, I don't think I'd put their stuff on a car I can't afford to have down for ages. It's bad enough with other coilovers where you have to wait for a replacement strut to ship to you, but KW doesn't even give you that option!
Properly machined and properly heat treated those shafts should withstand 60 ft.lb. or more without complaint.
TurnerX19 said:Properly machined and properly heat treated those shafts should withstand 60 ft.lb. or more without complaint.
That's my thought, too. You'd really have to try to overtighten the spring-cap to the shaft shoulder. Most of the tightening TQ is resisted by the loaded springs if you assemble them in that order (which you should AFAIK).
I've always assembled anything coilover-type (struts included) with the springs still compressed. Top bits go on, nut gets tightened (I'm usually lazy and blast it on with an impact on the lowest setting). Then the spring compressors get released. Otherwise, on a setup with a lot of spring preload that's asking an awful lot of the thread on that nut (as far as tightening it down with the spring pushing against it instead of the threads only having to take that load after it's tightened).
thebigchill said:TurnerX19 said:Properly machined and properly heat treated those shafts should withstand 60 ft.lb. or more without complaint.
That's my thought, too. You'd really have to try to overtighten the spring-cap to the shaft shoulder. Most of the tightening TQ is resisted by the loaded springs if you assemble them in that order (which you should AFAIK).
That's not correct. Assuming that's an M10 thread, torquing just to 25 ft-lbs is generating north of 5000lbs of tensile force at the clamping surface, way more than the spring is generating in resistance. I'm not really trying to defend KW and I'm not saying it couldn't be a material or manufacturing failure, but given the nature of the failure and you admitting you ran them under-torqued for a minute, it's going to be hard to completely rule out installation error as a cause. Now that doesn't excuse their bad service, their response should really have been either "yeah we'll send you a new one" or "sorry, looks like you screwed up the install, that's your problem."
On a different note, konis are pretty great for what they are. But what they are is dirt cheap "performance" shocks. I've seen at least a few be DOA or broken within a few thousand miles and the internal parts are thoroughly underwhelming.
Let's backup a second. When these were first installed on the car and I spun up the perch height to where I needed it (after mounting them to the chassis), the spring-cap was no longer seated on the shaft shoulder, causing the first round of banging. How can this be an issue of over-tightening?
Well after that you tightened them to some further amount, no? And who knows what kind of stresses and fatigue were put into the parts when a connection that was supposed to be clamped down fully wasn't. Like I said, hard to rule out mechanical failure but also hard to rule out user error.
That's true, yes. Now that I think about it, for my initial assembly of the coilovers I tightened the top nut while the springs were spun down, then spun them up, then installed and set ride height. The second time around I tightened them down fully loaded, I think.
Is it possible that a combination of the high ride height and spring loading + compression and seating of the new upper bushings caused the gap to appear between the spring-cap and shaft shoulder on my shakedown run? I'm just trying to visualize how this would happen.
I feel for KW in this case. Simply sending out new high-dollar parts to everyone who manages to break one can get out of control in a hurry, especially when there's no motivation for the customer to send in the broken parts once their car is fixed. Also, when you're done, you have a used shock that you can't sell so you're just throwing parts away - parts that may not have been faulty in the first place. This drives up costs which drives up prices. But customers do get pretty outraged when they don't get exactly what they want immediately. Companies go back and forth between trying to satisfy customers and trying to control return/warranty costs all the time, and the margins in (most) of the vehicle aftermarket are not as high as you might think.
I have concerns about KW's engineering based on their actual fitment - they contacted us about selling their ND shocks, and the decrease in suspension travel was spectacular. Their rear springs are only 200mm (8") long, which means somewhere between 4-5" of actual travel. We have to use 12" rear springs to avoid bind in our coilovers.
I don't think the OP was asking them to send a replacement for free, he was willing to buy one and get reimbursed when they complete a failure analysis. AFAIK, most of the other shock manufacturers do this. While the installation process the OP did is suspect, KW's customer service is Horrible. They're about the last guys making high end coilovers for the Audi B5S4 chassis and hearing this sucks.
That's a decent option, but it's not always a popular one with customers because they have to lay money down. The supplier still ends up with an unsellable shock at the end of it. So it's either the best compromise or the worst.
In reply to Keith Tanner :
Unfortunately when parts fail, sometimes the manufacturer has to take a hit. That seems like a given. My request here and previous experience is that I buy a new unit, then send mine back and potentially receive a refund once assessed. Surely you're still a customer of something, Keith, and while your response here understandably favors the vendor, I don't expect that you would like this approach to customer service if were on the receiving end.
Keith Tanner said:That's a decent option, but it's not always a popular one with customers because they have to lay money down. The supplier still ends up with an unsellable shock at the end of it. So it's either the best compromise or the worst.
I gotta disagree here. Here where I work, if a customer calls in with a failure or premature wear, we ask for some pics and ship new parts either no charge UPS Red on our dime or ask the customer to buy new parts/pay freight and return the old ones for evaluation and a potential credit. The exact course of action really depends on three things - the customer, their rapport, and the type of failure and risk/exposure to us.
As far as used parts not being sellable, thats true but they do have value. Sometimes I want parts back even if I just throw them in the dumpster when they show up because it keeps them out of the hands of the competition - both from a sales tool and an R&D perspective. Last thing I want is my competitor to show up to a customer and use our failed parts as a sales opportunity. Sometimes we will build up as-is/no warranty assemblies out of returned used parts that still have life for some of our cheaper or homeboy hookup customers who understand that they can get lightly used stuff for half price.
I guess where I am going is in the grand scheme of things, it doesn't cost us a whole lot to take the "customer is always right" philosophy. One thing it has done is soiled me to how poorly most companies treat customer service and concerns. Seem most of them are in it for the quick buck and do not care much about the after sales support.
Admittedly, there is a pretty big difference between sending a customer a few $300 service kits on the arm for a million dollar piece of equipment and giving every flatbrimmed fucccboi with a stanced out Miata free parts at the drop of a hat.
Sorry to hear about the experience so far.
This is why I ran factory parts on my commuting cars before I lived within biking/walking distance of my office. Keeping a car operational with boring, reliable parts is expensive enough as it is.
Dr. Hess said:OK, no one ever says "I wish I bought those shocks from that company that doesn't answer the phone and could care less about me staring at their broken crap on my car instead of the Koni's, where I can call up the custom shop and they will answer the phone and fix whatever issue I might have or answer any question."
Just because it is not inexpensive doesn't mean it is not cheap crap.
People buy on price in both directions. "If it's expensive, it has to be good!"
thebigchill said:In reply to Keith Tanner :
Unfortunately when parts fail, sometimes the manufacturer has to take a hit. That seems like a given. My request here and previous experience is that I buy a new unit, then send mine back and potentially receive a refund once assessed. Surely you're still a customer of something, Keith, and while your response here understandably favors the vendor, I don't expect that you would like this approach to customer service if were on the receiving end.
No, I said I felt for them. The customer side of this story has been well expressed, and it's a familiar tune. But it's not as easy as you might think, I was just showing what it looks like on the other side. Having been on both ends of this, I'd like to think I've got a slightly different understanding of the realities for both parties.
Customers that are willing to pay for a new unit are not universal. That's a policy that will also create some friction - as I said, it can be the worst of all options if all it does is piss off the customer and the vendor still ends up with unusable parts at the end. If you're going to do that, you might as well not piss off the customer in the first place. Or, if you're accepting that you'll piss off the customer, you double down and make sure it's at the lowest cost possible. I'm not recommending any or all of these, I'm simply trying to lay out the thought process.
93gsxturbosaid:I guess where I am going is in the grand scheme of things, it doesn't cost us a whole lot to take the "customer is always right" philosophy. One thing it has done is soiled me to how poorly most companies treat customer service and concerns. Seem most of them are in it for the quick buck and do not care much about the after sales support.
Admittedly, there is a pretty big difference between sending a customer a few $300 service kits on the arm for a million dollar piece of equipment and giving every flatbrimmed fucccboiw ith a stanced out Miata free parts at the drop of a hat.
A very big difference!
I've seen a number of companies go through this - they move back and forth between trying to do everything for the customer and trying to protect themselves from the customer. Once you get into the latter mindset, you have a real problem. We've been through it several times in the past couple of decades, I'll admit, and it can be hard to convince the beancounters that throwing money away is the best choice. And the relative cost/value of the product is always a factor. If you've got a huge margin or it'll only take a couple of bucks to fix a problem with an expensive part, that's an easy call.
Selling used/seconds is expensive enough that it's often not worth it. Unless you have large volumes of the stuff, you have to spend a lot of time documenting and tracking and fulfilling the order, far more money than you'd spend on a normal, new product. It hurts to take something like a perfectly good coilover that just needs a rebuild and chuck it in the dumpster, but in reality it may be the most cost-effective solution. I have a collection of coilovers sitting around my desk that attest to this, ones I can't bear to toss but should. The other option is to do what so many Amazon sellers do, just put the returned part back on the shelf as new. We all know how that turns out.
z31maniac said:4k miles and the shock bodies have that much corrosion?
Koni Yellows corrode even worse after less time. I swear they start to rust the day you put them on.
I found a similar instance of this happening, but to a Bilstein HD on a Porsche. Note how the shaft broke on the topside of the assembly. This to me would suggest over-tightening more than my scenario.
https://rennlist.com/forums/993-forum/594499-broken-piston-shaft-on-a-bilstein-hd-front-strut.html
Same here: https://www.lxforums.com/board/tires-wheels-and-suspension/359289-broken-eibach-strut.html
And one like mine: https://themustangsource.com/forums/f726/steeda-upper-strut-mount-snapped-537291/
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