G-E Posted May 20, 2014 Share Posted May 20, 2014 I have a question about that aluminum spacer for the rotors, is it possible the wheel stud heads were sitting just a touch above the surface of where the rotor mounts? Could that aluminum ring have been inadvertently "helping" it fatigue by pushing on the stud areas? It's hard to tell in the pic, but your stud heads all appear shiny, as if they had been rubbing... Quote Link to comment Share on other sites More sharing options...
wheelman Posted May 20, 2014 Author Share Posted May 20, 2014 I won't swear to it but I don't think the rotor spacer ring was touching the studs, if it was there should be marks in the aluminum and there aren't any. I replaced the studs not long ago, that's why they're clean. The more I think about the suggestion that the center of the wheel flexed enough to deform it while was mounted to the hub the less I believe it. I see no way for that metal to flex while it was clamped to the hub unless the mating surfaces were already deformed in some way. I can see how the spokes might flex but think that is highly unlikely unless the wheel slid sideways into a surface at some point, which has never happened I've owned them. Quote Link to comment Share on other sites More sharing options...
Phantom Posted May 20, 2014 Share Posted May 20, 2014 Ken, 6061-T6 is some pretty good stuff - and definitely lighter than steel - but not as strong. Whether they are strong enough I couldn't say. I don't have enough specific experience there. The steel ought to be less expensive though and just a tad heavier than the cast because of the increased density. If you really wanted to go for it you'd use thru-hardened 4340 and you'd never break them. Quote Link to comment Share on other sites More sharing options...
wheelman Posted May 20, 2014 Author Share Posted May 20, 2014 Thanks Bill, I'll have to look into it, we just hired a new ME where I work who has experience designing car parts and running machining equipment. We might be able to use the company's prototyping CNC to fab up a couple hubs. The part I'm not sure of is dealing with the bearing races that would need to be pressed in once the machining was done. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted May 20, 2014 Share Posted May 20, 2014 I love the video! The part where your wheel passed you is the part where I usually climb under the car to get about 5 cones out from under my oil pan. Im gonna stick to my hypothesis till i hear something better or I start to be a bother. When a stock part fails on my car, it is usually the fault of the aftermarket part bolted to it. I think I saw the G-meter hit at least 1.2 several times-you are generating some serious lateral power and are a way better driver than I am. For the sake of future discussion, can you post a picture of the front-side of the wheel mounting surface? If it is flat, it will flex more than the "spoked" part because the spoked part is arched. I think it is flexing between each stud. On production steel wheels, the stamped hubcap mounting circle served a dual purpose of stiffening the wheel center. If the wheel center is flexing, it lets each wheel stud see the full cornering force rather than distributing that force to all of them and all the hub and spindle together as a unit. If the back surface of the wheel is bent, then just mounting the wheel puts bending forces on the hub even when it is sitting in your shop. Fatigue cycles, then pop! I have seen some steel wheels at dirt track and land speed that have a thick steel plate that reinforces the wheel mounting area. In fact, I think it is a requirement at land speed for cars exceeding a certain speed. And theoretically they generate minimal lateral Gs unless in a spin. Listening and learning. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted May 20, 2014 Share Posted May 20, 2014 I just reviewed the pics and the whole discussion. When you have time take one of the broken sections off the wheel and fit it back into the puzzle that was your hub. If the studs hit the spacer, that's your problem. Put a straight edge on the wheel mounting surface to see if it is deformed, if so that's your problem. I wonder, could your new studs have thicker "buttons" on the backside? If neither, I'm scratching my head. The stock 280z hub has no scalloped cut outs so it should be stronger. But, it has different backspacing for the rotor, so switching would cause you to have to get different rotor spacers. I will hush now. Quote Link to comment Share on other sites More sharing options...
G-E Posted May 20, 2014 Share Posted May 20, 2014 Yea don't dismiss wheel flex so easily, if you have ever noticed how many hub caps fly off in intersections, you'd realize steels are made to be cheap.... as a kid I remember piles of hubcaps on the shoulders driving around town And I wasn't suggesting the stud interference on the aluminum ring was a lot, just that having a push on one side, and a pull from the other, especially when the flex will radiate to the opposite side radially, is bad news; I think you subjected it to complex bending forces that just couldn't take 1g for very long... even 240sx's break hubs road racing, even aftermarket hubs I also agree, aluminum is not the way to go, you might start with a "stronger" part by using thicker flanges and bearing section, but aluminum continually loses strength over time, even when it's only mildly loaded --- ask any aircraft mechanic I think 4140 will be resilient enough to use, it is easily hardened/tempered to the characteristics you want, and has a higher deformation strength than even 4130 -- I can provide you with some quality wheel studs to match Quote Link to comment Share on other sites More sharing options...
wheelman Posted May 20, 2014 Author Share Posted May 20, 2014 Ok guys I won't dismiss the wheel flex idea, it just seems that when the wheel is bolted to the hub and it's torqued down (which it was) it creates a stronger assembly which would prevent the center of the wheel from flexing, at least the part that's bolted to the hub. Outside of that center section only the strength of the steel keeps the rest of the wheel rigid. Once I get the car off the trailer I'll take a close look at the center of the wheel and "put the puzzle that was the hub" back together to see if it's possible to tell why it failed. My suspicion at this point is the center of the wheel was bent and putting stress on the hub, why it was bent is the real question. As for the G forces from the video, I'm not sure how accurate they are, we used an iPhone as the measuring device. In prior events we were using an android tablet and saw instantaneous lateral G loads over 1.8, acceleration Gs over .8 and deceleration over 1.0. It's amazing what a good set of sticky tires will do with a well setup suspension. You'll notice there is no aero on the car, it's all mechanical grip. Wheelman (Ken Wheeler) Quote Link to comment Share on other sites More sharing options...
johnc Posted May 20, 2014 Share Posted May 20, 2014 I don't think wheel flex is the issue. From the pictures it appears that the wheel and/or spacer was not flat against the hub face and the mounting ears were put in tension as the lug nut were tightened (as mentioned). Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 20, 2014 Share Posted May 20, 2014 Plain old metal fatigue? Fatigue is its own special world, fairly independent of strength or modulus. Even tiny amounts of flex, of which there's always some, over time can eventually fatigue a part. 41 years is a long time. Quote Link to comment Share on other sites More sharing options...
wheelman Posted June 1, 2014 Author Share Posted June 1, 2014 UPDATE: I finally got the car off the trailer and into the garage, I decided to wait for a set of hubs from Logr and install a replacement so I could drive the car instead of trying to use a floor jack. We had a bit of an issue, the first set of hubs he sent me were actually 280Z versions and I had to use washers to space the rotor correctly. Ok, so the damage is minimal and mostly cosmetic but here is a list: 1. The fender is toast but I'll use part of it to repair rust on a free fender I got. 2. The ball joint will need to be replaced (the bottom of it was ground off when it scraped on the ground). 3. The bottom side of the lower control arm was scraped up, the arm is fine. 4. The bottom right side of the cross member was scraped up, it's also fine. 5. There is a fender support right at the back of the fender well (closest to the door), it was folded back and mangled. I was able to mostly straighten it. 6. The lower radiator support was bent up when the car fell off a jack while putting it on the trailer. The radiator seems to be fine. 7. The center of the rim is bent so it will have to be replaced. The deformity happened when the hub broke, didn't cause the hub to break. 8. Two of the studs were stretched enough by the force during the failure that they were loose, these were located in the wheel where it was bent so were in the last part of the hub to break. Hope that made sense. Things that were not damaged: 1. Spindle and strut are fine 2. Brake rotor was untouched, didn't touch the ground. 3. Main chassis components, they are no more or less straight than they were before the incident. This is a real relief, if the chassis was tweaked more I'd be parting the whole thing out. To answer some of the questions: 1. The aluminum rotor spacer I had installed had nothing to do with the failure, it comes no where close to touching the back of the wheel studs. If anyone doesn't believe me just look at the backside of your own hubs and you'll see what I mean. 2. The center of the wheels I have are not completely flat, they touch the hub at the center opening in the wheel and the outer edge of the hub, so this may have contributed to stressing the hub. I'm not convinced of this though as all the lugs were always torqued to 90 ft/lbs which is really not that much and should have evenly spread the force across the hub face even though the surfaces were not actually touching where the studs pass through the hub and wheel. 3. I tried to put the puzzle that was the hub back together but the parts are too distorted. My conclusion is this hub had developed cracks which I didn't see, then failed when I hit the seam in the pavement with the wheel sliding slightly sideways. The Hoosiers are very sticky and the hub was the original 40 year old one that came on the car when I bought it. Bottom line is it's going to cost me the price of at least 1 new Hoosier A6, a ball joint a new wheel, some sand paper, black and gray primer and the time to put it all back together. I estimate $600.00 to get it back to where it was before the incident. Wheelman (Ken Wheeler) Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted June 2, 2014 Share Posted June 2, 2014 I think I'm gonna be shopping for some new hubs! So freakish that the rotor is fine. Quote Link to comment Share on other sites More sharing options...
wheelman Posted June 2, 2014 Author Share Posted June 2, 2014 The rotor never touched the ground. I have roll center (bump steer) spacers between the control arm and strut that space the end of the control arm down below the edge of the rotor. That's why the ball joint was destroyed. Quote Link to comment Share on other sites More sharing options...
cockerstar Posted June 2, 2014 Share Posted June 2, 2014 Hey Ken, Whatever stock suspension pieces you might need you're welcome to from my stash. I should have multiples of everything. Give me a call/text. Quote Link to comment Share on other sites More sharing options...
tube80z Posted June 10, 2014 Share Posted June 10, 2014 Glad to see no one was hurt. I'm curious what cause the failure other than old age. I crack check mine each year when I'm running. So far I haven't found anything. My car generated 1.6 to 1.8 lateral Gs and I pound the FIA curbs. I don't torque my lugs as much but that's probably more to do with the brand. This probably isn't the problem either but how hot do your hubs get? I wonder if the spacer expansion could have worked against the hub. Like I said I'm totally guessing and this is just throwing another thing out there. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted June 11, 2014 Share Posted June 11, 2014 How technically does one do this "crack checking?" I ask in an effort to learn. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 11, 2014 Share Posted June 11, 2014 Keith: https://www.pegasusautoracing.com/group.asp?GroupID=CRACKTEST Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted June 11, 2014 Share Posted June 11, 2014 Thx Quote Link to comment Share on other sites More sharing options...
wheelman Posted June 15, 2014 Author Share Posted June 15, 2014 Glad to see no one was hurt. I'm curious what cause the failure other than old age. I crack check mine each year when I'm running. So far I haven't found anything. My car generated 1.6 to 1.8 lateral Gs and I pound the FIA curbs. I don't torque my lugs as much but that's probably more to do with the brand. This probably isn't the problem either but how hot do your hubs get? I wonder if the spacer expansion could have worked against the hub. Like I said I'm totally guessing and this is just throwing another thing out there. I've never measured them but they don't get all that hot, the rotors don't show any signs of over heating and my understanding is the majority of the heat the hub sees will come from them. The bearings are new with no signs they were getting hot either, the grease in the hub still looks new. I think the failure was due to old age and the abuse I put the hub(s) through over the years I've autocrossed the car. The location where the majority of our events are held is an old round-e-round track with a mostly dirt/grass infield and some pretty tall asphalt edges. I've spun the car off into the dirt more times than I remember which has undoubtedly taken a toll on the hubs. The event prior to when the failure happened I hit one of those edges sliding sideways but the left side of the car contacted it first, I discounted the idea that the right side may have taken a significant hit as well. Anyway, both front hubs are being replaced and I'm gonna start crack checking them several times a season. If the hub had failed while I was at speed during the run the outcome would have been very different. The thought of that happening almost makes me want to run my 240SX vs. the Z, but it's not as much fun. BTW: I'm running vented rotors on the front and the car has not seen a track day since I've owned it (9 years), I doubt it ever saw one before as it was completely stock when I got it and had been sitting for years rusting away in western WA. It's almost completely back together, assuming I receive the wheels I ordered it'll be ready for the next event. Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted June 16, 2014 Share Posted June 16, 2014 Were those 2 loose studs loose because they stretched when the wheel bent or did they never have the opportunity to clamp the wheel to the hub because the wheel was already bent or not installed evenly? Studs are really hard and I would expect them to break before stretching any appreciable amount beyond yield. If the two parts had clearance between them (even a miniscule amount) after the fasteners were tightened, they will be loose when the 0 arts separate. Quote Link to comment Share on other sites More sharing options...
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