Phantom Posted September 21, 2014 Share Posted September 21, 2014 I threatened Wheelman yesterday to rejuvenate this thread when the right front hub on his SBC powered 240Z failed yet agin. Fortunately the wheel stayed on this time - only two of the lug bolt ears broke. Kiddingly I told him to quit hitting curbs and he wouldn't have that problem - oops, there weren't any curbs for him to hit so that let's that theory out. He had just replaced the failed hub from the previous thread and the car was in it's second weekend of racing. It ran in two class with two drivers. Both won their classes and the car set the record time for the day beating out many more "impressive" (read expensive) cars. At the end of the first day the right front didn't seem right to Ken so he pulled the wheel and realized that he only needed to remove two lug nuts to separate it from the car. identical failure as before - two of the hub ears had broken through. OK Guru's - it's time to solve this problem. This car is the one to beat at this track and it's always fun when a 40 year old 240Z beats a track prepared Z06, Lotus, etc. Quote Link to comment Share on other sites More sharing options...
NewZed Posted September 21, 2014 Share Posted September 21, 2014 Same wheels? I got the impression it was a fatigue problem from flexing, because there was a gap at the wheel mounting surface. My interpretation, I couldn't really be sure what was being proposed in the other thread. Quote Link to comment Share on other sites More sharing options...
cockerstar Posted September 21, 2014 Share Posted September 21, 2014 Ken, you're welcome to try out some spare wheels I've got that should clear your brakes just fine. They're narrower than what you're used to though. 16x7 with 225 width Kuhmo Ecstas. I'm sure there's also a wheel hub for you in my stash too. Quote Link to comment Share on other sites More sharing options...
wheelman Posted September 22, 2014 Share Posted September 22, 2014 (edited) I don't have an entertaining video this time as the failure didn't happen on track, but the right front wheel hub broke again. The last time this happened was back in May of this year and the wheel hub totally failed at the end of an autocross run allowing the wheel/tire to exit through the fender destroying it. This time I discovered the failure before the hub completely failed but the same one broke. 2 of the "ears" failed on opposing sides of the hub, broke off completely just like on the hub that failed before. I discovered it at the end of the day when I removed the wheel. Both front hubs were replaced in June with a set I got from Jon Mortenson. They were in great shape with no evidence of being abused or cracked. There were no off track excursions with these hubs but the one that broke only lasted 3 autocross events and maybe a 1/4 mile of street driving. I'll post some pictures tonight. Here are specifics of the car for those of you who didn't read the other thread from May. 1973 240Z 1995 LT1, approx. 400hp at the crank GM T5 transmission Clutch type limited slip R200, 3.54:1 gears Custom CV joint axles Techno Toy suspension arms front and rear (fully adjustable) Ground Control coil overs (springs are 350lbs front and 325lbs rear) Biscuit style camber plates Koni yellow single adjustable struts MSA sway bars front and rear Toyota calipers and slotted rotors on the front, Maxima calipers and solid rotors on the rear Diamond racing wheels, 16x10 on all 4 corners Hoosier A6s, 275/45-16 on all 4 corners Total car weight: 2540 lbs with a 52/48 distribution Suspension setup: Front: -2.5* camber, 4* caster, slight toe out Rear: -2* camber, slight toe in My co-driver set FTD in the car that day and I won my class, it was handling great and was VERY fast, we out ran a Corvette ZR1 with it to take top raw time. One thing I find really strange is in both instances we were able to run 3 autocross events with the Hossier A6s before the wheel hub broke. 2 of us were driving the car so that's about 48 runs (we get 8 runs each per event) between failures. BTW: Bill Davis (Phantom) attended the event and witnessed the broken hub. Wheelman Edited September 22, 2014 by wheelman Quote Link to comment Share on other sites More sharing options...
Phantom Posted September 22, 2014 Author Share Posted September 22, 2014 (edited) Ken, Did you get my PM about the cryogenically hardened hubs? Another thing - I didn't realize you were running 3.54 gears in the rear. With a 6500-7000 redline do you think you might get just a bit more with 3.70 gears? Edited September 22, 2014 by Phantom Quote Link to comment Share on other sites More sharing options...
wheelman Posted September 22, 2014 Share Posted September 22, 2014 (edited) I guess I should've looked closer before starting my own thread on this topic, anyway here's a link to the thread I started: http://forums.hybridz.org/topic/119688-wheel-hub-broke-again/ To answer the questions asked so far: 1. NewZed, No, not the same wheels but the same type of wheels. After the last incident I purchased 2 new Diamond racing wheels 16X10" with 4.5" backspacing. Same basic wheel as the ones I was running before with the exception that the old ones were 9.5" wide. Same tires, Hoosier A6s 275/45-16. We never did settle on a favorite theory in the other thread but I completely disagree with the idea this is due to wheel fatigue or flex, I ran that first set of wheels for almost 7 years before the first failure, this latest hub lasted ~48 runs. 2. CockerStar, thanks for the offer, I may take you up on one of the hubs but not really interested in the rims or the Kumhos. Once you run Hoosiers you'll never go back. I'm not sure what I'm going to do now, the racing season is over and I had already planned to take next year off so I have some time. I have a set of 280Z hubs that "look" stronger but would require modifying my brake rotor spacers, I'm also going to look into going 5 lug or possibly just using the car as a street driver. These "failures" are always going to be in the back of my mind now, especially considering I've dodged the bullet twice with these things. Hmmm, maybe it's time to buy a lottery ticket and retire to some Caribbean island. Edit: I want to correct Phantom, the car we out ran to take FTD wasn't a track prepped Z06, it was a stock Corvette C6 ZR1. Still an impressive achievement considering it was running Hoosiers, makes 700HP and has brake rotors that are as big as my rims (well maybe not but almost) and are made of carbon fiber. It was definitely a good day and this was the 3rd time we'd out run that very car, the other times it was running track slicks which weren't getting hot enough so was traction limited. Edited September 22, 2014 by wheelman Quote Link to comment Share on other sites More sharing options...
Phantom Posted September 22, 2014 Author Share Posted September 22, 2014 Hey Ken - I stand corrected - but - by definition a ZR1 with Hoosiers is a race prepped car. Think what everyone else would have to do to have their car equivalently equipped. With two threads on this now you'll be kept busy answering the questions on both of them. Let confusion reign! :-) Quote Link to comment Share on other sites More sharing options...
wheelman Posted September 22, 2014 Share Posted September 22, 2014 (edited) Bill, Yes, I got the PM and it's an interesting idea, I wonder if there's any place to get them now that MM is defunct. The 3.54 gears are almost perfect for the car, I have the rev limiter set at 6000 rpm which is ~68 mph in 2nd with the tires and transmission. If I went with 3.70s I get a little better acceleration but would drop the top speed at the limiter unless I bumped it up to the range you mentioned. Those rpms are way beyond the cam I'm currently running, the power tops out at ~5800 rpm. I'd rather not push the rpms up, the current setup is conservative but provides plenty of torque and HP to make for a very exciting ride. It's too bad we couldn't get you in the car for a ride, I'm sure you would've enjoyed it. Edited September 22, 2014 by wheelman Quote Link to comment Share on other sites More sharing options...
wheelman Posted September 22, 2014 Share Posted September 22, 2014 Hey Ken - I stand corrected - but - by definition a ZR1 with Hoosiers is a race prepped car. Think what everyone else would have to do to have their car equivalently equipped. With two threads on this now you'll be kept busy answering the questions on both of them. Let confusion reign! :-) Good point to both!!! Maybe the admins can combine them into one for us. Hint Hint!!!! Quote Link to comment Share on other sites More sharing options...
G-E Posted September 22, 2014 Share Posted September 22, 2014 (edited) I'm sure using slip-on rotors would help mitigate if not alleviate much of the problem. The isolated stresses you're putting on each stud (edit: using a bolt-on rotor) will radiate to those valleys on the back side around the bosses... As stiff as the wheel is or isn't, adding a rotor which is a solid flat layer would help diffuse those stresses. It is also very possible the heat stresses from the rotor on the other bosses plays a role in the long term fatigue rate, something that would also be diffused with a slip-on rotor... Edited September 22, 2014 by G-E Quote Link to comment Share on other sites More sharing options...
Phantom Posted September 22, 2014 Author Share Posted September 22, 2014 (edited) Ken, I know a gent on this site down in California (CHEQUERED FLAG JOE) has been trying to breathe life back into MM. You might PM him here on the site about it. Edited September 22, 2014 by Phantom Quote Link to comment Share on other sites More sharing options...
wheelman Posted September 22, 2014 Share Posted September 22, 2014 I'm sure using slip-on rotors would help mitigate if not alleviate much of the problem. The isolated stresses you're putting on each stud (edit: using a bolt-on rotor) will radiate to those valleys on the back side around the bosses... As stiff as the wheel is or isn't, adding a rotor which is a solid flat layer would help diffuse those stresses. It is also very possible the heat stresses from the rotor on the other bosses plays a role in the long term fatigue rate, something that would also be diffused with a slip-on rotor... That's an interesting idea, I wonder if anyone has figured out a combination that will work on the Z spindle. Whats got me the most perplexed is I ran essentially this same setup for years with no problems. The biggest differences are Hoosier A6s vs. Kumho V710s (on the same rims), and vented front rotors vs solid front rotors (both of which bolt to the hub in exactly the same manner). There is a HUGE difference in the grip levels between the 2 tire brands but I'm having a hard time accepting that we're producing enough force to actually break the hubs. The one aspect of the site where we autocross that might be the key factor is the courses transition on and off a banked oval track and most of the time it's the right front corner that hits the transition first, plus we're usually carrying a fair bit of speed at those points. BTW: Smart phone G sensors we've had in the car all season have showed lateral G forces as high as 1.8 with 1.4 - 1.5 steady state and linear as high as 1.3-1.4 while braking and between .8 and .9 accelerating. I have no idea how accurate these readings are so take them with a grain of salt. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 22, 2014 Share Posted September 22, 2014 If you didn't want to swap out the brakes, a wheel spacer should have roughly the same effect. Quote Link to comment Share on other sites More sharing options...
wheelman Posted September 22, 2014 Share Posted September 22, 2014 (edited) Jon, You mean put a wheel spacer between the hub face and the back side of the rotor hat? That could work, then it would be a matter of finding a rotor with the correct stud spacing and backspacing. Any ideas of ones that would be contenders? Edited September 22, 2014 by wheelman Quote Link to comment Share on other sites More sharing options...
G-E Posted September 22, 2014 Share Posted September 22, 2014 The Z31's prior to the 87+ turbos had the same kind of bolt-on hubs with the same kind of valleys between bosses, and while I've never heard of one failing on a road car, that's not really the issue afterall... I did however make a big brake kit that converts it to slip-on, I made some really tall hats for this purpose, you can see just how tall in this pic (32mm thick ring): That would go a looong way towards eliminating flex, not only because of the extra 7mm of aluminum, but that it's part of a cone (unlike a wheel spacer).. If you ran 17's I could send you a set I had opened up to 73mm bore... Quote Link to comment Share on other sites More sharing options...
johnc Posted September 22, 2014 Share Posted September 22, 2014 You might just be at the material strength limit for the hub, the steel wheels might be flexing too much, or the wheel might be incorrectly seated against the hub face. I ran 16 x 10 Kodiak wheels with 275/45-16 with Hoosier A6 and R6 on the Rusty Old Datsun (2,150 lbs without driver). Never had a problem and those same hubs had 10+ years of autocross and track days with 15 x 8 Monocoque wheels and various DOT-R 225/50-15s. Car weighed anywhere from 2,290 to 2,410 during that time period and pulled from 1 to 1.6G lateral for the 14 years it raced on those same hubs. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 22, 2014 Share Posted September 22, 2014 Jon, You mean put a wheel spacer between the hub face and the back side of the rotor hat? That could work, then it would be a matter of finding a rotor with the correct stud spacing and backspacing. Any ideas of ones that would be contenders? No, I meant if the idea was to spread the load across the face of the hub more evenly, a simple wheel spacer would do that probably about as well as a slip on rotor hat. With Z wheel spacers, you have to be a bit careful. I've bought several sets and never had them work out of the box. The cheapo ones from the auto parts store had a center hole that was about .005" too small. Such a small error that I couldn't figure out why the wheels wouldn't balance, but also couldn't figure out that they were too small. Finally found the problem when one started cracking. Later I got some nicer lugcentric ones from colemanracing.com and the pilot was way too small so I had a machinist turn them on a lathe to open them up. Quote Link to comment Share on other sites More sharing options...
G-E Posted September 22, 2014 Share Posted September 22, 2014 You might just be at the material strength limit for the hub, the steel wheels might be flexing too much, or the wheel might be incorrectly seated against the hub face. I ran 16 x 10 Kodiak wheels with 275/45-16 with Hoosier A6 and R6 on the Rusty Old Datsun (2,150 lbs without driver). Never had a problem and those same hubs had 10+ years of autocross and track days with 15 x 8 Monocoque wheels and various DOT-R 225/50-15s. Car weighed anywhere from 2,290 to 2,410 during that time period and pulled from 1 to 1.6G lateral for the 14 years it raced on those same hubs. I'm sure it's exacerbated by the steel wheels he's running, and a stiff solid-core aluminum one like a weds or rays wheel would help No, I meant if the idea was to spread the load across the face of the hub more evenly, a simple wheel spacer would do that probably about as well as a slip on rotor hat. I disagree, just like the egg shell is incredibly thin, it's strength comes from the shape, a 7mm thick rotor hat will be far stiffer than a 10mm flat spacer, a situation that wouldn't change until probably >20mm bolt-on adapter... Quote Link to comment Share on other sites More sharing options...
tube80z Posted September 22, 2014 Share Posted September 22, 2014 Ken, Your wish is my command, at least for the merge. That last time, and it was a long time ago, I ran an autocross with the circle track to infield it felt like hitting a curb when going onto and off of the banking. I think you said that was the loaded side, which sounds like it's loaded up with a lot of lateral force and run across the junction it may be too much for the hub to hack. I don't know about your steel wheels but when I run my diamonds really hard I could see a wear pattern on the hub face. Do you see anything like that on yours? I'm thinking the easy solution is a 5-lug hub so there is more clamping against the wheel. If you have ARP or similar studs and upped the torque it might be harder on the hub with a flexible wheel. All conjecture but not sure how you really test this one out without a lot of fancy equipment and/or FEA on part models. Cary Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted September 22, 2014 Share Posted September 22, 2014 I don't know what brake kit you are running, but it seems the easiest thing to do is to switch to a 280z hub, which doesn't have the material removed between individual studs. I had a supply problem once on 240z hubs so I ran a 240z hub on one side and a 280z hub on the other. I just had to bolt a 280 hub to a 280 rotor and a 240 hub to a 240 rotor and the caliper lined up fine. I think you said something about having a spacer machined to allow you to switch-that still sounds like the cheapest/easiest solution. Quote Link to comment Share on other sites More sharing options...
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