1995 Newsletter Archive

At the March National at Road Atlanta, I unfortunately got a chance to test the A/S roll cage design.  I want to comment on its integrity, especially since there are folks calling me all the time discussing their new A/S cars under construction.  One only learns to truly appreciate a roll cage design after one has "tested", and hopefully survived, a big accident.

At Saturday morning qualifying, I made a radical brake bias adjustment which caused me to go flying off the entry of turn 3 at Road Atlanta on my second qualifying lap.  I shot straight off the track, down the wet embankment, through the end of a guard rail/tire barrier, took out a tall TV-camera stand (which was fortunately unoccupied), then jacked sideways into the trees.  The trees did not move (needless to say <g>), and the resulting instant deceleration caused a major attempt of the car to become "one" with a large diameter tree, right in the driver's door behind the sideview mirror.  You've heard of 0-to?60 times?  This was 60-to?0 in a few feet.  The result for me was two fractured ribs and a double fractured lower left leg, neither of which I noticed as I hauled myself out of the passenger window and onto the ground.  (Amazing what you can do before the pain sets in).

When I got to the Lanier County Hospital, the ER nurse took one look at the ambulance from Road Atlanta and said "Awright... what is it this weekend.... cars or motorcycles?"

Since then, my left leg has required orthopedic surgery to correct a tibial plateau depression fracture, which has healed much slower than the broken fibula right next to it.  The leg surgery started a three-month clock of no weight bearing, which essentially means three months of using walkers, crutches, and a wheelchair until any weight can be put on it.  The two cracked ribs took about eight weeks to heal.  At eight weeks post-surgery, I started clutch therapy by sitting and pumping the clutch on my street car for physical therapy.  At ten weeks, I started driving the clutch street car with a range-of-motion brace on my leg for stability.  Soon all will be well again.

For those few readers that need a description, basically an "A/S-style cage" is an eight point cage meaning: a rear main hoop with two rearward braces, and a front hoop with two forward braces, often to the firewall.  Also, the driver's door inner panels, glass, and winding mechanisms may be removed to allow the minimum of two side door bars to go out and be positioned at the door skin.  Any connecting bars within the cage (like a dash bar) can be added as you desire.  These last two points are very important, as I believe they saved my life.  Please read the below and consider these comments seriously when you design your safety equipment.

Safety equipment lessons learned:

  1. The driver's side door bars, which were designed to bow out from the front hoop, travel along the inside of the outer door skin (NASCAR-style), and then bow back in to weld to the rear hoop, did a fantastic job and provided the additional crush space to save my body and possibly my life.  Whether you get impacted by a speeding tree or another car, those side bars definitely need to be out there by the door skin.  As a side benefit, that also makes ingress/egress much easier for the driver also.  Weld some small vertical connecting bars between the door bars to increase strength.
  2. The horizontal bar across the dash, connecting the downtubes of the front hoop, was one of the critical players, as it kept the sides of the front hoop from collapsing in on me.  The front hoop and all connected bars, were folded in by the impact just below that horizontal dash bar.  This is the single most important item that saved my life.  Those front down tubes need to be braced across the dash.  Otherwise, there is nothing to keep them from collapsing inward in a side impact.
  3. My left leg was broken by the forward brace of the front hoop that runs to the firewall, despite a wrapping of high quality roll bar padding.  Believe me, at those impact speeds, blunt trauma breaks bones too.  That brace is VERY important in a front impact to keep the driver's feet from being crushed in the footwell, but you need to consider padding that and ANY other bar that can possibly impact your legs in other collision directions.  Recommendation:  Sit in your driver's seat and flail your arms and legs around like a electrocuted ragdoll.  Anything you hit is a danger to your limbs in an accident.  Particularly note and pad any sharp edges you encounter.
  4. My Butler-Built seat did a superb job. I had very little neck pain whatsoever, due to the right side helmet wing that caught my helmet and prevented what could have been a paralyzing side-to-side neck snap/whiplash injury upon such a heavy side impact.  (The left side of my helmet was braced by the roll cage padding).  My two cracked ribs are because I am such a skinny guy, and the little padding between my rib cage and the smooth chest plate of the seat was too thin.  I would add extra padding on the sides for we skinny guys.  The seat did a terrific job in holding me in place, and in fact showed so little distortion that it looks as good as new.  Use what the Winston Cup drivers use - they all use ButlerBuilt.  The next time a Winston Cup NASCAR race is on TV, look behind the driver's heads, and you will see the ButlerBuilt name on the headrest.

 Note:  When ordering a ButlerBuilt seat (1-800-621-SEAT), you can order stock sizes or have one specially made to your measurements like a driver's suit.  They can send you a measurement brochure with the directions.  The most important measurement to get correct is the measurement from the bottom of your armpit to the table top (#2).  You must relax your shoulder and not overestimate this measurement, else your seat will be made with chest wings so high that your arms will abrade during driving.  The seats are double-walled aluminum with a geometry to the space between the walls that greatly enhances the strength.  The aluminum welds are the finest I have ever seen.  (By the way, these are not expensive seats.  I believe even their custom made seats are still less than $500).  Options to be ordered with the seat are:  a set of front and rear mounting rails (#2200), a rear seat back bracket (#2215) that can brace the seat back to the roll cage, and most importantly, a right side Energy Impact System head support (#2218).  Also, if your driver's footwell floor is getting hot enough from your headers to burn your heel, you may want to consider the ButlerBuilt Thermal Barrier Mats available in different sizes.  ButlerBuilt is located about ten minutes from Charlotte Motor Speedway, if you are ever in the area and want to visit.

Side Note:  I think at this point that I would advocate strongly for the option of using A/S style cages in all IT cars.  The door bars to the outer skin, the dash bar strengthening the front hoop, and the Butler Built seat combined to allow me to live long enough to write this note.  I will once again agree with the folks that say that fiberglass seats do NOT belong in race cars.

Have fun out there, but build safely and plan for the worst.  Brown days really do happen.

- Charlie


If I had not had my left foot planted so firmly on the clutch, I would have saved my leg.  You know the "both feet out" rule that is taught in many driver's schools?  It is a good rule but needs a modification.

The rule states that when you start to spin out of control, put both feet out, on the clutch and brake HARD.  Then, when the car stops spinning, the engine will hopefully still be running and not stalled, so you can get the h*ll out of the way of oncoming traffic and off of the track, for example, if needed.

The modification that needs to be taught, is that after all is lost and you are heading towards something hard, do what the NASCAR drivers do. An in?car camera showed recently what Jeff Gordon did just before hitting the wall. Pull all your extremities back in close, cross your arms like a fetus, and pull your legs up close.  If I would have had my feet off of the pedals at impact, I would not have earned this double fractured leg that required surgery to correct.

The other big recommendation is to get your death grip off of the steering wheel, as that often breaks the wrists of the driver at an impact snap.  Fortunately, I reflexively pulled my fingers off the wheel in my accident and only had my palms touching the wheel at impact.


Some other incidents that have been reported recently deserve to be discussed here.  It is always important to look at your racecar from the standpoint of a potential fire.  Practice your fast egress (meaning getting out in a hurry).  Can you get your window net unhooked in a hurry?  Look around the inside of your car for potential problems.

  1. One interesting but costly episode recently involved an overturned racecar.  Unknown to anyone, the fuel system (carb?) had leaked gasoline and accumulated a puddle on the underside of the hood of the upsidedown car.  When the workers rolled the car back over onto its tires, the raw gas fell onto the hot exhaust headers and immediately started an underhood fire.  Moral from this story?  Make absolutely sure that your kill-switch truly kills all power including your fuel pump, and get that switch turned off as soon as possible after an incident.  Remember this incident if you are confronted with a similar situation involving rolling your car over.  Carburetors also have been known to leak out the tops when inverted also.
  2. Check for open holes through the firewall, especially around the driver's feet.  Any hole could allow the passage of flames from the engine compartment to the driver's legs in a hurry.
  3. Melting of the shift boot and/or smoke out of the hole are often signs of an engine fire.  Simpson sells Nomex boots for your shifter, and could be something to consider.
  4. Make sure that your onboard fire system has no kinks or crimps in the lines.  I recently had to replace my underhood line after I noticed that the nozzle had been bumped while working on the engine, and crimped the metal line.
  5. Recommended locations for your two nozzles are one underhood facing the carburetor area, and one separating the driver from the fuel cell.  Don't place a nozzle so close to your body that you get frostbite from the direct discharge.

(The following was sent to me from a driver who recently survived a horrific accident during practice at Lime Rock.  Unfortunately, practice days at Lime Rock group race cars and street cars together in the same run groups, which can be dangerous since some of those street cars are driven by folks who can be wildly unpredictable on a race track.  Not that race drivers are ever unpredictable, but.... at least if the practice groups are separated into street cars and race cars, then you have some reasonable expectation of speed familiarity.  Anyway, the following report points out some more very important items to keep in mind when building your AS car.  Look your car over and think about these comments.)

Charlie asked me to write a few lines on safety since I now have first hand experience testing safety equipment after my AS Camaro got rolled a couple of times recently.  I'm not an expert but here are my observations.

1.  Cage.  A strong well-designed cage with first rate materials is a must.  Two bars in the door on the driver's side out as far from the driver as possible.  The cage should be welded securely at all locations and braced laterally and horizontally where possible, with a cross bar in front of the driver supporting the front down tubes.  I had a bar from the upper hoop behind the driver down to the floor mount passenger's front.  I believe this was very important in keeping the top hoop from collapsing on me while I was upside down.  Plenty of roll cage padding anywhere you think there is the slightest chance of contact with you.  When you're rolling around, arms and legs are moving whether you try to control them or not, and the cage can be pushed towards you.  If you could see my car, you would have instant respect for the value of a good cage.  I walked away but would have been seriously injured with a typical showroom stock style cage.  Showroom stockers take note.

2.  Seat:  Charlie is right, the fiberglass seats are not good enough.  Mine broke on a line from the left armpit to the top of my right shoulder.  It broke going forward toward my head and neck area.  Enough said.  My Butler seat order was placed today.

3.  Compartmentalize the fuel cell.  I was submarined in the back by a Porsche.  I had a well made metal compartment housing the fuel cell which was also in the standard metal container.  The compartment took a big hit, the fuel cell is fine.  The extra protection is worth it.

4.  Face shield.  I didn't have mine on but during the accident there was a lot of broken glass, dirt, grass, dust, and miscellaneous car parts flying around.  When they pulled me out I was covered with it.  Nothing hit my eyes or face directly but it could have.  Just lucky this time.

5.  Seat belts, tight and new.  My new Simpson five point did the job and kept me in place.  Maybe an older, less expensive one would have failed, who knows.

6.  Fire extinguisher.  I have always driven with the safety pin "in".  Not a good idea.  Have it all ready to go.  Pulling the pin is an extra step when time is of the essence.

7.  On/Off switch.  Have it in a place you can get to easily.  I had to reach for mine which was inconvenient.  In this case it was irrelevant, since the battery left the car early on.

For some, we don't think much about safety until we need it and then it's too late.  I did some things well, I could have done some things better.  For the record, I walked away but I was lucky and it could have been worse.


Not to be forgotten, carbon monoxide (CO) is a byproduct of this hobby and can be quite profound in its effects, ranging from confusion and nausea to death from asphyxiation.  We all know that you don't do things like run your car's engine in a closed garage, but what about CO effects on the racetrack?  If you follow NASCAR racing, you have seen several incidents of drivers being affected by exhaust fumes and CO in the driver's compartment.  Read the following, and then go look at your racecar again with the potential for CO poisoning in mind:

(The following was posted by Steph Weiss originally on both the wheel-to-wheel internet discussion group and Compuserve, and is reproduced here with her permission:)

As Kurt got dressed for the AS race at the Lime Rock National on July 1, he took a few big swigs of Gatorade and asked me to keep it close at hand in case they impounded all AS again after the race. Kurt reminded us that he only needed to finish 15 of the 30 laps (to get credit for his license renewal) so if he was in last place and the car was overheating or having other problems, he'd likely stop early.

Kurt had a good start and managed to stay with Rick DiIorio and eventual second-place finisher George Smith Jr. (in a Camaro) for a few laps before Kurt's year-old tires started to fade and everyone pulled away. In retrospect, Kurt recalls that by halfway, he was feeling a little nauseous and was getting a headache, but nothing that concerned him enough to pull into the pits.

On the video, you can see the steady progression from aggressive, confident driver to one who is terribly confused. Watching from the pits, Dan and I were also a little confused. About three laps from the end, Kurt came down the right side of the track and nearly put two wheels into the dirt, which I thought was a little overdone just to allow a GT?1 car to pass on the left. The following lap, he did the same, and was moving so slowly that Dan and I both expected him to pull in. Instead, he kept going, two wheels in the dirt, while a block of cars went by, two and three abreast. On the checker lap, again, he was two wheels in the dirt and slow. I was sure there was something wrong but assumed it was the car. I couldn't see what the flaggers around the track could see and were calling in: #98 yellow and blue, driving erratically, his head bobbing and shaking.

The video would make an excellent Mothers Against Drunken Driving commercial. [Charlie Vaccaro, a former ITA competitor and now in GT3, said that if he'd had lights and a siren on his RX3, he'd have pulled Kurt over for DWI.] Kurt is all over the track -- and the dirt -- his head flopping around wildly. Several times, he shakes it violently, as one does when trying to stay awake. On the checker lap, he is literally asleep from Big Bend to the left-hander, where he drives off, driver's right, and spins, his head down. (Amazingly, something clicks in his subconscious, and his arms countersteer.) His head bobs forward onto the steering wheel, where he rests, unconscious, for 55 seconds. [The flaggers have called for a safety car, but in all this time, no person appears at his car.] Then something revives him at least a little, and he lifts his head. His hand reaches for the key, and as you watch, you shout, "No!!" You wish that the battery were the old dead one or that the starter would fail. But he fires it up, and takes off. Race direction, thank God.

Back in reality, Lorinda Cherry runs down from the tower. "You might want to have some towels and water ready for Kurt. He just spun on the cool-down, and we think he's suffering from heat exhaustion." I thank her and suggest that it's probably just his tires (of course, I haven't seen the extent of what's been happening on the track).

As he reaches the pits, he nearly misses the entrance and nearly collects the barrier. I step into a pit box, and he pulls in. "What's wrong?" I ask through the passenger side window. I cannot hear his soft reply. I go to the driver side and ask again. "I was overcome," he whispers. He is glassy-eyed, staring straight ahead, uncomprehending. "Get some iced towels," I shout to Dan, who runs toward the tech shed for the towels. A pit marshall comes over. "Is he OK?" he asks. "No," I reply. "They're coming from medical," he responds. [The safety car had been dispatched to station 4.] I help Kurt take his helmet and stuff off. Dan arrives with the towels. I put one on Kurt's neck, and he doesn't even flinch from the cold. Wilson Wright brings bottles of water. Two fire & rescue people arrive and help Kurt from the car. He collapses in a heap; Danny Fisher and Fran Dance leap the pit wall from impound to help. Danny is pulling Kurt's suit off when the safety car arrives. Danny nearly slugs someone who suggests cutting the suit off (the suggestion also revives Kurt, if only slightly). The rescuers get his suit off as the ambulance pulls up. They put him on a stretcher, cover him with iced towels and start an IV. He has no idea who or where he is. He is off to the hospital. Dan, Gerry and my parents will load the car on the trailer. Frank drives me to the hospital.

When we arrive, Kurt is joking with the ambulance driver, so I know he is OK. I fill out forms for a few minutes, then get to see him. We grin at each other for a while and gab some; he insists that he didn't ever spin, that he didn't hit anyone (he did both; the video tape really was an eye-opener for him) and that he doesn't need the IV because he feels fine. The doc wanders in and asks some questions, during which Kurt mentions that his eyes were stinging during the race. The doc's eyebrows go up. "Why don't I just draw some blood and check your carbon monoxide level?" he asks. Kurt is agreeable, and blood is drawn. Moments later, the doc rushes in. "If you had any other health problems at all, you wouldn't be staying here [in the ER? in this small-town hospital?] with a CO level like this," he says. The number on the sheet is 33.7 percent COHb. (According to Consumer Reports, a level of 50 percent is "often fatal." A heavy smoker's CO level is 6 to 7 percent, the doc says.)

Three-and-a-half hours later, the re-oxygenated Kurt (looking much pinker) was released from Sharon Hospital. The doctor's instructions: "Rest. Cool liquids. DO NOT GET BACK INTO THAT VEHICLE UNTIL EXHAUST IS FIXED."

A couple of hours later, we watched the video in silence. Kurt made a list of people he'd have to apologize to; we watched several laps repeatedly, trying to figure out whose reddish paint is on the passenger side door (George Smith Jr., we think).

The exhaust, per ASCS D.1.e.1, ends behind the driver and is "directed away from the car body" toward the back of the car, where, we now believe, the car's aerodynamics suck it right into the car through the fuel cell cage. Kurt drove the car in the same configuration during three -- shorter -- regional races last year without a problem. Did the heat contribute? The length of the race? Both?

What should/could have been done to stop him two laps earlier, when -- at least on the video -- it is pretty clear that he is having a problem? Would he have even seen a black flag? We all doubt it. I kick myself that we hadn't yet put the radios in his car.... that we didn't put in a better ventilation system.... that he didn't take the time to re-think the exhaust....

And I thank God that he didn't hit a wall, injure another driver or succumb more disastrously to the fumes.

Steph Weiss, #18 ITA BMW 2002tii
Div. F&C, Stephentown, NY

How did the CO get into the car?  Steph suggests that it may have been leaking around the fuel cell.  As Steph says, "We hadn't totally sealed the cover around the fuel cell, so I'm pretty sure that's where it came in. But we honestly don't know....  In fact, there were at least two other AS Mustangs at the Glen whose exhaust went straight back and terminated before the rear bumper. Kurt said they're not exactly the same as his was, but still.... There's a potential there."

There were other important points made by messages responding to Steph's story:

(1)  Remember to seal ALL the holes in the floor of your racecar.  Mark Silverberg made the following very important observations about this problem:

"Just a few observations about Carbon Monoxide and Closed Cars.  A race car environment is worse for CO for several reasons.  First Although CO is lighter than air it is just barely lighter (CO = 1.25 kg/M3  Air = 1.293 kg/m3) - thus once it gets in the interior it is not likely to leave - I. E. desire to rise is not that great.  Air currents in interior will tend to mix it in - not let it rise and escape.
Interior of car by nature will run at a lower static pressure than exterior because of flow of air past open side windows.  This will tend to draw air out of the interior (good) but suck it in from another place (good or bad depending on what that place is).
What you want to avoid is having a path from a location of high CO concentration and high pressure to the low pressure interior.  While you might initially think that sealing holes in the floor aft of the driver is not important it still an area from the higher pressure exterior to the
lower pressure interior.
When we thing about our experiences this makes sense.  How many times have we seen a race car driving with smoke in the cockpit and very little flowing out - then when the car stops the smoke starts to pour out after the pressure equalizes.
What can we do to help our cause:

  1. Increase interior static pressure.  We have all seen the air scoops by the windshield pillars on Trans Am and other GT Cars.  We assume they are for driver cooling - but it will also increase the static pressure in the interior and we can pick and choose our pressure source.
  2. Check interior of cars for flow paths - EVERYPLACE - not just in the firewall
  3. And of course check out exhaust systems.
It should be noted that about a week before this incident we had a driver complain about being black flagged for a loose exhaust.  I don't blame him - I would have complained too!.  That loose exhaust could have been a CO danger - not very likely, but theoretically.  The point is that we all have to take initiative to avoid future incidents with CO or SCCA may get even more strict on minor exhaust system malfunctions.
It is extremely unfortunate that the incident at Lime Rock occurred.  I think we all realized that it could have been any of us.  I hope my comments have helped and that we all take a little closer look at our cars.
Mark Silverberg
Chassis Engineering / Frames & Mounts


Recently, there were many excellent internet messages of hints for preparing and attending your first SCCA Driver's School.  I want to compile them into a story for the next newsletter, but I must get permission from all the authors first.  Many of the hints apply to ongoing racing efforts.  Steph Weiss, noted IT BMW driver and hotshoe, suggested the following:

  1. RELAX! Don't white-knuckle the steering wheel!
  2. Have a predictable car. Kurt has touched everything on my car to ensure it won't start on fire, fall off, stick on full throttle, roll over, bounce off the track, etc. (been there, done all that)
  3. Be organized about your race prep; don't wait until the very last minute to do things. (This is kind of a corollary to both #1 and #2.) You'll feel more comfortable with your car and more relaxed if you have a checklist for things like torquing the wheels, adding gas, checking oil, tires, etc., and get those items done early.
  4. Get lots of seat time. I decided this year that I would never get fast doing six races a year, which is what I've done for the past couple of years. When I was at my peak, I was doing 15?20 BMW driver schools a year! No wonder I was slowing down instead of speeding up!
  5. Have confidence in yourself!! If you go in believing you'll be in the back of the pack, then you will be. If you believe... then things might just happen for you!
  6. Go ice racing! Yes, we go head-to-head on frozen lakes. We ice race an RX?7 and almost everyone else has front-wheel drive. Here's how Kurt explained the skills I learned: not to panic when the car slides and not to be tentative in traffic.
  7. Look way ahead. The closer you look in front of your car, the faster everything seems to be whizzing by and the less time you have to correct your actions.
  8. Don't copy the mistakes of slow drivers; learn from the fast guys. I still have a really hard time with this one, especially during qualifying. If you keep dicing with the same guys all the time, you'll never have a shot at the Bigger Dogs. Don't be afraid to pit or take a slow lap to get away from people who may be slowing you down; it doesn't mean you dislike them.
  9. Get everything (brakes, shift, etc.) done early so you can get on the gas sooner.
  10. Be absolutely snug and comfortable in your racing seat. I got camlock belts with pull-down straps this year (since I had to replace because of the new GCR requirement), and it enables me to really get the belts snug. I LIKE that.
  11. Have predictable tires. I've been using BFG Comp TAs, starting at full tread depth and running them bald without any problems. Some (including BFG) say I'd be better off shaving them but then I'd sacrifice the longevity.  (Remember #4!)
  12. Remember that you're in this to have FUN. Winning is nice, but the main thing is to enjoy the sport of it. Don't expect to improve every time on the track, but see if you can learn something every time you go out.
  1. Don't forget to torque your lugs before you go out.  It seems like every race weekend, I see someone having their session, if not weekend, ruined because this was overlooked.  I have seen formula cars and sedans flip, roll, lose wheels, bend metal, etc., etc. all because of this.   Forgetting to your torque wheel nuts is dangerous to me too!  <grin>
  2. Get your belts and harness adjusted before you get to the track.
  3. Check for loose tools under the hood and on the floor.  Only in the past few years, have I stopped going out on the track with a screwdriver or wrench rattling around on the floor.
  4. Don't brace on the steering wheel.  Your forearms, back, and shoulders need better support.

(Recently, there was an interesting interchange on Compuserve about rear axle shaft failures, that I will reproduce here, having obtained permission from all of the three writers:  Brent Olsen, Bruce Carr, and Bob Burns:)

Brent:  "My research into this area indicates that the problem area on stock axles is the flange outside of the bearing.  The most likely reason for the breakage there is caused by the chassis bottoming out on top of the axle tube. I have looked into other axles for my AS car and was almost sold on a set of Summers Brothers until one of my competitors broke one this past weekend.  The axle broke inside the axle tube along the axle shaft.  I buy a stock set every year from my local dealer for $115 each then have them checked for cracks and shot peened.  So far so good..."

Bruce:  "True on most stub-axle type assemblies (why FWD cars have such high spindle failure rates), but highly unusual to have failures here on a properly machined rear axle shaft. A more serious problem with the C-clip type axle is that the original-style axle bearing (a straight roller bearing) uses a hardened and finished area toward the flange of the shaft as the inner race of the bearing. Because the bearing is harder than the shaft, the bearing eventually wears a quadrant into the axle shaft. The first sign of this on the street is diff fluid leaking out on the brakes. The first sign on the track is sometimes an axle shaft that fails at that point (just outboard of the seal riding area).

The other tradeoff with this axle-as-inner-race design is shown by the failure you mentioned. To wit:  >> until one of my competitors broke one this past weekend.  The axle broke inside the axle tube along the axle shaft.<<

That's the problem. See, the shafts have to be reasonably soft so they won't break from torque and banging about, but hard enough to be strong and not twist like wet noodles. So on the street, the tradeoff is simply to err on the too-soft side because big HP on the street still isn't much in terms of the axle's ability to handle it. But when you do have the HP or are in a competition situation, you really want the tradeoff to go the other way a bit. So racing axles are harder than straight street axles, but by what amount can vary widely. But what happens gradually over the life of any high performance application axle shaft is that it twists. Sometimes slowly, inexorably. Then, eventually, the twisting encounters an imperfection in the axle shaft material or it goes out of true. And then that's all she wrote...it breaks like your friend's did. Just a day in the life of an axle shaft.

Humble Suggestion: do like the drag racers do and paint a straight line on the shaft. Pull the shafts partway out once in a while (don't let the splines cut the inner seal!) and replace the shaft when the straight line looks like it's going to become a barber pole.

An additional humble suggestion: For road racing axle shafts, I would try Moser Engineering first. Summers Brothers and Mark Williams are excellent suppliers, but their primary customer is a drag racer and their axles are really engineered to use c-clip eliminators. The metallurgical needs of axle shafts for drag racers vs. road racers is a little different, and Greg Moser concentrates more on the street rod end of the business. Street rod demands are fairly similar to the (relatively) low horsepower road-racing situation in AS. And last I knew, Moser would make up any axle shaft you want, you just tell them what shaft you need and what you're using it for."

Bob:  "What happens to an axle shaft is pretty complex.  Much more than just simple twisting.  The ultimate torsional stress at which a shaft will deform is much higher than the stress at which the shaft will fail in the real world.

The torque delivered to an axle shaft doesn't come smoothly.  Imperfections in the ring and pinion gears, velocity changes due to driveshaft misalignment, imperfections in the transmission gears, and cylinder-firing pulses from the engine all result in an irregular application of torque to the shaft.  The result is that the torque varies at a fairly high frequency (5, 10, 20 Hz depending on the source of the variation).  This constantly changing torque contributes to cyclic torsional vibration in the shaft and cyclic fatigue due to that vibration.

The problem at the joint between the flange and the axle is due to a cyclic bending of the joint.  If you take an axle shaft which isn't turning and apply a side load to the wheel, the flange-axle joint bends.  But as you turn the axle, the bending is distributed around the axle.  When the axle is in the 0 degree position, one side of the joint is in compression and the opposite side is in tension.  As you turn the axle to 180 degrees, the tension/compression forces reverse.  Now, rotate the axle at 1500rpm with that side load applied. Again, we have a cyclic fatigue situation.

Localized hardening, like to increase the wear resistance of a bearing race or as a result of welding, or the addition of a stress riser, like due to a section change in the shaft or due to a snap ring groove, are like magnets for cyclic fatigue.  The possibility of failure due to fatigue can be alleviated somewhat by shotpeening the shaft in the danger areas, but you can't eliminate cyclic fatigue completely.

You are quite correct that the design of an axle shaft for drag racing is quite different from the design for road racing.  The drag racers are more interested in ultimate torsional strength so that the shaft won't break under a severe, single application of torque.  The road racers are, or should be, more interested in fatigue due to torsional vibration or cyclic bending.

I used to break transmission shafts for a living.  Destructive testing was a fact of life in our lab.  There weren't many parts in a truck or army tank transmission which we couldn't' break.  When, not if, a shaft broke, we always looked for stress risers or hard spots as sources for the failure.  Stress risers are probably the biggest problem.  Snap ring grooves, oil seal grooves, oil holes, splines, etc., all look good on paper to the design engineer, but they raise red flags to the fatigue analyst.   P.S.  We had a sign in our lab which read "Do something destructive today, our business is failing."


Be very careful when tightening the two bolts that hold the clutch cylinder onto the bell housing.  The clutch cylinder is only plastic and you can easily fracture or crack those mounting tabs if you overtighten.  Two recommendations:  First, add to your list of pre-race check items, a check of the clutch cylinder mounting tabs to see if the bolts are secure and the plastic ears are solid and not cracked.  Second, get a spare cylinder to add to your traveling box of spares.  Two part numbers apply:  1410-5757 will get you the entire clutch hydraulic kit in a box, including the reservoir and lines, all ready for complete installation.  A cheaper and faster alternative, is to buy only the clutch cylinder itself, which is hard to see in the parts catalog, but is part number 1007-4135.