* BIG off at the track - and a torque tip -

[Craig 930 RS]

Had the bolt which goes through the ERP bump steer setup break.
In a BIG way.



Going through turn 9 (at Pacific Raceways in WA State)
Approx 90 mph and at full throttle the right (relatively unloaded) bump steer bolt broke -- quite possibly due to overtorquing.

Mid corner the steering got lighter - and the car just went straight. Very little control. Just tried to keep it straight. Right through the gravel, like a shot. Bounding, bouncing, ripping and scratching at the underside of the car until the left side caught and spun me around in a 360. Heading towards the wall, both feet in.

Point of breakage was way up the track in the pic below. I ended up where I took the picture below.


I have never seen a car spin in this corner and NOT hit the wall.
Many have been a total with at least some injuries.

In the words of the track event chief:
"You need to go buy a lottery ticket tonight"
-----------------------------------------------------------------
Probable cause? Over torque of the bump steer bolt.
A metallurgist who was driving at the track said that the bolt had been fractured for quite some time - and that the portion holding it together consisted of only the center 1/4 of the bolt.



She went home in a friends' trailer.


Got to drive his 440hp 930 - on Hooisers - home


Very lucky. Watch that bolt torque!

[alf]

Craig
Glad to see you are ok. Loosing steering on the front straight nerve wrecking. I have seen 2 cars hit the walls there.

alf

[Chuck Moreland]

Scary.

In pic 1 it looks like the bolt sheared at both ends. It looks like there is a stub remaining in the tie rod, and obviously another holding the nut to the steering knuckle.


Why do you think it was over-torqued? Did you do the installation?

[Craig 930 RS]

"Why do you think it was over-torqued? Did you do the installation?"

It only fractured at one point. The 1st pic is of the 1/2 bolt still in the strut. Hammered it out.

A metallurgist who was driving at the track said that the bolt had been fractured for quite some time - and that the portion holding it together consisted of only the center 1/4 of the bolt.

The early fracture points had grease and dirt on them - it was evident even to me that it had been that way for some time.

I didn't do the installation.
---------------------------------------------------------------

It was scary.

Had no options, very little control. Car ran wide by itself, I took a mental inventory of what my sensory inputs were telling me -- and nothing made sense.

Equipment failure is one variable that makes it the scariest of all.
WTF? just about describes what goes through your mind

[Chuck Moreland]

Okay, but why does that imply overtorque? The origianl fracture may have happened from impact, hitting bumps, overstress, etc. It's not unusual for a crack to develop and grow over time, eventually leading to failure.

[304065]

That ERP bolt is a problem waiting to happen, anyway.

Mounted in single shear like that?

Gotta be a way to wrap around the steering arm in double shear.

[Craig 930 RS]

To the metallurgist, it had all signs of overtorquing.
He is the expert, I am not -

[89911]

Enough of a reason to avoid that system. I have never heard of the factory ball joints failing.

[Craig 930 RS]

"That ERP bolt is a problem waiting to happen, anyway.
Mounted in single shear like that?
Gotta be a way to wrap around the steering arm in double shear"

Our thoughts (track guys that is) exactly. I thought the ERP stuff was beyond reproach and I honestly haven't heard of another failure like this. But, the design makes little sense - huge side forces acting upon the bolt.

Any other options??

[304065]

I have never heard of the factory ball joints failing

Well, the factory ball joint is mounted in single shear, but it's basically right against the steering arm. When you lower the suspension and not the rack, you extend the bolt between rack and steering arm, which multiplies the force by the distance you extend the bolt.

[Zeke]

Originally posted by Craig911

Any other options??

The guys who use raised spindles bend the arm. That scares me a little, but it is an option.

[89911]

Were you having a problem with the stock setup? My car is pretty low, see's mostly track, and I can't say I've had any issues with the steering, or bump steering effect. Maybe the simpliest solution is nothing.

[Chuck Moreland]

Originally posted by Zeke
The guys who use raised spindles bend the arm. That scares me a little, but it is an option.

One problem with bending the arm is it also shortens the effective radius of the arm. This alters the ackerman angle.

[304065]

I can't bend the arm, it's against our race rules.

If you bend the arm, like the 935 (so I'm told) you shorten the arm, which tends to increase the steering ratio. Metallurgical issues with that also.

My car is as low as it will go, and the steering is very difficult at high speeds and high g's. The steering forces are very high. Bump-steer is also pretty significant, particularly in places like the apex of the downhill at Lime Rock. Lots of apexes seem to have a wowie in them, I have noticed, that upsets the car just at the point of max lat.

[Craig 930 RS]

I installed the ERP BS kit back in 1999 - one of the first things I did after buying the 911 was lowering & corner balancing -- and consequently adding the BS kit.

I looked at the fracture closely just now - and IMO I am certain it isn't from overtorquing. Very unlikely.

Your opinion?

[Chuck Moreland]

I'm no metalurgist. But that looks like it was worked back an forth, leading to fatigue.

[jfpound]

Am I seeing that right? It looks like the area that just failed is a rectangle in the center of the bolt? I need a closer shot. It looks like there was a crack on either side of the fracture. Overtorquing causes the bolt to yield and thus reduces it's fatigue life and ultimate strength. That could have been what started the problem. Though I don't like the long bolt bump steer solution either.

[emcon5]

How does the other side look?

Tom

[Craig 930 RS]

Haven't checked the other side - my confidence level in this setup is LOW right now.

Chuck...........WHAT HAVE YOU GOT PLANNED?

[Zeke]

Originally posted by Craig911
Haven't checked the other side - my confidence level in this setup is LOW right now.

Chuck...........WHAT HAVE YOU GOT PLANNED?

Whatever it is, it won't be some long ass bolt with a tie rod end on it. Given the the design of the triangulated front strut brace, I expect something similar as a tie rod.