Almost lost a wheel - lug nut question

[jeffgrant]

So, I feel like an idiot, but only partially. Now I'm more confused than anything, and need some advice/thoughts.


I was on my way out to the vintage races at Mission over the weekend, and the rear end in my 930 developed a bit of a vibration that got progressively worse as I went on.

The last time I'd driven it was a few days earlier at a DE, so I figured that I'd blown a chord in the tire, but after pulling off and checking it, that didn't seem to be the case.

I proceded, driving painfully slow (lots of gesticulating from the Chevettes passing me like crazy).

It got so bad that I eventually pulled off and had it towed, thinking for sure that it was a rear wheel bearing that let loose (one was replaced about 20k ago, figured the other one had given up the ghost).

Long story short, had it flat-bedded to Weissach, and low and behold, the lug nuts on my rear-left wheel were loose.

Once off the ground, 4 of the 5 nuts were loose enough to undo with my fingers.

Very strange.

Even scarrier, is that ALL the lug nuts, on all 4 wheels, were coming loose.

Now, the torque was tested at 94 ft/lbs 3 times before the DE, (the night before when I checked them, and twice the morning of the DE at the tech inspection) and the car was locked in my garage until the trip out to Mission, 4 days later.

Anyone have any idea what could cause something like this? Will over-torquing, followed by lots of heat, and then cooling, cause this?

I'm stumped.

The only thing that was suggested was that maybe someone had tried to steal the wheels and hadn't gotten as far as they wanted before they were interrupted.

But that seems highly unlikely.


Thoughts?

[Wil Ferch]

quote..." Will over-torquing, followed by lots of heat, and then cooling, cause this?..."

I think it will....

I believe the drill is to torque cold to 95 ft-lbs spec. They will tend to loosen with heat, then you torque up to spec again...then when it cools down later.... it'll be loose.

Perhaps others can offer advice if using steel lug nuts for DE's is better for this aspect ?? I like them because they're open-top and you can see the 1-2 threads sticking out when tight.

- Wil

[jeffgrant]

I've always been told to NEVER torque nuts/etc when warm/hot. The 94 should (from what I've been told) be done cold, and left alone.

Hmmm... this should be interesting...

[ZOA NOM]

Dude, somebody is trying to take you out.
It's a thief or a killer - take your pick.

Did you pi$$ somebody off lately?

[Grady Clay]

Jeff,

What is the configuration of your wheel attachment? Is it stock 930 Turbo? Is it ’82 911SC? What wheels? Spacers? Wheel studs?

I have never seen a 911 or 930 loosen the lug nuts with all the normal Porsche parts.

Best,
Grady.

[pwd72s]

Originally posted by SoCal911SC
I agree. If you torqued them to 95 lbs, didn't reloosen them, and within a couple of days they were ALL loose enough to remove by hand - then someone loosened them.

95 lbs is spec and is a lot of torque. They don't just come loose from 95 lbs.

+1 But you'd better check the accuracy of the torque wrench used.

[rnln]

I am not sure if it's related but a friend of mine had the same problem, on street driving, over times. It was because the lug/nut patern wasn't correct. Well, the patern was correct but the wheels were cheap wheel. The holes were off a little bit.

[Wil Ferch]

I have "come in" from a hot 'n heavy DE run and the 95 ft-lb torqued nuts ( aluminum, torqued cold before-hand) were "loose" when the car was hot. Not as loose as here...but were numerically "under 95 ft-lbs.

Then started the dilemma...do I tighten them ( hot ) or not?

As posted here, the main advice was "no"...since they'd be over-torqued when cooled down. Cycling this way can't be good....but what do you do on subsequent DE runs ???

I wonder if the open steel lug nuts behave the same way?

Wil

[dentist90]

If you have worked (raced) the car previously and this hasn't happened I believe EVIL is afoot. I mean really, ALL FOUR wheels only finger tight? Seems like some envious lunatic would like to see a cool Porsche go off-roading. I hope not, but my cynical side rarely lets me down.

[dad911]

Will, do not torque them hot. I did this as a rookie (noticed they were 'loose' after a run) and snapped studs.

[Jeff Alton]

Grady, Jeff's car is DP turbo and has the BBS wheels (wide) that came on in. Has the regular factory 930 geometry, brakes and hubs. He can provide more detail when he logs back on.

Jeff, sorry for screwing with your lug nuts!! Just kidding!

That is pretty strange for them to be "finger tight". What was Stuart's thoughts on the situation? Has anyone touched the car since the DE on monday?

Glad you are okay, this could have turned out much worse.

Cheers

[dentist90]

WeissAss Question: How much does Weissach charge to tighten lug nuts?

[jeffgrant]

Yeah, as Jeff says, there's nothing different about my wheel/stud setup, except that I've got wider than normal rear wheels. That being said, there are no adapters, etc., and it's the normal 5-stud 930 setup.

The only thing is that nobody COULD have messed with the car, unless my wife is trying to kill me or something, as the car was in my locked (padlock) garage during that time, and she's the only other person with access to a key.

I literally parked the car in the garage after the DE, and didn't touch it until the trip out to Mission 5 days later. The way our back alley is set up, I have 2 locked garages (padlocks), and my daily driver is parked in front of the garage with the car in it, so I for sure would have noticed evidence of someone breaking into it.

Also, there were 3 different torque wrenches used, and all showed 94 ft/lbs.


I just don't know what to think.


Anyway, Weissach charged me all of $0.00 today to look at the car, take the wheels off, check for thread damage on the wheels, studs, etc., and put them back on, and tighten them.

Considering that they're full-on busy right now, and it'd normally be a week or more to get into the shop, I thought that was very nice of them.

Marty even let me look over his shoulder while he was doing the work.

[Bullet Bob]

I don't know about anyone else, but after I type this I am heading out to check my lug nuts :-)

Bob

[jeffgrant]

Yeah... my torque wrench is sitting in the car as we speak... probably a permanent fixture for at least a few months, I would think.

[Rob 930]

Jeff,

I've been involved in the analysis of torque loss on wheels and other bits of machinery over the years, so I thought I'd give you my perspective. First, the temperature at which you torque the wheels should not be a significant factor. The temperature differential hot versus cold should not be enough to cause expansion or contraction to the degree that it threatens the integrity of the connection. If loosening was exacerbated by temperature change, then something else was seriously wrong with the connection.

The most common reason for wheel loosening, of course, is inadequate torque. But it sounds like you believe they were tight. Overtorquing can break wheel studs and cause damage to the threaded connection, but it rarely causes a delayed "progressive loosening" of the type you describe -- it usually manifests as an immediate failure of some sort. As such, I doubt that overtorquing was related to this problem. There are other factors that can cause loss of torque, though, that go beyond just the simple act of leaving the wheels loose.

Did you use the same wheels, with the same spacers, and lug nuts as always? Are they steel lug nuts or aluminum? Factory lug nuts? If not factory nuts, do they bear on the wheel with a conical/radiused end like the factory nuts, or do they have an extended "snout" that protrudes into the wheel and has a flat shoulder that bears on the wheel? Certain aftermarket aluminum wheels (especially for domestic cars) often have a thicker section at the bolt circle, which is stiffer than the centers of the wheels they replace (this is especially true when compared with steel wheels). This necessitates a higher torque spec. I realize your 930 never came with steel wheels, but I don't know how thick the bolt flange is on the BBS wheels you were using, and whether or not the 94 ft-lb spec holds true. I suspect it does, or someone would probably have mentioned it by now. The higher the stiffness of that center section, the higher the torque required at that connection, and the less forgiving the wheel will be of torque loss, should one occur.

Is there any chance that something deformed after you torqued your wheels? I've seen clamped components at the wheel progressively deform on the road (never a Porsche, though), causing the original torque to be lost over a period of time. On your car, I can't quite imagine what that could be, though. Just thought you should look around and be sure nothing is "squishing" behind your wheel when you torque it.

The fact that all four wheels were loose is quite revealing. I have to agree with the consensus that the wheels were left loose, or were loosened somehow. It's just very unlikely to have four "failures" simultaneously!

One word of caution: I would consider replacing the wheel studs on the wheel that came very loose. Once torque is lost and the wheel starts to wobble, it puts a cyclic bending load on the studs (which they're not designed to endure) that causes them to fatigue. This is the most common mode of failure in a wheel-off accident -- quite often the nuts don't work their way all the way off the stud -- the wheel wobbles, fatigues the studs, and the studs fracture. It causes progressive damage to the studs that would be hard to see without magnetic particle or dye penetrant testing. Wheels can be damaged this way too. I have heard of wheel coming off after close calls like yours, where studs were not replaced, and they failed sometime later after the wheel was re-torqued.

I bet you'll be checking and checking torque from now on, which is a good thing. Please post again if you find they tend to loosen.

Rob

[jeffgrant]

Rob-

THanks for the insight.

As to the wheels, I've done 7 DE's, a few AutoCrosses, and put almost 18,000 miles on these wheels over the last 2 years, with no problems of them coming loose, etc.

This was the first time this has happened.

I am now keeping a very close eye on my torque, and am going to be replacing the wheel studs.


The ONLY thing (remote as hell) that I can think that would potentially have an effect on this is that I've recently had my wheels refinished, and am wondering if something changed with respect to how the lug nuts meet with the wheel. This was the first hard driving that I've done since the wheels were refinished, and is the ONLY thing I can remotely think of that might be the cause.

[Grady Clay]

Jeff G,

What I was angling for was: Were the wheel studs replaced with longer ones? If the replacement studs are not installed with a hydraulic press, the lug nut 96 ft-lb torque won’t seat them. Use will then cause the studs to pull in slightly and result in loose nuts.

Are these 3-piece BBS? Do the centers have the steel ball inserts for the Porsche lug nuts? Is the wheel centering feature functioning (Is the centering feature on the rear hub in tight contact with the center of the wheel?) Am I correct – you don’t have any spacers; the rear wheel is on the rotor?

No chance that the lug nuts are bottoming on the unthreaded portion of the wheel stud?

Are these Factory steel lug nuts? There is a mark on the OE Porsche nuts.

ALL the suspension, brake, hubs, bearings, trailing arms, torsion tube, etc. are Original Porsche 930 Turbo? What year?

I find it hard to believe this was vandalism or worse. Careful looking will turn up the cause. Is there any chance the wheels were off (bleed brakes, swap tires, etc. and didn't get torqued?

Best,
Grady

[jeffgrant]

Grady-

From what I can tell, the current wheel studs are 100% original.

I'm not sure about the steel ball inserts, but the wheel is centering properly. And no, there are no spacers... the wheels have the proper offset so that the wheel is directly on the rotor.

I've checked the threads, and there appear to be no bottoming on the unthreaded portion... I can't SEE any unthreaded areas on the studs, even with the wheels off.

Not sure if they are the factory steel lug nuts... they feel too light to me to be steel.

All suspension is from an '82 930.


As I just mentioned, I just realized that this was the first hard drive (ie, lots of heat, etc) I've put on these wheels since I had them refinished. (They were taken apart, polished, re-painted, and then re-assembled with new gaskets).

My theory is this:

1) Went nuts at DE, throwing lots of heat into the tires and wheels.

2) Wheels expanded with heat, etc., and were still warm/hot on drive home from track. No problems with lug nuts, as wheels hand't cooled off enough.

3) Car was parked in garage and finished cooling off.

4) During cool-off, something (paint? pollish?) became separated from the wheel, and was between the wheel and the lug nuts.

5) When car was next driven, friction was reduced due to the paint(?) separation, and as a result ALL the lug nuts on the car started coming loose.


This is my current crack-pot, tinfoil-hat theory, and is being looked into tomorrow when the car's at the shop (fuel pump replacement, etc).

To me, nothing else makes sense.

[randywebb]

Who did your wheels? AR paints the concavity around the lug painted (see your #4 above), while HW masks it off, leaving it upainted.

see if any paint is stuck to the convex part of the nut...