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Wheel Spindle Failure - 1978 911?

Greetings . . .

Have any or some of you had a wheel spindle failure ??

We had a right front spindle snap off at the small end taper near the outside wheel bearing during
a race qualifying session at Thunderhill Raceway in Northern California.
I assume the struts and spindles are original to the 1978 911, but they have been modified for
racing.
Some of our friends have said - you are running too wide of a tire - well, we are using Hoosier R7
245/40/17 tires and have for the past 9 years . . . and even though Porsche builds an excellent
quality machine - we may have exceeded the stress limit on the front spindle

I just thought I would ask if someone on this Forum may have had a similar failure and what your
experience was and maybe how you were able to prevent this from happening in the future ??

Thanks in advance for any information you might provide.

Regards,

Photo of failure - -
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Roy T
2002 Porsche Boxster S Cobalt Blue/Blk/Blk
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Previous Porsches: 1958 356 Red Coupe - 1972 914 Blue -1972 911T Coupe Aubergine
Old 10-17-2017, 12:04 PM
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Well that's certainly a bummer. I've heard of spindles breaking before on 911 racecars, but rarely. Your tires aren't THAT wide. I wouldn't think that would be the issue. Our 911 parts are getting old... do you hit the curbs a lot when cornering?
Old 10-17-2017, 03:19 PM
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Never seen it. Wonder if the outer bearing was on properly, too tight or too loose. Did it looked burned like it got too hot
Old 10-17-2017, 03:19 PM
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If you look at the broken surface can you see where the failure originated? You may be able to see subtle "rings" that emanate from a point on the surface of the spindle. Check that location to see if there was a defect on the outer surface of the spindle. I defect such as a nick or scratch could be a site where a crack starts. Maybe over the years something wore or fretted or saw damage during rework. I'm hoping this is the problem otherwise I need to start worrying about this too!

Pete
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Old 10-17-2017, 05:03 PM
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Thanks for the replies - -

Curbs = not at the Thunderhill track, but at our local short tracks my son uses the curbs a lot . . .
Also, we race on both clockwise and CCW tracks - Thunderhill was CCW (mostly left turns) - I
looked very closely at my son's video (several times) and didn't see any back curb hits or
off track when the break occurred . . . However, I did notice a right rocker fiberglass
break near the rear right wheel - I'll look closer at the right side of the car bottom . . .

Bearing = that was the first place I looked for cause of the failure - not burned or out of grease -
or material failure of the bearing . . .

Defect such as a nick or scratch could be a site where a crack starts = I will look closer at this,
maybe take to our Indie who does our engine work and some of his friends -

We are replacing with two new Bilstein RSR struts/spindles from Clint at Rebel - ordered last week.

I am also waiting to hear back from someone I think had a similar failure . . . not many out there . . .

Regards,
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Roy T
2002 Porsche Boxster S Cobalt Blue/Blk/Blk
Crew Chief for Son's 1978 Porsche 911SC Brown 3.8L NASA race car
Previous Porsches: 1958 356 Red Coupe - 1972 914 Blue -1972 911T Coupe Aubergine
Old 10-17-2017, 07:30 PM
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9 years of racing on slicks + 40 years of life? Assuming this is an original spindle, it has just run it's course. Over a long enough period of time all items are wear items.

edit: say even if you didn't have any scoring or anything to suggest it was prone to fail (regular reports of failure given similar circumstances), some pieces aren't created equally...even by the porsche factory. Maybe your spindle falls in the lowest 10%

Last edited by FJ40runr; 10-17-2017 at 08:28 PM..
Old 10-17-2017, 08:24 PM
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I feel for you. It's a total surprise when that happens. I had it happen decades ago to my 1956 Austin Healey 100-4. I kept hearing a scraping noise when I'd make left turns. Started out fairly quiet & got louder. I investigated the suspension and associated parts & couldn't find anything. Going to work one night driving at about 25 mph +/-, the scraping sound all of a sudden got louder, the right front of the car dropped, and I saw the right front wheel take off, jump the curb and climb part way up a tree trunk. The spindle had been failing at the base. At that time a new one cost $40 & labor was something like $20.
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Old 10-17-2017, 08:53 PM
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There's cars with old struts that have been raced a lot longer than 9 years on Hoosiers and the spindles hold up fine. They're a very strong forged steel and don't commonly break like that.

But I don't disagree with the perspective that these cars are only getting older and nothing lasts forever. We're going to see more and more uncommon failures as the years go by. We in this old Porsche community are pretty fortunate that these cars were built to a very high standard of design/durability and many parts are much higher strength than needed for everyday road use.
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Old 10-18-2017, 09:58 AM
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I'm not there to inspect the spindle but my hunch would be classic metal fatigue. Imagine the number of heat cycles that spindle has been through. During the manufacturing process not all of the metallurgical components of the casting will lineup. This leaves a small I.e. microscopic imperfection in the metal.

For those that race older cars, it pays to have highly stressed components X-rayed or magna fluxed, i'm no expert on this but after every wreck I have had I get the primary components of the suspension magnafluxed.

Safety comes from prevention. Prevention comes from inspection. If the spindles were modified in anyway for racing the alignment of the metallurgical components could have changed in compromise the part over time
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Old 10-18-2017, 11:00 AM
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I've seen it once, about ten years ago, at Willow Springs. Also a car running sticky tires with a ton of track miles. It happens, but seemingly rarely.
Old 10-18-2017, 02:16 PM
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Replace front struts

Progress Report:

Wheel bearing spacers pressed onto new Bilstein RSR strut spindles - done
Bilstein damper inserts installed into strut housings and spring pin inserted/hammered into struts - done
Coil over springs placed on struts - done
Struts installed onto lower ball joint post and wedge installed - done
Top of struts inserted into upper monoball camber plate and nut tightened with electric impact tool- done
Bump steer steering drop links (Rebel part) installed and Turbo tie rod attached - done
New brake rotors installed on hubs - done
Wheel bearing races pressed into wheel hubs (new HF hydraulic press added to shop) - done
Brake line mount installed on strut with fresh air brake cooling plates - done
Wheel bearings greased and hubs installed onto spindles - done
Brake calipers installed and fluid lines attached - done
New brake pads installed - done
Bleed brakes with pressure tank and fresh fluid - done
Clean wheels and mount on hubs - done
Lower car and rough measure fender height (car will be corner balanced and aligned at shop at a later time) - done

Everything seems tight and moving correctly - not sure when we will have the car out
for a road test - because race car - maybe in January . . .

Thanks again for the replies to my post . . .
Regards,

PS: Why do my photos turn sideways - how can I correct this??







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Old 11-30-2017, 11:02 AM
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Would coilovers put more pressure on the spindles?
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Old 11-30-2017, 11:53 AM
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Quote:
Originally Posted by 911 Rod View Post
Would coilovers put more pressure on the spindles?
Perhaps . . . but the springs are close to the same pressure from the 24.5 torsion bars we removed.

I am thinking that the failure was caused by a race track curb encounter . . . I found some right side rocker damage from the very low competition rocks we have added for aero.

The coil over springs do seem to provide better car control over rough surfaces - and track curbs.

Regards,
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Old 11-30-2017, 02:08 PM
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Quote:
Originally Posted by 911 Rod View Post
Would coilovers put more pressure on the spindles?
no
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Old 11-30-2017, 03:24 PM
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Shouldn't happen, but it did, spindles are pretty beefy. First guess was the bearing could've been too loose...or too tight? but , since the bearing was okay, (should be able to just push the washer with a flat blade screw driver, but you know that) I am supposing it was a curb-hit, not registered or realized at the time. Fix it and I bet it won't happen again, hopefully.
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Old 11-30-2017, 05:07 PM
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Looks like a fatigue failure, and it occurred at a stress concentration (the transition from cylinder to taper) not unexpected or parts that are so old. Metal can only be cycled so many times before it eventually lets go. Any stress concentration, scratch, etc will accelerate the the failure. Which is why it's important not to gouge up spindles and hubs when replacing the bearing races. I've seen spindles break at the track in a similar way. It was probably cracked for a long time before the crack spread far enough for the remaining material to be insufficient to carry the forces and fail in a tensile overload. A race shop I know that build custom struts often does dye penetrant inspection of used spindles and hubs to look for hidden cracks. You can get a cheap dye penetrant kit from Grainger.
Old 12-01-2017, 07:05 AM
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Hopefully no folks were hurt and the car was not too badly damaged.

I have seen some spindle failures and heard of others during my 30 years of AX, track driving and racing Porsches. I don't know of any specific cause/effect trends. I cannot imagine that hitting berms routinely is good for this kind of part.

I have a lot of experience at Thunderhill, and cannot think of anything about that track creates greater likelihood for this kind of failure.

Back in 2009, my car (1975 911 race car) had a right rear hub failure at Thunderhill when my wife was behind the wheel. Did quite a bit of damage and there was a flash fire.

Just this year a friend had a left front hub fail at Sears Point, AND then a right rear 930 hub failure at Thunderhill. He is a very experienced and skillful driver and has technical acumen that is greater than average.

When the 930 hub failed, there were quite a few experts trackside, including some that have been part of World Championship winning Porsche factory teams (from 935 days through modern times).

I think that many of these parts are getting older and older and the way that we use them is for the most part okay, but statistically these things can happen.

When my right rear hub failed the stub axle was broken as well. I decided on some used replacements from my local dismantler (one of the largest and most experienced in the world). They are 20 minutes from my house and I can often go there and pick parts that are still on cars that I can look at and assess. After I bought the parts, I had them checked for cracks.

I think that those of use that are using these cars for performance driving should continue to inspect things carefully-- or perhaps even more carefully than what we'd do back 15-20 years ago.

I am not yet convinced that we should be timing out these kinds of parts like high-level racing teams.
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Last edited by Mahler9th; 01-31-2018 at 04:38 PM..
Old 12-01-2017, 07:49 AM
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Progress Report - New Struts . . . another issue . . .

Well,
The new RSR Struts are in with new wheel bearings and Rebel Bump Steer kit . . .

However, it appears the old struts were modified more than just raised spindles because
with the new struts/spindles we can not get to 3.5 camber - only about 1.5 - 2 - not
good enough for racing on 245 Hoosier A/R 7s . . .

We have decided to make further improvements in the suspension by using Rebel's 935
front suspension replacement kit that will allow much more camber - and easier adjustment.
I ordered today from Clint and plan to be track ready in 2-3 weeks.

Wishing everyone a Happy New Year - cheers!

Regards,
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Old 01-05-2018, 12:50 PM
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I have Clint's second steering arm and Heim joint on my struts too. I raised the spindle 26mm and took 1 of camber out at the strut. The de-cambering won't allow coilovers AND 205 tires under stock narrow body fenders so I still have T-bars.
Old 01-05-2018, 03:56 PM
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My question is (if I may) does your Heim joint thread as far up the turbo tie-rods as mine? Clint said the arm and bumpstop set up looks correct but I forgot to ask about the treats.
Old 01-05-2018, 04:08 PM
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