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328 CV joint bolt

Discussion in '308/328' started by jha328, Nov 27, 2016.

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  1. jha328

    jha328 Rookie

    May 26, 2013
    18
    Australia
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    John
    #1 jha328, Nov 27, 2016
    Last edited by a moderator: Sep 7, 2017
    A few weeks ago I was pushing the car backwards in the garage. It would stop with a clunk and then I'd it push forwards with the same result and then backwards again and it was fine. Today I go to reverse the car out of the garage and hear several big bangs and then it's ok. Get out and walk into the garage and find the head of a bolt (internal hex) lying on the garage floor. It turns out that one of the bolts holding the outer CV joint has snapped the head off. My question is, how can this happen? Was it over torqued at some time? It's a clean break with no sign of corrosion!
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  2. Pero

    Pero Formula Junior
    Silver Subscribed

    Apr 22, 2011
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    Peter R
    #2 Pero, Nov 27, 2016
    That is very strange. Bolts, if correct ones, are very strong and super hardened. Surprised that the bolt itself is bent, and not snapped? Any damage on the car from the bent bolt?
    Peter
     
  3. bertrand328

    bertrand328 Formula 3

    Jun 1, 2015
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    Bertrand
    #3 bertrand328, Nov 27, 2016
    Who serviced your car ?!
     
  4. jha328

    jha328 Rookie

    May 26, 2013
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    Australia
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    John
    #4 jha328, Nov 27, 2016
    The bolt which broke has 3-12.9 RC stamped on it. I assume that it is an original. The ends of the bolts appear to be approx. 25mm away from the flange nuts and studs and don't appear to have much damage done to them. There doesn't appear to be anything else that the end of the CV bolt could have hit. The bent bolt actually has a split on the outer bend.
    What I can't understand either is why did the bolt head only fall off in the garage and not on the road somewhere.
    The CVs and drive shafts have not been touched since I've owned the car.
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    Steve Magnusson
    #5 Steve Magnusson, Nov 27, 2016
    Last edited: Nov 27, 2016
    The fractured surface indicates that you had a crack starting at the root radius of the head that propagated for a while (the smooth crescent moon area of the break on the left side of your photo) and then the rest failed suddenly (the rough area of the break). The location of the bend indicates the head came off first, then the remainder moved towards the nut side until it hit something while rotating. One problem with super strong bolts is that the extra strength comes with a penalty in toughness. I'd also add that the root radius under the head doesn't look very generous for a grade 12.9 bolt. F typically has a note in the service documentation to always replace these bolts and not reuse, but few do. If the initial damage was from over-torquing, it probably happened during the removal, not the installation (or reinstallation).
     
  6. derekw

    derekw Formula 3

    Sep 7, 2010
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    London, UK
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    Derek W
    #6 derekw, Nov 27, 2016
    The fatigue area (smooth crescent Steve mentions) suggests the tensile load was cycling which shouldn't happen if the bolt is tight enough. It would be interesting to know how much the others are torqued to. Like rod bolts, they are probably torqued to give a pre-load tension above the cyclic tension from the driving.
     
  7. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,962
    Isle of man- uk
    #7 mike32, Nov 27, 2016
    The bolt has been failing for a while, hence the smooth outer diameter and the rougher inside where it finally failed. The 12.9 stamped on it identifies it as an high tensile off the shelf allen bolt. A normal bolt has 8.8 stamped on it. But a new set of bolts and inspect the hole bores for the correct diameter, be sure you check they have not worn oval. If the holes are not damaged or oval then change out all the bolts, check to see if they should have spring washers althrough your pic looks like the nut is a self lock
     
  8. ogrilp400

    ogrilp400 Rookie

    Mar 31, 2006
    23
    #8 ogrilp400, Nov 27, 2016
    I'm interested in the darkish small blob with lines radiating out from it at about 4.30. I had a crank pin on a Vincent HRD motorcycle fail many years ago and it stemmed from the flywheels flexing and small hard spot in the metal, similarly shaped as this one.
     

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