2nd Gen R56 Cooper S Trailing Arm stripped bolt hole

Discussion in '2nd Generation: 2007+ R55 through R61' started by grodenglaive, Jul 19, 2011.

  1. grodenglaive

    grodenglaive New Member

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    This isn't good. When reinstalling the left rear shock, I stripped the lower bolt hole where it attaches to the rear trailing arm. :(
    The big M14 bolt screws directly into the aluminum trailing arm, there is no end nut. Pretty dumb design.
    I think I can replace the bolt with a longer one that passes all the way through the arm so I can put a nut on the end. Way cheaper and easier than replacing the trailing arm. Does that sound feasible?
     
  2. TT_Zop

    TT_Zop Club Coordinator

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    Did the same thing on my R53. Longer bolt and nut works with no long term issues. Used blue loc-tite on it also.
    Actually got new bolts from dealer and used nuts on end now that I think about it.
     
  3. Nathan

    Nathan Founder

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    The 1st gens did use a nut and bolt there. When MINI when to the Al trailing arms on the 2nd gen and the GP the bolt became a self threading one for both ease of initial assembly and it's one less part to source and keep in inventory. While that seems silly on the face of things when you consider that is spread of 1/2 million cars or so it starts to make sense.
     
  4. Crashton

    Crashton Club Coordinator

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    Lots of things were changed for the sake of easier assembly & add more profit in the companies pocket. Seems to me they must now stock trailing arms instead of bolts & nuts. Now that is progress.

    Back on topic....

    Using a longer bolt & nut seems like the correct fix for this.
     
  5. grodenglaive

    grodenglaive New Member

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    thanks for the confirmation:)
    I'm off to the hardware store...
     
  6. Crashton

    Crashton Club Coordinator

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  7. Metalman

    Metalman Well-Known Member
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    Be careful what you get at the local hardware store. Suspension bolts on vehicles are rated at a much higher tensile strength (for obvious reasons) than whats available as a generic bolt for say putting a hinge on a gate door. This is an area where you don't want a failure.
     
  8. Crashton

    Crashton Club Coordinator

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    ^ + 1 & how!

    You may be able to check the grade by looking at the markings on the original stripped bolt.
     
  9. grodenglaive

    grodenglaive New Member

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    Good points! They had grade 8.8 in stock, which is hopefully good enough. I also ordered the stronger 10.9 just in case and will swap it out when it arrives.
     
  10. grodenglaive

    grodenglaive New Member

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    so here's the result.
    old bolt hole:
    [​IMG]

    modified arm:
    [​IMG]
    It took a bit of grinding to make the trailing arm flush for the nut end - it's hard to tell in the "before" picture, but the surface is angled, not flat.

    old bolt, new bolt and the threads that came out of the aluminum trailing arm:
    [​IMG]
    It turns out, the original bolt is a 10.9 hardness, so it's a good thing I checked (thanks crashton). That's only an 8.8 in the picture, but I have replaced it.

    end result:
    [​IMG]

    Can't say I'd recommend doing it this way. The trailing arm is not going to be as strong after the grinding, though not that much material was removed. In retrospect, perhaps a heli-coil insert would have been a better way to go, but I would have needed to bring the arm to a garage to have it done. Also I didn't really trust that it wouldn't pull out again with a heli-coil.
     
  11. Metalman

    Metalman Well-Known Member
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    #11 Metalman, Jul 30, 2011
    Last edited: Jul 30, 2011
    Just wondering if it was corrosion that got in between the aluminum and steel threads (I think so)? Then when originally removing (dry) the bolt and the aluminum threads were stripped. Perhaps spraying with a penetrant lubricant, sitting over night to let it traverse all the threads, would have prevented this? Then upon re-assembly, coat the threads with anti-seize?
     
  12. minimark

    minimark Well-Known Member

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    Simple and professional way to prevent this is to apply anti seize on suspension fasteners to begin with and then torque the fasteners to the proper specs. Anti seize can be purchased at almost any of your local auto parts stores. 2cents
     
  13. Crashton

    Crashton Club Coordinator

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    grodenglaive -

    I have a couple of thoughts. Since that is a steel bolt going through aluminium I'd pull it out & coat it with anti-seize where it goes though the control arm & shock. The reason I'd do this is to prevent any corrosion you may get from the contact of aluminum & steel. While it is out I would also use threadlocker (blue) on the bolt & nut. Keep an eye on it, but my best guess is that you will be alright with your repair.

    Good job.... :Thumbsup:
     
  14. Metalman

    Metalman Well-Known Member
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    Yeah...+2 on the blue locktite...:D
     
  15. Metalman

    Metalman Well-Known Member
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    Lynn just suggested to me that you don't want to contaminate the two materials for obvious reasons. Yep the anti-seize will nullify the loctite if you contaminate the two. Sooooo, don't mix the two. Also, try and match the thread pitch to the original which looks to be a fine thread versus the coarse thread on the replacement bolt.
     
  16. Crashton

    Crashton Club Coordinator

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    I'd keep the anti-seize on the shoulder of the bolt not the treads. The loctite on the treads will keep the moisture out & keep the threads from rusting. I agree cross pollinating chemicals can be bad ju-ju.... :wink:
     
  17. Onasled Racing

    Onasled Racing New Member

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    Forget loctite and just use a nylock nut.
     
  18. Crashton

    Crashton Club Coordinator

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    He has a nylock. It's been my experience that loctite keeps mosture out & thereby keeps corrosion at bay. Probably more important for a street driven car than a race car. I'd use both, just my .02.
     
  19. Onasled Racing

    Onasled Racing New Member

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    Antiseize, loctight, nylock? Really? Just antiseize it with the nylock. Forget loctite.
     
  20. Metalman

    Metalman Well-Known Member
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    It's not going to be that big of an issue for you in the future now that you made the change. You've eliminated the ability of the corrosion between the OEM aluminum threads and OEM bolt (since they don't exist anymore and don't intimately make contact with each other), so no more stripped aluminum threads. Your only issue now is to make sure you don't have a loose connection..... You'll always be able to get this fastener off in the future (even if you need to cut it off). The point is you didn't need to buy a new ($xpensive) trailing arm. And you did it yourself, versus a trip to the dealer.....:D

    When you do the other side...... Spray the open side with liberal amounts of penetrating oil and let it sit so it can soak into the threads before you go at it with the wrench.....:D
     

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