308QV gearbox filler port thread stripped

Discussion in 'Technical Q&A' started by rjdavatar, Jun 9, 2004.

  1. rjdavatar

    rjdavatar Rookie

    Nov 17, 2003
    Zurich, Switzerland
    In changing the gearbox oil, i removed (for the first time in my ownership) the gearbox filler plug. The plug had clearly been
    tightened by a gorilla who had no access to a torque wrench.

    On removing the plug I ran my finger inside the port, and
    initial 2-3 turns of thread came away as a metal spiral.

    I have tried replacing the plug. It is firm - but I cannot risk torquing to spec. I have taken the car on the road, and there is a small leak from the plug. So something needs to be done to repair, or offset this problem.

    Can anyone provide advice???

    It seems that the plug is not as deep as the filler port; ie, it should be possible to obtain (or make) a new filer plug that is a little longer,
    and so can bite on the remaining thread. Is that possible,
    or does the port thread taper with depth?
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  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    Full Name:
    Steve Magnusson
    The threads are not tapered so if you have some deeper portion of the female thread that is still OK then a longer plug would work. (Since it's a fill plug rather than a drain plug) Another option is to use a non-hardening sealer (e.g. Loctite PST) on the copper washer faces so you don't need as much torque -- i.e., relying on the sealer, rather than axially deforming the annealed copper washer, to form a good seal.
  4. yelcab

    yelcab F1 World Champ

    Nov 29, 2001
    San Carlos, CA
    Full Name:
    Mitchell Le
    Since this is a "filler plug" it is not going to be constantly seeing much oil and pressure. I would suggest an easy fix: goop the plug up (on the side only) with grey or red RTV silicon, install it, and let it sit until dry. Wipe off the ooze on the outside. It will seal, and be reasonably easy to remove next time.

    The proper fix, and much harder, is to take the transmission case to a machine shop, have the drill it out, retap for a helicoil, and install a helicoil. They do make them that big. That is not going to be cheap, or fast.

    Good luck.
  5. atlantaman

    atlantaman Formula 3

    Mar 31, 2002
    Roswell, Georgia
    Full Name:
    next time you have the plug out--go to a parts shop and see if a GM or Ford--ect plug is available that is slightly larger--then drill out hole and retap to new plug size--it is not a hard job to do with the motor in the car--BUT you will need to remove the oil pan so the metal scraps wont be in your tranny.
  6. ferrarifixer

    ferrarifixer F1 Veteran

    Jul 22, 2003
    Full Name:
    Phil Hughes
    This is a common problem. It's not all due to gorilla's either. The combination of aluminum case, copper washer and steel plug all work against each other....ask any boat builder......

    Using a longer bung is the best option. They are out there, but a machine shop is the best bet. It won't cost much, and if you made 6 or so you'd soon get rid of them on here!

    When changing oils, it will pay dividends to use aluminium washers instead of copper. The chemical reaction softens the metals.
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  8. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
    would it be advisable to put a touch of anti-seize on the threads? I did this last time I changed the gear oil, just because it seemed rather difficult to remove, and I know I did not over-tighten previously. I was concerned with galling, like what appears to have happend to rjdavatar.
  9. slewman

    slewman Karting

    May 4, 2004

    Get a filler plug for the differential of a 635csi BMW there is a long (20mm)and short(12mm) plug. It has longer threads and has the same diameter and thread pitch so you you will not have modify anything.
  10. rjdavatar

    rjdavatar Rookie

    Nov 17, 2003
    Zurich, Switzerland
    Thanks for the suggestions....

    I tried using Hylomar universal gasket compound on both sides of the
    copper washer. Nevertheless, there is a slow leak, because I cant apply torque without skipping threads.

    Next approach will be to follow Slewman's suggestion of the longer
    BMW plug.

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