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Gearbox leak

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  • Gearbox leak

    My Dogleg CR has a leak but I just can't find it. I replaced the shift rod seal, but it's not coming out of there, it's seems to come from the top of the gear box, only when I race, not stationnary.
    Anyone experienced that.
    Maybe I put too much oil. I keep it flush to the fill hole.


  • #2
    You're probably getting it out of the breather hole at the top of the tranny. I know some racers have made catch tanks for the breather hole. Don't know the details about how. I think club racing mandates that you not allow any fluid on the track. But I'm not a racer so I can't speak with authority on that. HTH



    • #3
      I had a similar problem with the trans on my Touring Car (which is essentially a magnesium case, dog clutch version of the CR box).
      The leak appeared to come from above the trans, when driven on track.
      I had a vent line and catch bottle on it, so it was not the vent.

      There are some plugs / sendors (2 or 3) on the sides of that trans in the side that take crush washers.
      I think they may be for a speedo sender (Not used on the M3 app), and possibly back up lights? Mine were all over torqued or completely missing.
      In any case I replaced all crush washers (one is a very wierd size, like 14MM, hard to find locally).
      My leak persisted,,, still only at speed, only when driven hard.

      This winter I yanked the trans and pulled the front cover off.
      I replaced the front seal and the gasket between the front cover and the front section of the housing. I have not driven the car yet, but judging by the looks of the parts when I disassembled, I am 99% sure thats where my leak was coming from.
      At some point someone had reassembled my trans with no paper gasket, just RTV between the front cover and the front section.

      FWIW,,, my friend Geoff was having a very similar issue with his CR box and this winter, after I told him about mine, he just did the exact same procedure I did (his still did have a paper gasket upon dissasembly, but it was saturated badly).
      Neither of us have driven the cars yet after the fix, so its unknown if that fixed it, but I gotta think this time I got it.

      I'd take the easy route and check in this order:
      1) Vent on top of trans
      2) Crush washers in side gallerys (I think 2 -3 total, up high, on sides)
      3) Front gasket and input shaft seal

      jimmy p.
      87 E30 M3 Prodrive British Touring Car
      88 E30 M3 Zinnoberot - Street
      88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
      92 E30 M Technic Cabrio - S14 POWERED!
      98 318Ti M44, Base - Morea Green
      04 Ford F350 - V10


      • #4
        Would it make sense to apply gentle air pressure by the vent hole to hear where the leak is??? Just an idea.