Transmission mount bolts falling out!

Discussion in 'GM Powertrain' started by moogvo, Aug 5, 2012.

  1. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    This is an odd issue that I have never seen before... The two bolts that hold the tail end of the transmission to the cross member keep falling out. I have replaced them 4 times now. Usually, one is gone and the other one is loose. Sometimes they are both gone...

    Heres the thing... I am using M10/1.50 bolts each time I replace them. I use loctite, lock washers and really torque them down. The holes are not stripped. I can get them in there tight but they keep falling out. I have a feeling that the M10x1.50 is not the correct bolt, even though the factory manual says they are.

    Anyone else have this problem? What do ya do about this?! Anyone know the correct bolt size?
  2. aloxdaddy99

    aloxdaddy99 Epic Member 5+ Years 1000 Posts

    That is an odd issue! How does the actual mount look? Is it badly deteriorated? One way to fix them from coming loose would be to use castle nuts and cotter pins. But that is just a remedy for now that doesn't sound like it actually fixes your underlying problem.
  3. Ape

    Ape Member 100 Posts

    Wow, strange indeed!?!? So I take it your tranny mount has threads in it instead of a through hole that a bolt and nut would use?
  4. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    Yes. The tail of the transmission has mounting tabs with threaded holes. The bolt goes up through the crossmember and threads into the tabs on the tranny. The mount is fine and the threads on the tranny are not stripped out. The holes do not go all the way through the mount tabs... Otherwise I would get longer bolts and put nuts on the top. This one has me scratching my head...
  5. Chris Miller

    Chris Miller Rockstar 100 Posts

    You could try tapping the holes to 7/16".
  6. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    I may have to do that. I could also just drill the holes all the way through the mounting tabs and run longer bolts with washers and nuts...
  7. Sierraowner5.3

    Sierraowner5.3 Epic Member 5+ Years 1000 Posts

    you could try tack welding the heads of the bolts. other wise, go to the hardware store and try a few different metric and standard bolts in the holes.

  8. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    I think I will try the bigger bolts route. The bolts are a bit wobbly when they are not tight. Perhaps someone drilled them out and put larger threads in at some point.
  9. Ape

    Ape Member 100 Posts

    Could you try some stage 8 fasteners perhaps? They're designed to use some type of metal potrusion to keep them locked such as you have with headers. But I know guys that have used them in other applications as well.
  10. Mustangflyer

    Mustangflyer New Member

    Try using the required bolts but with safety wire holes in the heads or drill them. We use them in the aviation industry and are very secure. Either safety wire them together or to a tab hole but make sure the safety wire is wired so it's pulling tight rather than opposite. I have the same problem and this is how I cured the problem.

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