Crossmember does not fit

Discussion in 'High Tech Retrofits' started by indyzmike, Apr 18, 2014.

  1. indyzmike

    indyzmike Veteran Member

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    I have a G-Force F2-700 crossmember for a 700r4 that is too narrow to fit the holes in my 1980 Z28 subframe. The frame holes measure 31-9/16ths inches. The crossmember holes measure 31 inches. Is my frame warped or is the crossmember too short? G-Force says it is the correct crossmember.
     
  2. toddoky

    toddoky Veteran Member

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    That crossmember is only designed to fit the 1970-74 2-gen as a bolt-in component. The crossmember mounting holes for those cars are located in the formed pockets on top of the rails towards the rear of the subframe. The 1975-81 F-body crossmembers were installed forward of the pockets and the mounting holes were moved accordingly towards the front of the vehicle and at a different width from the early pattern.

    You may still be able to use that crossmember, but you'll have to mount it in the formed pockets (the pockets are still there, just the holes are missing) and drill new mounting holes in the subframe. Do a dry-run install and check the engine inclination/U-joint angles that you get from that exercise before drilling the frame so you can return it if it doesn't work for you.
     
  3. 77nomad

    77nomad Veteran Member

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    Won't that move the location of the mount in relation to the trans? If the engine trans didn't move rearward toward the "pockets" and the crossmember did, wouldn't the mount on the transmission be off the exact distant the crossmember was moved? Being that you are only off a little over 1/4" per side can you open the holes up? If you have access to a welder you can open the holes and fill in the remainder of the old hole. Even with oblong I'd run it. Maybe add a couple hardened washers to help support the bolt head. Maybe I'm thinking about it all wrong but moving it back seems to be a no win situation.
     
  4. toddoky

    toddoky Veteran Member

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    He wouldn't be moving it back relative to its intended installed position; the stock mounting location used on 1970-74 cars and where the crossemember itself was designed to be attached is rearward of the stock holes he has in his subframe.The crossmember he has was designed and intended for use on a 1970-74 car, which means to have it attach in the formed pockets on top of the frame rails, near the rear of the subframe; the position of the mounting pad would then be cantilevered forward from the subframe attachment holes to land in the correct location for the 700R4 mount. If it was designed to install a 700R4 into a 75-81 car, which it's not, then its build geometry would be configured to attached to the more forward located holes in the late subframes and pick up the center mount that that would be slightly rear of the subframe holes. The crossmember needs to be attached to the subframe in the fore/aft position it was intended to be by design for the geometry to work out.
     
    Last edited: Apr 19, 2014
  5. 77nomad

    77nomad Veteran Member

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    OK. My thinking was a little skewed by the short front end on early cars. For some reason I was thinking the motor mounts were farther back too. But after actually using my brain I understand the extra distance was in the core support area.
     
  6. TheMeat

    TheMeat Veteran Member

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    Looks as though it is advertised as only fitting the 70-74 cars...? I have had two different G-Force crossmembers for two different transmissions and both have fit perfect. However, my car is a 73.


    [​IMG]
     
  7. mrvedit

    mrvedit Veteran Member

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    I have the G-Force #770318 in my '81 with a 4l60E trans. As Toddoky explained, it has several inches of cantilever.
    That is the part you want. It is very sturdy and I am very pleased with it.
    Note that it only works with trans mounts that have two bolts into the crossmember. IIRC asking for a trans mount for a '70 Camaro 396 works perfectly and costs only $8 at a local store. Most Poly mounts fit too, but since they tend not to be as tall as OEM, you may need a 1/4" spacer under a Poly mount. The G-Force also has mounting slots giving you about 1" of possible positioning.
    I originally used it with a 0" offset, but with the 1" slots, it should work with 1"-back offset too.
    I most recently changed to the Hooker mounts (and headers) which are about 1-3/8" back. For this I had to move the G-Force back, reusing one stock hole and having to drill only one new hole on each side.
     
    Last edited: Apr 20, 2014
  8. toddoky

    toddoky Veteran Member

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    Most people either have a 1970-74 car or a 75-81 and aren't aware of the different crossembers and mounting locations between the two versions of the cars. Once GM dropped the TH400 option, the mounting holes were moved forward on the frame and a the use of a new-design crossmember was implemented. However, the formed pockets in the subframe where the previous crossmember was attached remained, so you can (in most cases) install a 70-74 crossmember in those pockets by drilling the four needed attachment holes and relocating the crossmember there.
     
  9. 77nomad

    77nomad Veteran Member

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    Actually 8 holes. You need to drill the frame to gain access to them. Larger diameter as well.
     
  10. toddoky

    toddoky Veteran Member

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    Technically speaking yes, four attachment holes and four access holes cut beneath them with a hole saw...I was giving the shorthand answer to the question.
     

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