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Difference between K20 and K30 465/205 crossmembers?

Discussion in 'The Garage' started by Russell, May 2, 2006.

  1. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Hey guys!

    Is there a difference between a K20 and a K30 SM465 / NP205 combo crossmember? I've got a K30 one on my K20, and I've got t-case to cab clearance issues (was a 2wd low hump cab BTW)
     
  2. yellowK20

    yellowK20 Well Lubricated Premium Member GMOTM Winner

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    it's the 2x4 cab that's the issue I've swapped cabs you need to either use a 4x4 floor or ru a 2inch body lift
     
  3. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Would I be endangering anything if I dropped the crossmember 2" instead of lifting the cab 2"?
     
  4. tarussell

    tarussell 1/2 ton status

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    K-30 cross members are flat due to the deeper frame rail center section on the one-ton frames. If you are using a K-30 x-member on a 1/2 or 3/4 ton frame than you will be making the transfercase mount way out of wack by shoving it upward.

    Tom
     
  5. yellowK20

    yellowK20 Well Lubricated Premium Member GMOTM Winner

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    you might be dropping it to far Do you have your stock k20 crossmember to compare???
     
  6. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Unfortunately no, and I don't know where I can find a K10 or K20 to take a look...

    I found that if I drop the t-case about 1", the rear u-joint angle looks alright, and I have about an inch clearance for both my exhaust and my cab. I'll probably build myself a 1" aluminum spacer for each side, and some 8th grade software, and call it good.
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    At one time I thought I had seen it stated that there was no difference in the 1 ton vs. 1/2-3/4 ton crossmembers, but that the 1 ton was bolted inside the framerails and the 1/2-3/4's were underneath, and that was how the frame difference was accounted for.

    Is that incorrect?

    I know the early 80's x-member was flat, 1/2 ton etc., but the later stuff (approx. '85-up?) isn't, which changed with the "short" adapters.
     
  8. tarussell

    tarussell 1/2 ton status

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    On the 1984 on down X-members they are definetely different on the K-30's but I can't remember what they did on the 1985 and newer ones . The frame is still deeper on the 30 series trucks - maybe GM did some cool engineering and made it possible to use the same X-member and just chjange the mounting point on the 1985 on up stuff ?

    Tom
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    Well, I *think* the change across the board for x-members was in '85. I only know the 465/205, that adapter changed when they went 32 spline on both, so the crossmember is "taller". (those are the single or doublehump crossmembers as I call them)

    My original crossmember was out of an early 80's truck (still '81+) and it was flat. People that have '84 trucks can state whether the crossmembers were still flat then.

    I don't know the frame height difference one ton vs 1/2, but since GM did things like changing the adapter length to lessen the varieties of driveshafts, it would make sense to do similar with the frames if possible.
     
  10. tarussell

    tarussell 1/2 ton status

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    Yeah , the flat X-member was last used in 1984 when the change in adapters was made for 85 . The only parts of this I know for sure is that the 1984 on down 30 series X-members are different than the 1/2 & 3/4 ton frames and the frames on the 30 series trucks was the same depth before and after 1985. I dunno what they did between X-memebers after that - the short adapter X-memebers are still a mystery to me ......

    Tom
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    So the crossmembers for one tons (at least pre-85) would be "shallower" than those for the 1/2 tons, right?

    Anyone got pics of these 1 ton crossmembers? I'm curious to see how exactly GM did it. Just interested in these things. :)
     
  12. tarussell

    tarussell 1/2 ton status

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    I have both styles of X-members but I am useless as hell on the computer and do not know how to post up pic's - sorry ......

    The flat style K-30 x-memebers are flatter than the other ones - they do not flare upwards at the frame attacthment points like the 1/2 ton ones do . The adapter mount is in the same place/position but the X-member is flatter to meet the deeper K-30 frames where as the 1/2 ton stuff has a shorter frame center section and the x-memeber needs to be flared up at the ends to meet the frame rail.

    I hope I have not confused the stew out of Ya" ......
    Pic's would be best to easily see the differences.

    Tom
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    I understand what you are saying...it makes sense, to keep the drivetrain in the same relationship with the body, moving the x-member up (by flattening it) would work fine.

    Not a whole lot of one tons I've parted out, although my friend DOES have an '83 C30, which would have the crossmember you describe I guess!
     
  14. tarussell

    tarussell 1/2 ton status

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    YOU GOT IT ! Right on the money ......

    Tom
     
  15. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Well, sounds like I need a half ton crossmember. Mine is totally flat, and makes the t-case / tranny sit up a bit tall compared to where a normal SM465 / 205 should...
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    Can you shoot a picture of it? There are plenty of photos of the 1/2 ton one floating around, I think one of my t-case shots shows it pretty clearly.

    From my experience the crossmembers changed in the 70's sometime, as my friend offered one to me from a '75 or so, and it wouldn't fit on my '81 frame...the width was different.

    I don't recall the "height" of it though, if different.
     
  17. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Sure, I'll snag a picture tonight
     
  18. colbystephens

    colbystephens 1 ton status GMOTM Winner

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    :haha:
     
  19. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Quiet you! Old stacked AOL CDs make excellent crossmember drop spacers!!
     
  20. colbystephens

    colbystephens 1 ton status GMOTM Winner

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    hey, i can appreciate someone making something useful out of something seemingly so useless as AOL! :D
     

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