Installing GMT900 rear Cab mounts in a GMT400

Discussion in 'Stock Suspension + Bolt On Kits' started by Aloicious, Oct 13, 2011.

  1. Aloicious

    Aloicious Hired Goon

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    yeah I'm not sure either...I had a diagram with all the measurements somewhere, I'm not sure where it went, I'll have to look around for it.
     
  2. tj98gmc

    tj98gmc I'm Awesome

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    i am planning on doing this,,, but my question is,,, are the mounts from the stock 400's and the 900's that we are putting in the same heights?,, like is it going to lower or raise my cab at all?,, just wondering
     
  3. Horns

    Horns Tiff's Wedding Crasher

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    Yes, they are the same height. Your cab will be in the exact same position as it came off of the line. A lot of people actually do this upgrade when their rear cab mounts wear out and make the cab sag a little bit.
     
  4. kyotey1693

    kyotey1693 Newbie

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    Did anyone find out if the mounts measure the same for a regular cab?
     
  5. Aloicious

    Aloicious Hired Goon

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    okay, I found the measurements, sorry about the crude drawings, but this is a side view:
    [​IMG]

    and here's the "top" view from the above diagram on the left, on the right is its "bottom" view from the diagram above:
    [​IMG]

    hope that makes sense
     
  6. kyotey1693

    kyotey1693 Newbie

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    Cool! I havent measured my truck yet but I looked at LMC's site and it lists the same part # for the ec and rc. So if my logic is right the gmt900 mounts should work right?

    Heres the link. Compare parts 14-17 to 23-26 inside the little box.

    http://www.lmctruck.com/icatalog/cd/full.aspx?Page=23
     
  7. Aloicious

    Aloicious Hired Goon

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    it could fit, I know the RC GMT900's didn't use them, I'm not sure why. I've heard guys say the RC's couldn't use them. but I'm not totally sure why.

    I've wondered if with the less mounting points, these mounts would provide too much play between the cab and front body panels, where with a 6 point mount, the front 4 mounts would provide the stability, and the rear could be used to dampen the ride, but with a 4 mount setup, the front mount would act more like a fulcrum for movement and may cause problems with the mounting points for body panels on the firewall/frame...however that is nothing but speculation....if you end up trying it out, let us know how it works.
     
  8. '89/'92Chevy/GMC

    '89/'92Chevy/GMC OBS Enthusiast

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    Been doing some reading and talking to a few engineers I know at school. It seems to me that the mounts will fit dimensionally, but like Aloicious just said, the fact that there are less mounts on the reg cab allows for more flex. With this higher amount of flex there are potential problems keeping front end sheet metal aligned. A certain degree of rigidity is required to keep everything lined up when road forces are added, such as bumps, speed, wind, etc. and the new rear mounts are not rigid enough for that purpose. That is why even on the GMT900 reg cabs they still use the same 4 mounts as the GMT400. Something also to think about is with enough force on the less rigid mount you will get more movement, with the greater amount of movement the more fatigue you will get on mount bolts.

    I don't think I am going to risk trying this mod on a reg cab, but if I ever get an EC I will most definitely try this.
     
  9. tylers88

    tylers88 I'm Awesome

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    I might have to try this on my 04 crew cab
     
  10. Aloicious

    Aloicious Hired Goon

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    it should work without a problem on a GMT800 crew cab.
     

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