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Frame differences 3/4 vs 1 ton

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by dremu, Oct 12, 2004.

  1. dremu

    dremu Officious Thread Derailer Premium Member

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    Yeah ... I know it's sorta been covered before, but I have a twist. See, I heard this rumour that sixpacks /forums/images/graemlins/crewcab.gif (at least in the early 70's, like my '74) all had a 1-ton frame, even if they were 3/4 ton. Being the curious type, I wanna know if this is true.

    So I found this page which lists a boatload of different frames and dimensions, but it's so complicated it makes my head spin. I *think* I have an answer and my truck is the CA314... but I'd love to hear any ideas there.

    However, I did take a couple of comparative measurements between the pickup in question and my Blazer (also a '74).

    I note the Blazer frame is ~1/8" thick, at least on the bottom edge I could get at conveniently, and the pickup is much thicker -- like 3/16".

    I also note that my 14-bolt has springs which are 39 1/2" center to center, but that just prolly means they're your usual 3/4 ton springs. The Blazer's gas tank and skid plate are in the way, or I'd compare it to the Blazer.

    From the frame thickness, I'm inclined to believe that it IS indeed a 1-ton frame ... can anyone prove or disprove this?

    And finally, am I supposed to measure springs and perches center-to-center, or outside, or ... ?

    -- A
     
  2. virgilh

    virgilh 1/2 ton status

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    if you measure the height of the frame i'll compare it to my k30 thats the difference of 1/2 3/4 ton frames to 1 ton frames also the thickness of the frame but im not getting under the truck with a set of calipers /forums/images/graemlins/thumb.gif
     
  3. BigBlockBurris

    BigBlockBurris 1/2 ton status

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    Every crew cab I have ever seen has had a 1 ton frame. I parted a 74 and it was a 3/4 ton but it had a ton frame. I read somewhere (I can't remember where) that all crew cabs were ton frames regardless of suspension rating. Hope this helps.

    BBB /forums/images/graemlins/crewcab.gif
     
  4. hawkeye649

    hawkeye649 1/2 ton status

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    [hijack]
    Has anyone ever bobbed a K30 frame in the right places to make it fit under a K5?
     
  5. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    The shape is all wrong to easily fit and would require extensive modifications to the K5 tub.
     
  6. hawkeye649

    hawkeye649 1/2 ton status

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    Thought it might be a little better as too torsional loads....
    I always thought a K5 was based on a shortened K10 frame, and that was why there was a 6" rise just behind the front seats? /forums/images/graemlins/confused.gif
     
  7. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Early second gens would be easier, later tubs have a rear foot well that would need channeling. IIRC, the pickup version rises higher and further forward (actually under the seats, not behind), and the body mounts past the fire wall are different.
     
  8. hawkeye649

    hawkeye649 1/2 ton status

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    Doesn't that mean tha a crew cab would raise far enough back to make it work?

    I'm not talking about just cutting off the end & calling it done. I had assumed some would have to come out of the middle, maybe even shorter cross members /forums/images/graemlins/ears.gif
     
  9. R72K5

    R72K5 Banned

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    crewcabs were all 1 ton chassis yeah

    1 ton has taller frame rails than 3/4 and 1/2 tons do

    in 68-72 there was a model called the longhorn pickup, they were only built 20 and 30 series, both used the 1 ton chassies, so there was a 3/4 ton being built at factory using a 1 ton chassis but was badged as a 20 on purpose, even the spring packs were 40 apart

    youre measrugin 39.5 but its stillt echnicallyh 40 no matter what you call it or think it is, gm only had 40 and 42.5 pack spacings been this way since at least 63 or 63 on all the trucks 30 series and under



    same with the crew cabs 73-up you could get a 3/4 ton crew cab but it was a 1 ton 40 apart spring pack chassis of course(none factory built until after 72 some time)

    also the R03 dual real wheel conversion package was available for 20 series trucks ofr at least 67-72 years, dunno about before or after

    i can list technical details straight from gm model year options sheets for most of these
     
  10. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    [ QUOTE ]
    Doesn't that mean tha a crew cab would raise far enough back to make it work?

    I'm not talking about just cutting off the end & calling it done. I had assumed some would have to come out of the middle, maybe even shorter cross members /forums/images/graemlins/ears.gif

    [/ QUOTE ]
    Sorry, don't know the answer to that one. Do some measuring and let us know. /forums/images/graemlins/laugh.gif
     
  11. rubbinz raczn

    rubbinz raczn 1/2 ton status

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    don't mean to hijack but since 1st gen. frames have come in to the conversation here goes. randy of all the people that know 1st gen stuff you seem to be the one that knows most. /forums/images/graemlins/bow.gif my 4x4 is a 1967 gmc camper cruiser. it was a 3/4 ton 2wd had the rear d60 axle when i pulled the body off frame i was impressed at how the frame had factory gussets at every crossmember. spring spacing was 42.5 and leaves in rear were 9 ever heard of one of those? thanks lonnie /forums/images/graemlins/dunno.gif
     
  12. dremu

    dremu Officious Thread Derailer Premium Member

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    [ QUOTE ]
    youre measrugin 39.5 but its stillt echnicallyh 40 no matter what you call it or think it is, gm only had 40 and 42.5 pack spacings been this way since at least 63 or 63 on all the trucks 30 series and under


    [/ QUOTE ]

    Oh, no argument from me -- that's sitting in the fricken street, so I wasn't gonna quibble over fractions of an inch! /forums/images/graemlins/laugh.gif

    Hmmm... soooo if I got bored someday, I could drop in a set of springs off a 1-ton in the rear ... any idea of what's different in the C30's (i.e. 1-ton 2WD's) up front ... ya think the rotors and stuff are the same? coil springs prolly are bigger on the 30's... anything else?

    -- A
     
  13. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    2WD front suspension is identical on 3/4 and 1 ton trucks. Only significant diff is that the 1 tons have a dually spacer. Springs, A-arms, spindle, even the cradle are all the same.
     
  14. dremu

    dremu Officious Thread Derailer Premium Member

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    [ QUOTE ]
    if you measure the height of the frame i'll compare it to my k30 thats the difference of 1/2 3/4 ton frames to 1 ton frames also the thickness of the frame but im not getting under the truck with a set of calipers /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    Okay. Finally I had a combination of ffee time and no rain /forums/images/graemlins/waytogo.gif

    I measured the frames just in front of the rear axle in the wheelwell, as it was a convenient place to get to the frame ... and the ends taper by the bumpers, I suspect.

    The /forums/images/graemlins/k5.gif frame is ~6" tall, and the /forums/images/graemlins/crewcab.gif is ~7.5", so I'm gonna betcha your K30 is the same.

    Randy-san, do those measurements sound about right for the taller frame on a 1-ton?

    -- A
     
  15. dremu

    dremu Officious Thread Derailer Premium Member

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    [ QUOTE ]
    2WD front suspension is identical on 3/4 and 1 ton trucks. Only significant diff is that the 1 tons have a dually spacer. Springs, A-arms, spindle, even the cradle are all the same.

    [/ QUOTE ]

    Cool! Now, I don't think that *all* one ton's were duallies (nor were all 3/4's SRW ... pretty sure both GVWR's came in both wheel types) ... but that's good info. LMC doesn't touch the 30-series, and my real Chevy books are still boxed from the move /forums/images/graemlins/laugh.gif

    Thanks! /forums/images/graemlins/waytogo.gif

    -- A
     
  16. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    I thought all C30s were duallys, and the only C20 duallys I've heard of are the pre-72 trucks. But I could certainly be wrong on that.

    I'm sure about the rest though since I once made quite a bit of coin converting old drum front trucks to disks, including several C20/30 trucks. My old 69 GMC 11k car hauler got a complete front cradle from a 78 3/4 ton Chevy to upgrade suspension and disk brakes to more common, cheaper and easier to find later model components.
     
  17. dremu

    dremu Officious Thread Derailer Premium Member

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    [ QUOTE ]
    I thought all C30s were duallys, and the only C20 duallys I've heard of are the pre-72 trucks. But I could certainly be wrong on that.


    [/ QUOTE ]

    Well, rooting through the brochures, I see lots of "Dual rear wheels are available" ... but only for 30-series, so by the looks, we're both half right. No 3/4-ton duallies (at least, say, 73-80ish) and 1-ton's were available in both.

    [ QUOTE ]

    I'm sure about the rest though since I once made quite a bit of coin converting old drum front trucks to disks, including several C20/30 trucks. My old 69 GMC 11k car hauler got a complete front cradle from a 78 3/4 ton Chevy to upgrade suspension and disk brakes to more common, cheaper and easier to find later model components.

    [/ QUOTE ]

    Sweet! That makes my life easier, as it just means I could conjure a set of the 1-ton springs, and beef up the old girl nicely.

    -- A
     
  18. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    I have a set of the one ton springs if you feel like paying shipping, they are free
     

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