1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

K10/K20 frame

Discussion in 'Suspension, Steering & Brakes' started by Jalopy_J, Sep 11, 2019.

  1. Jalopy_J

    Jalopy_J Junior Member

    Posts:
    10
    Likes Received:
    8
    Joined:
    Jul 15, 2018
    Location:
    Wichita
    First Name:
    Jesse
    Truck Year:
    1976
    Truck Model:
    K10
    Engine Size:
    350
    I was at a salvage yard last weekend and almost nabbed the rear springs off a 76 K20. My truck has the HD front spring (3 leaf) option, but not the HD rear leaf option, and the front sits noticeably taller than the rear (that HD front spring also rides like garbage). My dad said he remembers the truck being nose high like that since the day it was new. I figured the 8 leaf spring on the K20 might raise the rear a little over the 6 leaf on mine, but I'm guessing that 8 leaf is 56in instead of a 52in. I've read on at least a dozen threads on this forum that K10 and K20 frames are identical, and that the frame already has holes drilled to move the rear spring mount back 4 inches for a 56in spring. My truck sure doesn't have those second set of holes in the frame. I would have to drill 8 holes in the frame if I want a 56in spring. I'm curious to hear what others' thoughts are, but it seems there's some incorrect information floating around about the frames.
     
  2. 75gmck25

    75gmck25 Full Access Member

    Posts:
    633
    Likes Received:
    287
    Joined:
    Oct 13, 2016
    Location:
    VA
    First Name:
    Bruce
    Truck Year:
    1975
    Truck Model:
    K25
    Engine Size:
    5.7
    My '75 GMC is an 8200 GVW camper special, and it still uses 52" springs. I believe they are 7 leaf, and this is the highest GVW available in '75 for a 3/4 ton.

    Be prepared for a fairly rough ride, especially if you use the 10 ply rated tires that go along with those springs. It begins to ride better once you get about 1000 lbs in the bed. However, it also handles weight extremely well. I accidently overloaded it when getting rid of some old brick, and it handled a lot more weight than the GVW listed.

    Bruce
     
    donnieray likes this.
  3. bucket

    bucket Super Moderator Staff Member

    Age:
    37
    Posts:
    19,347
    Likes Received:
    4,176
    Joined:
    Aug 3, 2010
    Location:
    Usually not in Ohio
    First Name:
    Andy
    Truck Year:
    '77, '78, '79, '84, '88
    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    Even with higher capacity, longer springs can improve the ride quality. My '88 Burb came with 5 or 6 leaf 52's (can't remember which) and I installed a set of 8-leaf 56's from an '83 C30 and the ride was actually better than stock. And no more saggy butt when towing.
     
    78C10BigTen likes this.
  4. QBuff02

    QBuff02 I like Big Blocks and I cannot lie

    Posts:
    354
    Likes Received:
    433
    Joined:
    Feb 28, 2017
    Location:
    Central IL
    First Name:
    Quincy
    Truck Year:
    1982
    Truck Model:
    K30
    Engine Size:
    454
    1/2 and 3/4 ton trucks use a 52" rear spring and 1 ton trucks use 56" rear springs. If I remember there were a select few of the heavy duty sub-one tons that used a 56" rear spring but very limited. So you should have no problem swapping out the springs direct.
     
  5. bucket

    bucket Super Moderator Staff Member

    Age:
    37
    Posts:
    19,347
    Likes Received:
    4,176
    Joined:
    Aug 3, 2010
    Location:
    Usually not in Ohio
    First Name:
    Andy
    Truck Year:
    '77, '78, '79, '84, '88
    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    Many 3/4 tons used 56" springs.
     
    Arkansas_V8 likes this.
  6. QBuff02

    QBuff02 I like Big Blocks and I cannot lie

    Posts:
    354
    Likes Received:
    433
    Joined:
    Feb 28, 2017
    Location:
    Central IL
    First Name:
    Quincy
    Truck Year:
    1982
    Truck Model:
    K30
    Engine Size:
    454
    I've only seen one 3/4 ton with 56" rear springs. Is it a year split thing? Because I would say 85% of my square work/experience is north of the 80 model year. I have seen some frames with the extra holes already in them though but a lot of frames don't and I hear people say that they all should.. I do know they tell you to measure spring lengths when ordering lift kits, but apparently they're a little more spread than I figured them to be @bucket
     
  7. Craig 85

    Craig 85 Full Access Member

    Posts:
    1,877
    Likes Received:
    1,172
    Joined:
    Jan 25, 2017
    Location:
    Grass Valley, CA
    First Name:
    Craig
    Truck Year:
    1985
    Truck Model:
    K30 SRW
    Engine Size:
    454/TH-400/NP205
    I've had (2) 3/4 ton trucks and Suburban with 454's. All had the 56" springs.
     
  8. bucket

    bucket Super Moderator Staff Member

    Age:
    37
    Posts:
    19,347
    Likes Received:
    4,176
    Joined:
    Aug 3, 2010
    Location:
    Usually not in Ohio
    First Name:
    Andy
    Truck Year:
    '77, '78, '79, '84, '88
    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    I've seen a lot with 56's. Worked in a garage, worked a junkyard and spent a lot of time in other junkyards. I've owned 4 different 3/4 ton Burbs with 56's. Two of those were 2wd big blocks, the other two were 4x4 small blocks. A '78, a couple 86's and a '90. They were very common in 3/4 tons, and even used in 1/2 tons too.
     
  9. Jalopy_J

    Jalopy_J Junior Member

    Posts:
    10
    Likes Received:
    8
    Joined:
    Jul 15, 2018
    Location:
    Wichita
    First Name:
    Jesse
    Truck Year:
    1976
    Truck Model:
    K10
    Engine Size:
    350
    The main question though was does anyone here have holes in the frame to mount the bracket for BOTH 52 and 56 springs? I've seen a dozen threads here that say K10 and K20 frames are the exactly same. I think this is probably wrong, at least it was in 76. No K10 had 56in springs, and my K10 frame does not have provisions for that. Maybe that's the only difference in a K10 and K20 frame, maybe there are other changes as well (strength, geomemtry, etc, idk), but I was surprised to see the lack of holes given the amount of threads I've read stating that otherwise.
     
  10. yevgenievich

    yevgenievich Full Access Member

    Posts:
    3,535
    Likes Received:
    1,042
    Joined:
    Mar 1, 2014
    Location:
    Texas
    First Name:
    Viktor
    Truck Year:
    1991
    Truck Model:
    V2500 burb
    Engine Size:
    5.7
    The manuals stated thickness difference on k10 vs k20. If there is no holes, likely there is some indication on the frame where the mounts would go. My 3/4 burb has the 56" springs.
     
  11. bucket

    bucket Super Moderator Staff Member

    Age:
    37
    Posts:
    19,347
    Likes Received:
    4,176
    Joined:
    Aug 3, 2010
    Location:
    Usually not in Ohio
    First Name:
    Andy
    Truck Year:
    '77, '78, '79, '84, '88
    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    Yes, all three of my K-Burbs have had the holes in the frame for both spring lengths. I'm pretty sure many trucks did too, but I don't currently have one so I won't guarantee it.
     
  12. Jalopy_J

    Jalopy_J Junior Member

    Posts:
    10
    Likes Received:
    8
    Joined:
    Jul 15, 2018
    Location:
    Wichita
    First Name:
    Jesse
    Truck Year:
    1976
    Truck Model:
    K10
    Engine Size:
    350
    So it sounds like K10 and K20 frames are actually a lot different then. (And what "manuals" stated this, btw? I'd be interested to read it.) A lot of bad info floating around then it seems. An no, there is no "indication on the frame" of where the mount would go. I'd just have to measure 4" back from the current holes.
     
  13. Jalopy_J

    Jalopy_J Junior Member

    Posts:
    10
    Likes Received:
    8
    Joined:
    Jul 15, 2018
    Location:
    Wichita
    First Name:
    Jesse
    Truck Year:
    1976
    Truck Model:
    K10
    Engine Size:
    350
    K20's would have because those came with 52 or 56 depending on options. I was just surprised reading here that K10s had both as well because they were the same frame, when (at least in 76) they weren't.
     
  14. 86 SCOTTSDALE

    86 SCOTTSDALE Supporting Member Supporting Member

    Posts:
    73
    Likes Received:
    40
    Joined:
    Apr 10, 2019
    Location:
    Oakham MA
    First Name:
    Armand
    Truck Year:
    1986
    Truck Model:
    K10
    Engine Size:
    305
    My 86 K10 has holes for both.
     
  15. Rusty Nail

    Rusty Nail Whatever! Supporting Member

    Posts:
    4,428
    Likes Received:
    2,248
    Joined:
    Jan 29, 2015
    Location:
    MAGA Country
    First Name:
    Rusty
    Truck Year:
    1977,1988
    Truck Model:
    C20, K5
    Engine Size:
    350, 350
    I don't buy a 10 frame is the same as a 20.
    That sounds ridiculous.
     

Share This Page