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Front & Rear Leaf Springs for C and K Models

Discussion in 'Lowered & Street Systems' started by HotRodPC, Oct 6, 2010.

  1. HotRodPC

    HotRodPC Administrator Staff Member

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    Ever wondered what size leaf springs you have on your Squarebody truck? Here is some info I put together for another forum that obviously didn't appreciate it much. I have a K10 that I am converting to a K20. This research answered alot of my questions for me. Notice a C10 and a K20 are the only models that could possibly have either the 52 or the 56 inch springs depending on the RPO code and factory installed equipment. BTW, both frames C and K are punched to be able to accept both size springs. The spring hangers are the same for 52 or 56 inch springs. So if you want to change your spring size, simply grind off the rivets, and use grade 8 bolts to relocate your spring hangers in the other set of holes already punched in your frame from the factory. One of the many things I love about GM, making things very universal and interchangeable. But, do keep in mind, C and K frames do use differant spring hangers. So although you can move the hangers to change your spring size, you must use K hangers for the K frame, and C hangers for the C frame. Very simple if whatever truck you are working on, simply use the same hangers on the truck you are working on, and they can be relocated without any fabbing or welding whatsoever.

    Front Leaf Springs
    K10, K20, and K30 Use the same springs. Differance is, they come in 2 leaf, 3 leaf or 4 leaf set up. All 3 set ups are interchangeable between all 3 models.
    I'd imagine the K30 comes in the 4 leaf set up, but the K10 and K20 could be either the 2 or 3 set up depending on heavy duty RPO code or not.

    Rear Leaf Spring 2WD C10, C20, C30.
    C10 can be 52 inch or 56 inch springs. Depending on Heavy Duty RPO code.
    C20 is 56 inch springs. # of leafs and thickness of spring pack depends on RPO code, ie... Smooth Ride, Heavy Duty etc.
    C30 is 56 inch springs. # of leafs and thickness of spring pack depends on RPO code. 10 Leafs is Heavy Duty 1 ton.

    Rear Leaf Springs 4WD K10, K20, K30.
    K10 is 52 inch springs. # of leafs and thickness of pack depends on RPO code.
    K20 can be 52 inch or 56 inch springs. Depending on Heavy Duty RPO code or not. (Appears that 52 inch may be more common)
    K30 is 56 inch springs. # of leafs and thickness of spring pack depends on RPO code.

    So becasue I am converting my K10 to a K20, with drum to drum axle swaps, I am also moving the rear spring hangers on the K10 which currently has 52 inch 1/2 ton springs, and I will be installing heavier 56 inch springs off of a C20 donor truck. For my 85 K10, the master cylinder is also the same for either the K10 or K20.
     
    Last edited: Oct 6, 2010
  2. crazy4offroad

    crazy4offroad Service Bullshit Filter Soon

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    Great info! If you plan on lifting it at all you might want to consider the shackle flip for the rear springs. I did with 56" springs and even with a thick leaf pack it rides like a Cadillac.
     
  3. HotRodPC

    HotRodPC Administrator Staff Member

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    I'd much rather do that than use blocks. I'll probably do that, then have a place here in OKC called City Spring makes me some front springs to lift the front. I think it would be much less expensisve than buying a lift kit.
    The reason I figured this info was important, I seen on another site where a younger guy has replaced his broken rear springs with a used set from a junkyard. Funny thing was, his truck had 52 in springs, and the donor truck he got springs from obviously had 56 springs. Can you believe the guy actually got the 56 to go on his truck without moving the hangers. LMAO, the shackle was all the way extended to the back of the truck. Talk about funny looking, and you know that had to ride like he was on solid blocks because there was no way that shackle could move at all. When someone pointed out he had the wrong springs, he asked if he could have the springs cut down cuz the poor kid didn't have money to buy another set of springs. Noone thought to tell the guy just to grind the 6 rivets off each the hangers, and use grade 8 bolts and move the hangers back and the problem was solved. 12 bolts and a couple hours work would have been alot cheaper than buying another set of springs he didn't need. And his truck would have rode smoother than before with more payload without sagging. I save all the 1/2 ton 56 inch springs I come across in my trucks.
     
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  4. crazy4offroad

    crazy4offroad Service Bullshit Filter Soon

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    LOL With the ORD shackle flip I used you can leave the supplied hanger in the stock location, and the shackle actually looks good! Looking at the driver's side the angle looks like 4 or 5 o'clock, pointing back at the bottom. I think this is partly why mine rides so good in the back now.

    You know you can move your stock 52" rear springs to the front and gain 4" dont ya? You have to cut/re-weld the front bracket for the front springs though. This is another popular mod for a soft ride up front, gain 4" lift, and cheap too!
     
  5. HotRodPC

    HotRodPC Administrator Staff Member

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    NO, I was not aware of the 52 in springs up front. I don't quite follow what you mean cut and reweld the front bracket. But I will sure look into and figure it out. 4 inch suspension lift is what I want, and no body lift. I also have a set of 10 leaf 1 ton springs already that came with a 14FF that I got for FREE, so I intend to use the 56 inch 10 pack leafs in the rear, then the 52 in rears, I can use up front. With the shackle flip and 10 pack 1 ton rear springs, that I oughta give me all the lift I want. I am so itching to get this ride together. I am still in process of building the motor and trans though. Slow project being done in small steps as funds are available. I oughta start a thread on the build soon so I am not getting off topic in this forum, as now its in Street Suspension and we are talking about lifts. Maybe our good ole fearless Administator can move it over to Lifted Suspension for us.
     
  6. crazy4offroad

    crazy4offroad Service Bullshit Filter Soon

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    I think stock the front springs are 48" so the front "eyelet" bracket that bolts the front of the front springs to the frame has to be relocated forward 2". I cant remember if much has to be done with the rear of the front springs, maybe longer shackles to allow for the 2" you need to go back for that part. If you've looked at factory front Chevy springs you see they are reverse arched. With the positive arch of the rear springs up there you gain quite a bit just having the springs arched the "correct" way. As for the 10-pack rears, you might need to take a couple out or you might end up with more than 4" of lift in the rear. Before you do anything get the truck sitting on a level spot and measure from the body line down to either the top or the centerline of the front hub. Write it down. Do the same for the back measuring to the top or centerline of the opening in the wheel for the rear axleshaft. Write this down too. This is so you'll know how much you are gaining afterwards and what you might need to add/subtract to get it to ride level. Always get your u-bolts a couple or 3 inches longer than you need. You can cut the excess off once you're done. (keep in mind the inboard u-bolt on the passenger side front is not only longer, but also wider than all the others because of where it goes over the center section of the housing)
     
  7. 77k10silverado

    77k10silverado Junior Member

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    So my stock 77 K10 has 2 up front and 6 out back. Is this standard? I don't see any RPO codes for heavy duty on my truck. What's standard for a K20?
     
  8. HotRodPC

    HotRodPC Administrator Staff Member

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    That sounds about right. One of the heavy duty RPO codes, is C6P. But that's pretty much the whole truck, not just springs. Things like a bigger radiator for example.
     
  9. MadOgre

    MadOgre Full Access Member

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    Great info ! Those other forums are just guys swearing at each other all day long cause they think they got bigger you know what, than the rest of us. waste of time.

    I have only ever had 52s, so im wondering does the 56 ride better or worse ? And ya I love the chevy mix and swap !

    It is interesting the rear to front spring thing but I think it would be a lot easier and better to pop the rivets on those front spring hangers and re drill new holes further forward, rather then cutting and welding.

    Im going from 6 to 4 and I already have a 2 inch add a leaf and 4 inch blocks in the rear. so im just gonna get 2 4 inch springs for the front and 2 2 1/2 inch blocks for the rear. and im gonna keep my 6 inch shocks on there till they wear out.
     
  10. MadOgre

    MadOgre Full Access Member

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    Also I think the arch in the rear would put you at about 5 inches maybe 6 ? when swapped to the front.
     
  11. HotRodPC

    HotRodPC Administrator Staff Member

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    The 56's not only ride more comfy since the bounce isn't as erratic or stiff, but yet firm, they also can carry more weight. I'm a 56in guy all the way. I will be putting 56in out of my C20's on my K10 in the rear. Now I'm not changing that arch at all. I am keeping the OEM arch by simply moving my rear spring hangers back 4inches. Same hangers being moved back to the holes that are already punched in the frame at the factory. Simple as grinding rivets, then using hardened bolts with Lok-Tite, to bolt them back on, and then use the 56in 3/4 2wd springs. This will give me about a 1-2 in lift in the rear due to the thicker spring pack. Then with 2in lift blocks, that will match my 4in front spring lift, and the truck should sit level with only using 2in blocks in the rear. The smaller the blocks, the less chance of axle wrap, so I don't want to go with 3 or 4in lift blocks.
     
  12. MadOgre

    MadOgre Full Access Member

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    I have foumd its easier to remove those rivets by wacking the rivet head off with a large cold chisel and a small hand sledge. it usualy only takes one or two wacks. you could have those hangers off in less then 3 minutes.
     
  13. Affende

    Affende Full Access Member

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    FWIW, my 84 K3500 3+3 w/ 454 & SM465 has a 3 leaf front pack.
     

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