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Using K30/3500 (GM 1-ton) Leaf Packs


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My main leaf springs have seen better days. So I started down the "what JY swap will work?" path before dropping $500+ and came across old GM 1-ton springs. They are only 1" shorter in the rear than the Comanche's (30" vs 31"). They also use 9/16" bolts. Ours are M14, but it's literally .01" difference so should snug in there just fine.

 

So I got to wondering if you could swap them & if anyone has tried. I've already got drop shackles which have two different holes to adjust if needed. You can find these packs easily at a JY for $50 or even buy the main leaf for $75 new. Obviously I'm not sticking 9 springs under my truck, but thinking I could make a bastard pack if needed. I'm not sure the arch though.

 

Anyone have any insight?

 

IMG_2057(2).JPEG.d9c72bb1d4b02b0afb50ffca5dd42be1.JPEG

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my biggest concern is that the shackle angle will be wrong and it might invert when the truck comes down off a lift or flexing offroad.  :( 

 

if you keep your main leaf, you can swap all sorts of packs under them. :L:  

 

what is it that you want the new packs to do?  lift?  greater capacity?

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Dirt road is about the only off-road it'll see in this condition, and no one is lifting it but me so those are a plus I suppose. You're thinking I should keep my main even though they're bent the wrong way? Curious what's the reasoning?

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On 12/31/2021 at 10:57 PM, PocketsEmptied said:

Dirt road is about the only off-road it'll see in this condition, and no one is lifting it but me so those are a plus I suppose. You're thinking I should keep my main even though they're bent the wrong way? Curious what's the reasoning?

 

How are they bent the wrong way? I dodn't see that in your photo.

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I guess I mean they're just so worn that once under an actual load and start to flatten, the main starts to invert. Don't have a pic showing since I don't have a load in the bed. But if there's no integrity issue with the main doing this then I could do as Pete suggested and add another leaf under it.

 

Ultimately was trying to find a JY main leaf replacement. Thought this was a decent idea.

 

@Pete MDo you remember what that leaf came off of? Looks like it should be about 50-52" or so at the length you have in your photo. I'm sure I would need to cut something

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I looked at these before I think...  And they are flatter than factory MJ springs.  You would also have to do something about the shackle location.

 

I wanted them to go SOA and not get 5-6" of lift.

 

I didn't buy them because it cost too much to gamble at the time, and the springs I had proved to perform fine in the end, even if a little too tall.

 

 

Edit, I think I was looking at "C" truck (2wd) springs actually.   I need to go dig into that again.

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It sure doesn't look like the GM springs have anywhere near enough arch according to the charts. Most people don't realize that the Mj might have one of the steepest if not steepest factory arch over any other produced. Like way more at around 9.5" it smokes doubles even triples most factory rear leaf arches. I have used Durango main leaf from early 2000s if I recall correctly with some luck. It was about the close as dimension arch and eye I could find on any chart however there was still a pretty big discrepancy in arch. My leaves were soo worn though I got lucky and found a set of Durango that the sags matched near perfect but brought the arch up overall. The main from the Durango had a higher psi strength and payload, again if I recall correctly near a metric mj if you found the right Durango setup. It's dangerous to have less a tensil strength main than the others in the pack. The main will sheer first. Also you need the same arch for the leaves otherwise they fight one another when flexed also potentially causing shearing. Making something work temporary vs right are two different things. I just know the amount of time I spent building my own was only worth it cause I had to for my daily work truck at the time. New u-bolts, centering pins, clamps, and isolators add up even going cheap not replacing bushings. Time wasn't on my side. In all it worked decent but I would never go that route again. You'll spend a day at least trying to pull, build, and swap in packs. Time is money. I'd work the extra day or two and just order a brand new set if your having to buy or source your donar parts if you don't already have them.

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On 1/5/2022 at 2:54 AM, saveevryjp1998 said:

It sure doesn't look like the GM springs have anywhere near enough arch according to the charts.

 

Which charts are you using?  I'm looking for springs that are flatter than the stock MJ springs, so I can go SOA with a little higher spring rate and not get more than 4"~ lift.  If that's possible without a custom spring.

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4 hours ago, zomeizter said:

I scored a set of rear leaves off a 99 Silverado HD which will be swapped in once I get some home time. I mocked them up under the 'manche and they look like they could work, maybe some shackle bracket relo will get them mounted...

 

Technically a lot of springs will work with shackle mount relocation lol, but I was trying without doing so. I don't have a welder or I would try. 

 

1 hour ago, DirtyComanche said:

 

Which charts are you using?  I'm looking for springs that are flatter than the stock MJ springs, so I can go SOA with a little higher spring rate and not get more than 4"~ lift.  If that's possible without a custom spring.

 

Technically the Comanche is 11.75" from bottom to top of eye. The GM springs are 9.125" from bottom to top of eye. However, if you were to keep all 8 leafs, I have no idea how much the rear end would sit down since it would have a lot more reinforcement. But you could certainly remove them.

 

image.png.d92d255902d275f851d0c696dcec1051.png image.png.5a17556793f4fe9386fd6f5bc9048c52.png

 

Early Ford Ranger springs are only 3/8" shorter than the Comanche's and the total height is much lower. Maybe you could get away with those and an AAL? Dunno

 

image.png.d3e92b09f40550d9b82b0ce49589e4ed.png

 

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12 hours ago, PocketsEmptied said:

 

Technically a lot of springs will work with shackle mount relocation lol, but I was trying without doing so. I don't have a welder or I would try. 

My bad, I thought you were after swapping in GM 1 ton springs...

 

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On 1/8/2022 at 6:24 PM, PocketsEmptied said:

 

Technically a lot of springs will work with shackle mount relocation lol, but I was trying without doing so. I don't have a welder or I would try. 

 

 

Technically the Comanche is 11.75" from bottom to top of eye. The GM springs are 9.125" from bottom to top of eye. However, if you were to keep all 8 leafs, I have no idea how much the rear end would sit down since it would have a lot more reinforcement. But you could certainly remove them.

 

image.png.d92d255902d275f851d0c696dcec1051.png image.png.5a17556793f4fe9386fd6f5bc9048c52.png

 

Early Ford Ranger springs are only 3/8" shorter than the Comanche's and the total height is much lower. Maybe you could get away with those and an AAL? Dunno

 

image.png.d3e92b09f40550d9b82b0ce49589e4ed.png

 

 

A Ranger lift spring look like a possible good option, if one could find them, or add another cut down main leaf.  Or like you say, take the GM spring and maybe pull 3 leaves out of it.  Definitely some options.

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