X code springs under a Cummins
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New User
Joined: Mar 2019
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From: Surprise, AZ
X code springs under a Cummins
So, some background info. I’m putting together a 6b powered 78 F250. I’ve scoured the depths of the internet(including FTE), but couldn’t necessarily find the answer I was looking for. I’m looking to gain a little height, but not enough to justify a 4 inch lift. I’ve read countless threads about how stock SD springs net roughly 2” of lift, but all of those were on gassers. So my question is, will X codes still net that much lift under the weight of a Cummins, or would I be wasting time with that swap?
Cargo Master
Joined: Nov 2007
Posts: 2,238
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According to this sites info, if it's correct, the X code is 1/16" thinner but has 2 7/8" more arch than a 77-79, so 2 13/16" more lift with everything being the same.
77-79
https://www.sdtrucksprings.com/index...oducts_id=7757
X code
https://www.sdtrucksprings.com/99-04...-leaves-x-code
I have the parts to do this to my 78 once I get the time, used stock X codes and 12V drive train. I've done a ton of research. With the cummins, I'm hoping for 2" based off the spring differences and added weight. Plus I'll be running a plow frame and HD bumper.
Another thing to know. The X codes front half is longer, so it pushes the axle back about 1 1/2". A offset zero rate leaf can recenter it and add another inch if the springs aren't enough. You can also use shackle length to dial in the final height, to a point. The problem I don't like is the zero rates keeps the front spring length the same as a stock 78 spring. IDK if this is slightly negating the effects of adding the longer spring if all the length ends up on one side. I'm hoping to move the front spring mounts to keep the axle /spring together on the original center pin, and keep the axle centered like stock. I think it'll end up with the best performance overall. I'm also planning on changing my shock mounts so I can run off the shelf +2-4" super duty shocks. I think the minor amount of fab work, well for me, will be well worth it.
77-79
https://www.sdtrucksprings.com/index...oducts_id=7757
X code
https://www.sdtrucksprings.com/99-04...-leaves-x-code
I have the parts to do this to my 78 once I get the time, used stock X codes and 12V drive train. I've done a ton of research. With the cummins, I'm hoping for 2" based off the spring differences and added weight. Plus I'll be running a plow frame and HD bumper.
Another thing to know. The X codes front half is longer, so it pushes the axle back about 1 1/2". A offset zero rate leaf can recenter it and add another inch if the springs aren't enough. You can also use shackle length to dial in the final height, to a point. The problem I don't like is the zero rates keeps the front spring length the same as a stock 78 spring. IDK if this is slightly negating the effects of adding the longer spring if all the length ends up on one side. I'm hoping to move the front spring mounts to keep the axle /spring together on the original center pin, and keep the axle centered like stock. I think it'll end up with the best performance overall. I'm also planning on changing my shock mounts so I can run off the shelf +2-4" super duty shocks. I think the minor amount of fab work, well for me, will be well worth it.
Thread Starter
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New User
Joined: Mar 2019
Posts: 9
Likes: 0
From: Surprise, AZ
That’s what I was hoping to hear. I didn’t know if the lift was achieved by the fact the springs had a higher rate mixed with a longer shackle or if they truly had more arch. I’ve read a couple examples of guys who swapped springs and ended up lower than they did to begin with. I did plan on running zero rates to compensate for the axle push. I guess it’s all systems go then.
Cargo Master
Joined: Nov 2007
Posts: 2,238
Likes: 475
That’s what I was hoping to hear. I didn’t know if the lift was achieved by the fact the springs had a higher rate mixed with a longer shackle or if they truly had more arch. I’ve read a couple examples of guys who swapped springs and ended up lower than they did to begin with. I did plan on running zero rates to compensate for the axle push. I guess it’s all systems go then.
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