Shackle placement and length

[Canadianmoose bogger]

Hi guys am new to this web sight and joined it because of the thread I seen on home made lift. I currently am building a sub frame lowering leaf spring mounts on my 79 blazer. I an also relocating the front shackle to the front of my blazer. My big question is how do you calculate where the front mount should be as i have seen they are never strait at each other and how long should my shackles be. I will also be running longer leaf springs and possible moving my front axle forward.This is my first big strictly off road truck. All others have been street legal and i installed manufactured lifts running 33- 37s I was wondering what gears you would run. It will be a trail rig and mud racer. I am running stock 350 welded Dana 60 and welded 14 bolt I am running 42 inch fire stone vtreads that are 11 inches wide. There max spread is 55 mph. So any advice any one can give me would help. Thanks guys
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[MTCK]

Welcome to the site! The 52" spring swap is common on the front and diy4x.com has a good kit. Also off road design makes a zero rate add-a-leaf that allows you to move the axle forward or back a bit. Why are you moving the shackle to the front? Most of the swaps I have seen move from the front to the rear.

Gears are more dependant on your motor. I have a buddy who has a mud drag truck. He runs 4.56 gears with 39.5 boggers, but his motor is a 406 small block ~600 horse and he goes through the lights at about 7000 rpm, so obviously a little different. He runs low range in his t-case and I think gets into 3rd gear on his TH350.

Anyways, post up some pics and guys will surely help you out on here.

[Canadianmoose bogger]

Ok thank for the advice. I am moving the shackle to the front of my leaf on my front leaf to angle my dif and I will be posting pics when I have time. I was wonder if there was a formula to the bracket placement and shackle length because i will be lowering my mount and moving them. I have seen those kits on the net but I will lower leaf spring mounts and it will be Easyer and stronger for me to build them for my self
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[ghettoluxury]

I would leave the swing shackle at the rear of the spring. GM put them there for a reason, a front axle should rock back when hitting something then pop forward. If you you move the swing shackle to the front then the suspension will be working against it's self. If you are running 42" tires you will want nothing higher than 5.13 gears.

[rcbildr]

If you do a Google search on leaf spring suspension design, or building a leaf spring suspension you will find a lot of helpful information on shackled location. It's what I do when I have questions on my 4x4 conversion.
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[Canadianmoose bogger]

Ok thank you that's the best info so far
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[fun in dirt]

Originally Posted by Canadianmoose bogger

My big question is how do you calculate where the front mount should be as i have seen they are never strait at each other and how long should my shackles be. I will also be running longer leaf springs and possible moving my front axle forward

The way we do it is to go ahead & put the springs you're wanting to run on the axel. Then roll it all up under the truck to find where the front mount needs to be to keep the axel centered in the wheelwell. Find the amount of rear shackle length you need by using some 2x4s or such to slowly & easily lower the truck's full weight down onto the springs then measure length from springs eyes to the frame mounting point. This may take several times of adding blocks & measuring to get it like you want. A friend with a big tractor to lift the front of the truck up & down is very handy & much safer than fooling with jacks. Just be careful & use jack stands!!!

[rcbildr]

Originally Posted by fun in dirt

The way we do it is to go ahead & put the springs you're wanting to run on the axel. Then roll it all up under the truck to find where the front mount needs to be to keep the axel centered in the wheelwell. Find the amount of rear shackle length you need by using some 2x4s or such to slowly & easily lower the truck's full weight down onto the springs then measure length from springs eyes to the frame mounting point. This may take several times of adding blocks & measuring to get it like you want. A friend with a big tractor to lift the front of the truck up & down is very handy & much safer than fooling with jacks. Just be careful & use jack stands!!!

That's an awesome idea. I'm going to have to try that on my project.

[68 TT]

Originally Posted by fun in dirt

The way we do it is to go ahead & put the springs you're wanting to run on the axel. Then roll it all up under the truck to find where the front mount needs to be to keep the axel centered in the wheelwell. Find the amount of rear shackle length you need by using some 2x4s or such to slowly & easily lower the truck's full weight down onto the springs then measure length from springs eyes to the frame mounting point. This may take several times of adding blocks & measuring to get it like you want. A friend with a big tractor to lift the front of the truck up & down is very handy & much safer than fooling with jacks. Just be careful & use jack stands!!!

Nice trick with the 2x4 zip tied to the spring eye.