spring shims

73lndcrsr

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I am sure this has been discussed, but I can't seem to find a good answer.

I am installing a 4" lift with longer shackles. What is the best way to determine the amount of shim to be used? I have heard about 1* for each inch of lift. &nbsp:Does this sound right?

Thanks in advance for the help.
 
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Why guess when you have trigonometry? The spring is about 42 inches long, so for an increase in shackle length of 1 inch:
sine of 1/42 = .0238; the angle whose sine is .0238 (arcsin or inv sin on your calculator) is 1.36 degree. :D
 
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thats only if the shackle is at a right angle to the frame.i think ;)
 
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Dec 13, 2002
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well pinhead, you aint so much a pinhead huh?
all i can say is WHAT? :D
you do speak english correct?
cause that aint english :D
 
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That is trigonenglish. You can find the angle for any right triangle where you know the rise and run length. Just divide the rise by the run length on you scientific calculator (windows comes with one) and then hit the "INV" and then "SIN" buttons to determine the angle. It works every time and it is rocket science.
 
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I have 4"lift with long shackles I use 2.5*shims up front and 4*in back works great good steering and pinion angles
 
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My 4" TPI lift came with 6 degree shims up front. Dont forget the fat end goes forward or you'll be driving your Cruiser with one finger like I was for a day or two :eek:
 
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My 4" TPI lift came with 6 degree shims up front. Dont forget the fat end goes forward or you'll be driving your Cruiser with one finger like I was for a day or two :eek:
I'm not picturing this right. I was thinking it would need to go towarss the back? Wouldn't the fat end in the front point the pinion down?
 
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Wouldn't the fat end in the front point the pinion down?


Yes, fat end in front points the pinion down to where it was before you added the longer shackles. More importantly it also rotates the top of the knuckles back to give +1 degree caster.

You only point the pinion at the transfer case if:
1) you cut and turn the knuckles to achieve the proper caster angle.
2) you run a CV joint at the Tcase.
 
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Yes, fat end in front points the pinion down to where it was before you added the longer shackles.  More importantly it also rotates the top of the knuckles back to give +1 degree caster.

You only point the pinion at the transfer case if:
1) you cut and turn the knuckles to achieve the proper caster angle.
2) you run a CV joint at the Tcase.  
Thanks for the clarification.
 
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ok...

i'm fine with trig but i am having trouble visualising the triangles...

my problem is that my front main leaf in the springs have had about 1.5 inches added to the front of them...

so how do i work out how much castor correction i need
 

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